NOTIZIARIO Neutroni e Luce di Sincrotrone - Issue 7 n.2, 2002

Rivista del Consiglio Nazionale delle Ricerche

NOTIZIARIO Neutroni e Luce di Sincrotrone

ISSN 1592-7822

Vol. 7 n. 2

Giugno 2002 - Aut. Trib. Roma n. 124/96 del 22-03-96 - Sped. Abb. Post. 70% Filiale di Roma - C.N.R. p.le A. Moro 7, 00185 Roma

NOTIZIARIO Neutroni e Luce di Sincrotrone Rivista del Consiglio Nazionale delle Ricerche Cover photo: X-ray interference between the two arrays of myosin heads in each bipolar myosin filament superimposes a finely spaced fringe pattern onto the M3 X-ray reflection originating from the ~14.5 nm axial repeat of the myosin heads along the filament. The effect is used to determine with sub-nanometric precision the motions of myosin heads during the execution of the working stroke that drives force generation and sliding between actin and myosin filaments in muscle contraction.

SOMMARIO EDITORIALE

......................................................................................

2

C. Andreani

RASSEGNA SCIENTIFICA The ALOISA Beamline at ELETTRA

..............................

3

F. Bruno et al.

Simulation of the Upgrade of the BackScattering Spectrometer IN13 at ILL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 C. Mondelli et al.

X-ray Interference Measures the Structural Changes of the Myosin Motor in Muscle with Å Resolution . . . 19 M. Reconditi et al.

Il

NOTIZIARIO è pubblicato a Neutroni e Luce di Sincrotrone

The Contribution of Neutron Scattering to Cultural Heritage Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

cura del C.N.R. in collaborazione con il Dipartimento di Fisica dell’Università degli Studi di Roma “Tor Vergata”.

Vol. 7 n. 2 Giugno 2002 Autorizzazione del Tribunale di Roma n. 124/96 del 22-03-96 DIRETTORE RESPONSABILE:

C. Andreani

R. Rinaldi et al.

PROGETTO E.S.S.

............................................................................

38

..................................................................................

39

............................................................................................

40

CALENDARIO

COMITATO DI DIREZIONE:

M. Apice, P. Bosi

VARIE

COMITATO DI REDAZIONE:

L. Avaldi, F. Aliotta, F. Carsughi, G. Ruocco.

SCADENZE

......................................................................................

42

FACILITIES

......................................................................................

43

SEGRETERIA DI REDAZIONE:

D. Catena HANNO COLLABORATO A QUESTO NUMERO:

F. Carsughi GRAFICA E STAMPA:

om grafica via Fabrizio Luscino 73 00174Roma Finito di stampare nel mese di Giugno 2002 PER NUMERI ARRETRATI:

Paola Bosi, Tel: +39 6 49932057 Fax: +39 6 49932456 E-mail: p.bosi@dcas.cnr.it.

PER INFORMAZIONI EDITORIALI:

Desy Catena, Università degli Studi di Roma “Tor Vergata”, Presidenza Facoltà di Scienze M.F.N., via della Ricerca Scientifica, 1 00133 Roma Tel: +39 6 72594100 Fax: +39 6 2023507 E-mail: desy.catena@uniroma2.it

Vol. 7 n. 2 Giugno 2002

EDITORIALE

A

partire da questo numero il dott. Franco Aliotta entra a far parte del Comitato di Redazione in sostituzione del prof. Ulderico Wanderlingh.

Ringrazio il collega Wanderlingh per l’attività svolta in questi anni e mi auguro che la sua collaborazione con il Notiziario continui. Nei primi mesi di quest’anno numerose sono state le iniziative in campo nazionale ed internazionale sia nel settore della luce di sincrotrone sia di neutroni. Nel primo caso la commissione Luce di Sincrotrone dell’INFM ha deciso di sostenere le attività di ricerca presso le linee sperimentali di ELETTRA ed ESRF destinando nuovi finanziamenti sia per le missioni degli utenti sia per borse di dottorato e stages per visiting scientists. Un sostegno finanziario, quantificabile in circa 300 kEuro/anno è anche previsto per i progetti PURS – Progetti Utilizzo Radiazione Sincrotrone – che prevedono lo sviluppo di strumentazione innovativa.

Il Central Laboratory for the Research Council, CCLRC, ed il Consiglio Nazionale delle Ricerche, CNR, hanno recentemente sottoscritto un nuovo accordo per l’utilizzo della sorgente di neutroni impulsati ISIS, confermando una collaborazione tra i due enti, che originariamente risale al 1985, nel settore della spettroscopia di muoni e neutroni.

Questo accordo garantisce alla comunità italiana l’accesso alla sorgente ISIS per lo svolgimento di attività di ricerca sperimentale e rappresenta una importante opportunità per il prosieguo della efficace collaborazione tra ricercatori britannici ed italiani sia nella ricerca di base sia di sviluppo di strumentazione per muoni e neutroni.

Segnaliamo inoltre che il progetto European Spallation Source, ESS, è stato presentato ufficialmente il 15-17 Maggio a Bonn nella suggestiva sede del precedente Parlamento della Repubblica Federale di Germania.

Informazioni sul progetto e sullo svolgimento dell’evento, che ha avuto una grande risonanza anche sui mezzi di informazione, è disponibile sul sito web http://essnts.ess.kfa-juelich.de/Summary_conf/. Per quanto riguarda il progetto ESS durante l’ultimo ESS Council meeting tenutosi a Lund, Svezia, alla fine di Maggio, sia il CNR che il CCLRC hanno inoltre sottoscritto il nuovo Memorandum of Understanding.

Durante la Conferenza di Bonn la Associazione di Spettroscopia di Neutroni Europea ha definito la nomina del suo nuovo presidente, prof. Fabrizio Barocchi, che presiede anche la Società Italiana di Spettroscopia Neutronica. A Fabrizio Barocchi indirizziamo i nostri migliori auguri di un buon lavoro.

Ricordiamo che all’Hotel Capo d’Orso - Località Cala Capra, Palau (SS) a Palau - nel periodo 23 settembre - 3 ottobre 2002 si terrà la VI edizione della Scuola di Spettroscopia Neutronica ‘Francesco Paolo Ricci’. La scuola avrà come tema ‘I neutroni come sonda microscopica di sistemi disordinati’. Questa edizione sarà diretta dal dr.

Ubaldo Bafile (CNR- Fisica Applicata ‘Nello Carrara’) e dal prof. Caterina Petrillo (Politecnico di Milano) e vedrà la partecipazione di docenti dell’ILL (Grenoble), IRI (Delft), HMI (Berlino), Los Alamos (USA), CNR e Università italiane. Gli studenti assisteranno a lezioni di teoria e parteciperanno ad attività sperimentali.

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

2

•

Vol. 7 n. 2 Giugno 2002

S

tarting from this issue the Editorial committee will benefit from the scientific collaboration of dr.

Franco Aliotta who substitutes prof. Ulderico Wanderlingh. I would like to thank Ulderico Wanderlingh his work in these years and I hope that his collaboration with Notiziario will continue.

In the first period of the year there have been several initiatives in the field of synchrotron radiation and neutron scattering in Europe and Italy. The INFM Synchrotron Radiation Board has decided additional support for the research activities based at ELETTRA and ESRF Large Scale Facilities: This will include fundings for user missions, Doctoral fellowship and visiting scientist stages. A budget of about 300 kEuro/year will also be devoted for specific projects, named PURS-Progetti Utilizzo Radiazione Sincrotrone, addressed to the development of novel instrumentation.

The Central Laboratory for the Research Council, CCLRC, and the Italian National Research Council, CNR, have recently agreed to continue the mutual scientific collaboration, started in the year 1985, by signing a new agreement for the use of the pulsed neutron source ISIS. This initiative will guarantee, in the next years, to the neutron and muon scattering Italian community access to ISIS source for scientific research. It also represents an important opportunity for continuing the fruitful scientific collaborations among the British and Italian communities, both in basic research and in the development of muon and neutron instrumentation.

The ESS project proposal was presented officially at the European Source of Science conference in Bonn, in the former House of Parliament of the Federal Republic of Germany from 15-17 May 2002. Information about the ESS project and this event, which deserved much resonance on the press, can be found at the web site http://essnts.ess.kfa-juelich.de/Summary_conf/. Recent news is also the decisions by CNR in Italy and CLRC in the UK to sign the new Memorandum of Understanding ESS which have been announced at the latest ESS Council meeting held in Lund, Sweden, late May. During the Bonn Conference the European Neutron Scattering Association, ENSA, has also nominated its new President, prof. Fabrizio Barocchi, who is also chairing the Italian Neutron Scattering Society, SISN. A warm welcome to Fabrizio Barocchi and best wishes for a fruitful work.

We recall that the VI edition of the Scuola di Spettroscopia Neutronica ‘Francesco Paolo Ricci’ will be held in Località Cala Capra, Palau (SS), in the period September the 23th – October the 3rd. Theme of the school will be ‘The Neutron as a microscopic probe in disordered systems’. Directors of this edition will be dr. Ubaldo Bafile (CNR- Fisica Applicata ‘Nello Carrara’) and prof. Caterina Petrillo (Politecnico di Milano). Teachers will come from ILL (Grenoble), IRI (Delft), HMI (Berlino), Los Alamos (USA), CNR and Italian Universities. Students will be attending lessons on neutron scattering theory and experimental activities.

Carla Andreani

RASSEGNA SCIENTIFICA

Articolo ricevuto in redazione nel mese di Maggio 2002

THE ALOISA BEAMLINE AT ELETTRA F.Bruno1,2, A.Cossaro1, D.Cvetko1,3, L.Floreano1, R.Gotter1, A.Morgante1,2, G.Naletto6, A.Verdini1 , A.Ruocco5, A.Santaniello4, G.Stefani5, G.Tondello6 and F.Tommasini1,2.

1 Laboratorio TASC dell’Istituto Nazionale per la Fisica della Materia, S.S.14 Km 163.5, Basovizza, 34012 Trieste, Italy.

2

Abstract The ALOISA beamline at Elettra is dedicated to the study of the structural and chemical properties of solid surfaces, interfaces and thin overlayers. The custom designed monochromator provides photons with high flux and state of the art energy resolution in an energy range from 150 to 8000 eV. The experimental chamber offers unique versatility in the choice of the detection setup, and the possibility to exploit different investigation techniques on the same system.

We present here a short review of the beamline characteristics and a selection of representative experimental results describing the physical properties which can be investigated at ALOISA.

The main characteristics of ALOISA beamline can be summarized as follows: - a wide photon energy range (150 - 8000 eV) - high photon flux (10 10 to 10 11 ph/s at 0.02% band width) and extremely high energy resolution of the monochromator in the low energy range (200 - 900 eV) - possibility of studying the same system with different spectroscopic and structural investigation techniques in the same experimental chamber - facilities for in situ preparation and monitoring of overlayer and thin film systems - possibility of performing angle resolved multicoincidence (photoelectron - Auger electron) spectroscopy on surfaces (AR-APECS) - wide range of available scattering geometries for unconventional/novel use of the available experimental techniques.

Introduction The chemical and magnetic properties of surfaces, overlayers and thin films are strongly correlated to their local geometrical structure and long range morphology. For this reason, a spectroscopic study of surfaces has to be accompanied by a structural characterization too. Obtaining this complementary piece of information from in situ prepared systems is a difficult task since several experimental techniques operating within the same apparatus are required. This possibility is offered by the ALOISA (Advanced Line for Overlayer Interface and Surface Analysis) beamline of INFM (Istituto Nazionale per la Fisica della Materia), operating at the Elettra storage ring[1]. The ALOISA beamline is designed to perform photoelectron spectroscopy (XPS), absorption spectroscopy, electron coincidence spectroscopy (APECS), photoelectron diffraction (PED), X-ray surface diffraction (XRD) and X-ray reflectivity (XRR) measurements. For this purpose, a monochromator covering a wide energy range was developed and coupled to a dedicated wiggler/undulator insertion device. The monochromator couples a plane mirror - plane grating dispersive system for the 150-2000 eV energy range to a Si(111) channel-cut crystal for the 3 to 8 keV range. Aspherical optics were adopted to reduce the number of optical elements. This optical layout in sagittal focusing configuration together with the absence of entrance slits fully exploits the excellent characteristics of the Elettra Synchrotron.

Dipartimento di Fisica dell’Università di Trieste, Italy.

Department of Physics, University of Ljubljana, Slovenia.

4 ELETTRA Sincrotrone Trieste, Trieste, Italy.

5 Dipartimento di Fisica dell’Università di Roma 3, Italy.

6 Dipartimento di Elettronica e Informatica dell’Università di Padova, Italy.

3

History In 1996 the experimental chamber was tested including the 7 home designed electron analyzers mounted on two independently rotatable frames which, together with the rotation of the whole experimental chamber, allows one to freely explore the sky above the sample for any surface orientation with respect to the X-ray linear polarization. The vacuum chambers of the monochromator were mounted at the end of the year. A preliminary alignment was performed by using a laser source placed inside the machine ring, which gave a rough alignment with the insertion device axis.

The monochromator alignment was completed in 1997 when a dimension of the beam focus at the exit slits of 20 x 150 µm (FWHM) was obtained, in agreement with the design specifications. The refocusing mirror and the experimental chamber were then placed accordingly in order to obtain the beam focus of 20 x150 µm in the centre of the experimental chamber. Along with the spatial beam profile measurements, we also performed the energy calibration and resolution analysis. Energy calibration for various configurations of the PMGM assembly was obtained by acquiring several gas absorption spectra and comparing them to the existing reference spectra.

The photon flux impinging on the sample fulfilled the

Vol. 7 n. 2 Giugno 2002

•

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

3

RASSEGNA SCIENTIFICA

design specifications largely exceeding 10 10 ph/s at 0.02% bandwidth. The world record resolution in the 200-900 eV range was achieved in February. The crystal monochromator was calibrated in the range 3000-8000 eV by measuring solid state absorption spectra. The photon flux was optimised in the whole energy range and it was found to match the design values of 5x1010 ph/s on the sample at the expected resolving power of 7500.

The ALOISA beamline commissioning continued during the first two months of 1998. Surface X-ray diffraction patterns have been measured on different reconstructed surfaces by measuring the current on Si photodiodes.

High intensity surface peaks were detected (up to 105 ph/s) for in-plane diffraction, while the detection method was still limited for out-of-plane diffraction (rod scans) by low counting rates. In fact, the original UHVcompatible energy-resolved photon detector, operating in counting mode, failed to meet the required performances.

Since march 1998 the beamline is open to external users.

During the year 1999 the available experimental techniques have been applied to different system to achieve the state of the art in their application. In particular, the possibility to freely orient the detectors and the surface with respect to the photon beam polarization has been exploited in backward scattering PED experiments to enhance surface relaxation sensitivity, thus achieving bond direction selectivity in measuring atomic distances and photoelectron holography. The combination of forward scattering PED and in-plane XRD has been put forward to become a very effective procedure to study the growing film structures. A major effort has been devoted to optimize the control and acquisition software for PED, APECS and spectroscopy experiments.

At the beginning of the year 2000 a new energy-resolved photon detector has been installed to replace the original system so that out-of-plane XRD has become feasible, which finally completed the set of experimental techniques included in the original project. At the end of the year, the vacuum components of the new HASPES branch line have been delivered. During the following year the new Exit Slit chamber and the deflecting mirror chamber have been installed and optically aligned with a laser.

Beamline characteristics Monochromator performances A schematic layout of the beamline optics is depicted in Fig. 1. The monochromator is a slitless four optical element instrument. It is based on a plane mirror plane grating (PMPG) dispersive element for the low photon energies (150-1500 eV) and on a Si(111) channel cut crystal dispersive element for the high energies (3-8 keV).

The collimating, focusing (paraboloidal mirrors) and re-

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

4

•

Vol. 7 n. 2 Giugno 2002

Fig. 1. Layout of the beamline optics. The collimating and focusing paraboloidal mirrors (P1 and P2), as well as the refocusing toroidal mirror (RT) are placed in sagittally focusing configuration.

focusing mirrors are placed in sagittal focusing configuration in order to reduce the slope error aberration contribution to the degradation of the resolving power. A gas ionization cell provided with a channeltron is mounted downstream the Exit Slit chamber for low energy calibrations. A chamber hosting a second channeltron and a carousel of solid samples is also installed for high energy calibrations. A set of beam attenuators (Al foils) can also be inserted into the beam path in order to avoid saturation of photon detectors operated in counting mode.

During the commissioning of the beamline, we obtained previously unachieved energy resolution for all the measured gas absorption lines in the 200-900 eV range. In fact, some of our overall absorption linewidths (N2 , CO 1s Æ π*) were even narrower than the natural linewidths

Fig. 2. The vibrational splitting of the N2 1s → p* transition, taken at the second diffraction order, with a 50% shadowing of the first mirror. The total linewidth of the first vibrational peak is 123 meV. At that time, a 128 meV width was reported in the literature as the natural linewidth value.

Our experimental data have been fitted to five Voigt functions plus three Lorentzian curves for the fainter peaks. A natural linewidth Γ = 116 ± 2 meV has been obtained.

RASSEGNA SCIENTIFICA

reported in the literature. Very accurate fitting procedures, allowed us to determine new realistic natural linewidths with high accuracy for the reference gases (Ar, N2, CO, Ne), which have been later confirmed by the GAPH beamline at Elettra. Data for N2 are shown in Fig. 2. The corresponding resolving power reaches 10000 at 400-500 eV, while decreasing to 7500 and 5000 at 250 and 900 eV, respectively. This high resolving power is obtained with a high photon flux (in the range of 1010 ph/s).

A 3000 resolving power is given in the whole 200-900 eV range with a photon flux always higher than 1011 ph/s.

Further details can be found on Ref. [2].

ALOISA Experimental station As shown in Fig. 3, the end station of the ALOISA beamline is formed by a preparation chamber and a rotatable experimental chamber that are coupled via a system of two differentially pumped stages and ball bearings. The manipulator, carrying the sample holder, is horizontally mounted and the X-ray beam passes through its head, along its main axis. Inside the experimental chamber, there are two rotating frames which host the detectors.

The differential pumping stages of the two frames are connected to those of the exp./prep. chamber. UltraHigh-Vacuum conditions in the 10-11 mbar range is routinely achieved in the experimental chamber. The experimental chamber and its detector frames can be rotated without affecting the vacuum at the 10-12 mbar level.

The experimental chamber is equipped with several detection systems (Fig. 4): - 7 hemispherical electron analyzers[3] are mounted on two rotating frames inside the UHV chamber. They are dedicated to photoelectron diffraction, angle resolved photoemission and coincidence spectroscopy.

- 2 photon detectors (energy resolved Si PhotoDiodes) are mounted on the Bimodal frame for surface diffraction.

- 1 phosphorum plate coupled with a CCD detector is mounted at the end of the experimental chamber to monitor the specular reflectivity.

- 1 channeltron for total yield absorption spectroscopy is hosted on the Bimodal frame.

- A few photodiodes, working in current acquisition, mode are also mounted within the experimental chamber for reflectivity monitoring and sample alignement.

Fig. 3. The photon beam enters the ALOISA end station from the preparation chamber through the head of the manipulator (yellow) and reaches the sample surface (red). The phosporum plate (yellow) and five electron analyzers (green) are mounted on the Axial frame (brown). Two electron analyzers (green), two photodiodes and one channeltron are hosted on the Bimodal frame (magenta). One photodiode (light blue) is used to monitor the specular reflectivity while the sample is in the preparation chamber, where an MBE flange (dark blue) hosts several evaporation cells.

Vol. 7 n. 2 Giugno 2002

•

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

5

RASSEGNA SCIENTIFICA

Fig. 4. Inside view of the experimental chamber, showing the electron and photon detectors

The manipulator is coaxial to the X-ray beam. In this way the rotations of the manipulator allow one to freely orient the surface plane with respect to the beam polarization (rotation around the beam axis by ± 180°). An azimuthal rotation of ± 90° is available, independently from the surface tilt rotation ± 5° which is used for the choice of the grazing angle on the surface. Liquid Nitrogen cooling of the sample is available as well as a fast insertion system of the sample holder without breaking the UHV conditions.

The experimental chamber rotates around the beam X axis and the two frames follow its rotation. The axial frame rotates around the beam X axis too. When the axial frame rotates its central analyzer always lies in the ZY plane while the other analyzers are placed at ± 18° and ± 36° from the ZY plane.

The bimodal frame rotates around an axis perpendicular to the beam X axis, thus the orientation of its rotation axis (always lying in the ZY plane) also rotates with the whole experimental chamber (see Fig. 5). The Bimodal frame hosts two electron analyzers, which point to the centre of the experimental chamber and are placed 18° one from the other. The two photon detectors are placed at the two external sides of the analyzers, ± 18° further away. The rotating frames, together with the rotating experimental chamber, allow the detectors to explore a wide solid angle above the surface for any orientation with respect to the beam polarization.

HASPES branch line (He Atom Scattering and PhotoEmission Spectroscopy) In 1998, the INFM Synchrotron Light committee has funded the development of a branch line on the ALOISA beamline. The aim of the branch line is to exploit the low energy section of the ALOISA monochromator for allow-

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

6

•

Vol. 7 n. 2 Giugno 2002

ing external users to attach their own experimental chambers; in addition, major overhauling of the ALOISA chamber will be possible while operating the branch line.

The branch line is composed by two elements: a new focusing mirror, placed after the ALOISA focusing mirror and a new Exit Slit (ES) chamber, placed 14 m downstream the new mirror. This large focussing distance has been chosen to obtain a low angular divergence (< 0.3 mrad). In this way no refocusing mirror is required , making easier the coupling of the ES to any experimental apparatus and increasing the total transmission of the branch line. An effective energy range of 150-1200 eV is predicted with the same resolving power and flux of the ALOISA beamline. The beam size at the ES will be of 70 µm, vertical, and 350 µm, horizontal. The branch line components have been delivered at the end of year 2000, and mounted in year 2001. It is expected to be open to external users from 2003.

The Surface Structure Division is also modifying its Helium Atom Scattering (HAS) apparatus in order to use it as end station of the branch line. At the same time, a new hemispherical electron analyzer (150 mm mean radius) has been developed for the HAS apparatus to match the characteristic of the photon beam (both dimension and energy resolution) at the branch line. The analyzer has been realized and tested by the Instrumentation Development Group of the INFM in Rome. An energy resolution of 17 meV has been achieved on Auger spectra from Ar. In the year 2002 the new analyzer will be installed on the HAS apparatus. In addition a new support table has been realized to allow the fine movements for aligning the HAS apparatus along the X-ray beam of the branch line. This project, running within a university collaboration, will allow us to perform in situ both He scattering and photoemission experiments.

Fig. 5. The surface sample (yellow) in Transverse Magnetic polarization is depicted together with the electron analyzers of the Bimodal (green) and Axial frame (red). The rotation axis for the frames and the experimental chamber are also shown.

RASSEGNA SCIENTIFICA

Summary of a selection of experimental results.

In the past three years of user dedicated operation, ALOISA has been successfully used to performed a few dozens of experiments. A large part of these experiments has been carried out in close collaboration between the ALOISA GdR and the users, thus involving the GdR in the data collection, analysis, modelling and final publication of the experiments. Among many systems, the GdR research mainly focused on metal oxides, magnetic multilayers on metals, metal-semiconductor ultrathin films.

The novel optical design of the monochromator has been proven to be very effective. Not only it allows a fast interchange of the two optical devices for the high and low energy range but it has also been proven to reach very high resolution in the low energy range (see Fig.2) maintaining a high photon flux on the sample. A very similar optical design has been recently chosen for some high resolution beamlines of BESSY II. The combination of a multiplicity of structural and spectroscopic techniques has been shown to be very useful for the study of in situ deposited layers. In particular the combination of GXRD and PED allows a very accurate determination of the structure of films which undergo thickness dependent structural transitions. The availability of X-ray reflectivity during deposition allows a very precise measure of the amount of deposited material and therefore a reproducibility of a particular film thickness.

The flexibility of the geometrical arrangement of the ALOISA detection system has allowed to exploit new capabilities of Photoelectron Diffraction experiments for the surface structure determination. A holographic reconstruction of the real space around the emitting atom has been obtained by keeping the electron analyser near the nodal plane of the final state wave function. Moreover a very accurate determination of surface relaxation has been achieved by measuring PED patterns in different geometrical configurations even on systems where no surface core level shifts is observed to discriminate the emission from surface atoms.

The extent of the angular correlation between the photoemitted electrons and the corresponding Auger electrons has been measured by angular resolved APECS. Energy resolved APECS combined with resonant photoemission has been used to study the Auger lineshape respectively off and on resonance, in order to correctly assign different features in the Auger spectra.

Variable polarization PED and Near Node Photoelectron Holography (NNPEH) A number of experiments took advantage from the unique capability of the ALOISA station to freely select the photoemission direction for any orientation of the surface with respect to the beam polarization vector. The

sensitivity of PED to the surface structure can be enhanced by comparing emission patterns collected in different polarization conditions, while holographic reconstruction have proven to reach atomic resolution if the appropriate surface-polarization orientation is chosen.

Recently, PED has been proven to allow the measurement of the surface relaxation by taking photoelectron patterns in systems with a detectable surface core-level shift[4]. The ALOISA experimental set-up offers an alternative route to achieve this goal. By exploiting the light polarization in the photoelectron diffraction experiments it is possible to selectively enhance the contrast between the features originated by the lateral vs vertical structure [5]. At medium/high kinetic energy the PED patterns are known to be dominated by the forward scattering (FS) of the photoelectrons along the direction of close packed rows of the atoms.

When applied to the s-symmetric atomic core levels, this novel measurement method yields information about the interlayer separation if the surface is illuminated by light polarized in Transverse Electric (TE) mode. In fact the FS occurs at grazing emission and higher-order verticalspacing sensitive diffraction peaks, can be more easily evaluated. The reverse occurs in Transverse Magnetic (TM) polarization, where the FS occurs mainly along the surface normal and the sensitivity to the intralayer atomic distance is enhanced. As shown in Fig. 6 for the ZnO(0001) surface case, the method consists in the measurement of full 2Ď&#x20AC; patterns in both TE and TM polarization, and in comparison to the model calculated patterns.

Fig. 6. Schematics of the TE and TM geometrical set-up for the variable PED experiments. The measured 2p patterns of Oxygen 1s photoelectrons (K.E. 309 eV) from the ZnO(0001) surface.

Vol. 7 n. 2 Giugno 2002

â&#x20AC;˘

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

7

RASSEGNA SCIENTIFICA

The variable polarization PED method has been successfully applied to the study of TiO2 (110) surface relaxation (O 1s level and photoelectron kinetic energy ~305 eV), for which theoretical predictions and experimental results are in good agreement. The analysis carried out on the ratio of the TE and TM patterns clearly shows the sensitivity to the surface relaxation of this technique to be at least comparable with the one of SXRD on the same system. Results are summarized in Table 1, where a1 and a2 are structural parameters relevant to the O atoms relaxation on the topmost layer . a1(Å)

a2(Å)

SXRD [6]

0.86 ± 0.13

0.8- 0.9

Ion Scattering [7]

0.8 - 0.9

-

Theoretical prediction [8]

1.05

0.00

Variable polarization PED [9]

0.87 ± 0.04

0.05 ± 0.03

Table 1. Comparison among the values of the structural parameters related to the position of Oxygen atoms in TiO2(110). Further details on the experiments can be found in Ref.[9].

In the last decade, metal oxide surfaces have become the object of a widespread attention within the surface science community. The goal of these investigations is to depict a consistent structure-reactivity relationship for metal oxides, a class of materials which plays a relevant role in many catalytic processes. Among the oxides, the wurtzite-type ZnO is one of the most studied systems and several investigations have been carried out on the (10 -10) and the polar (0001) and (000 -1) surfaces. As far as the (0001) surface relaxation is concerned, literature data give contrasting evidences: from 0.2-0.3 Å inward relaxation of the topmost Zn layer, to ~0.3 - 0.4 Å outward relaxation (from coaxial impact-collision ion scattering data).

The variable polarization PED method has been applied to the determination of Zn0 (0001) surface relaxation, for which a general agreement among the experimental data and theoretical predictions is missing. O1s and Zn 3s 2p patterns in both TE and TM geometry have been collected at an outgoing photoelectron kinetic energy of ~310 eV The O1s χTE/TM modulation pattern has been analysed by means of theoretical multiple scattering (MS) simulations. Data and results are summarized in Fig. 7.

The interlayer distance between the topmost Zn atoms and the underlying O atoms (a) has been varied and the best agreement with the experimental data has been found for a slight inward relaxation of the topmost Zn layer by 0.044 Å. The analysis of the Zn 3s χTE/TM is in progress.

The possibility to obtain holographic reconstruction starting from the photoelectron diffraction pattern would be of great help in determining novel/unknown surface structures. The holographic reconstruction is disturbed by the presence of strong forward scattering (FS) effects in the photoelectron diffraction pattern [10]. FS, being 0th-order diffraction peak, produces spurious features in the real space image and substantially masks the atomic positions. A novel experimental procedure has been suggested[11] and successfully applied at the ALOISA beamline[12,13,14]. It makes use of the linear polarization of the synchrotron light and of the photoemission dipole selection rules to strongly reduce the forward scattering component in the photoelectron diffraction pattern. In fact, by measuring the 2s level emission on Al(111) and keeping the electron detector almost perpendicular to the polarisation direction (“Near Node” geometry) we have shown that the holographic reconstruction is feasible, clearly yielding atomic resolution and the correct nearest neighbours distances. The results are shown in Fig. 8 and 9.

Fig. 7. Left panel : modulation pattern c TE/TM from oxygen 1s (K.E. = 309 eV) level from the ZnO(0001) surface. Central panel : the reliability factor anaylsis resulting from the comparison with the MS model calculations as a function of topmost Zn-O interlayer distance. Right panel: side view along the <1-100> direction.

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

8

•

Vol. 7 n. 2 Giugno 2002

RASSEGNA SCIENTIFICA

Fig. 8. Stereographically projected experimental Al 2s (K.E. 952 eV) photoelectron diffraction patterns from Al(111) single crystal. Comparison between “Far node” (a,d) and “Near Node” (c,f) photoelectron data and their holographic real space reconstructions for the z=0 plane containing the emitter.

Fe(001)[18, 19, 20], with the aim of verifying the possibility of exploiting PED effects in the dichroism signal to disentangle surface and bulk magnetism.

In order to separate experimentally the surface and bulk contributions, ultrathin Co/Fe pseudomorphic overlayers were also grown on the Fe(001) surface. The Fe bulk behaviour was isolated by growing a thin (~3Å) Co overlayer on the clean Fe, creating a system similar to a Co surface on top of a Fe bulk. Then, the chemical identity of bulk and surface atoms was reversed by growing a thicker (9Å) Co layer and a Fe surface layer on top. Results are shown in Fig. 11: of MLDAD modulations are seen to be peculiar of the bulk signal, a fact which confirms their PED nature and can be used as an estimate of the bulk sensitivity of the experiment.

Fig. 9. The holographic 3D image as obtained from the PED data. The atomic environment of the Al 2s emitter at (0,0,0) is shown inside a shell of 4Å radius.

Fig. 10. Geometry for MLDAD experiments. The sample magnetization M is imposed parallel to the beam direction. The polar emission angle β is scanned by rotating the surface normal n around the beam axis.

Magnetic Linear Dichroism in the Angulr Distribution of Photoelectrons (MLDAD) The atomic-like behavior of the photoionization cross section of core levels in solids is remarkably displayed in the observation of linear magnetic dichroism in the angular distribution (MLDAD) of photoelectrons. Structure-related effects are clearly visible as modulations of the dichroism signal, induced by Photoelectron Diffraction, a fact that can be exploited to obtain information from magnetic surfaces[15,16,17]. The experimental setup is sketched in Fig. 10. The chirality of the experiment is determined by the mutual orientation of the photoelectron wavevector k, the sample magnetization M and the beam electric field E. In order to highlight modulations related to the crystal structure of the sample, the polar emission angle is scanned by rotating the sample normal around the beam axis, i.e. with fixed chirality.

We performed measurements on the 3p line in

Structure and morphology of ultrathin metallic layers Fe films on Cu3Au(001) The evaporation of Fe on suitable substrates has been demonstrated to be a valid route to the formation of Fe films with different magnetic properties with respect to the bulk (e.g. antiferromagnetic or superferromagnetic), thanks to the possibility of distorting the Fe lattice cell from its bcc natural form[21,22,23]. Cu3Au(001) is very attracting substrate since it allows one to grow Fe films with different kind of phase structure depending on the substrate temperature, film thickness, surface preparation[24]. We have investigated the Fe/Cu3Au(001) system in a thickness range from 1 to 20 ML by a combined X-ray and photoelectron experiment at the ALOISA beamline[25,26]. In-plane XRD was used to determine the lateral lattice spacing of the growing film, while forward scattering PED polar scans along the main symmetry directions gave us the complementary angular infor-

Vol. 7 n. 2 Giugno 2002

•

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

9

RASSEGNA SCIENTIFICA

was also reported to take place). Finally, at about 15 Å, a third phase nucleates on top of the growing film, with a distorted bcc structure. As the thickness is further increased, the latter phase gradually approaches the Fe bcc bulk structure.

mation to extract the vertical lattice structure (Fig. 12).

We have seen that Fe initially grows with an fcc structure pseudomorphic to the substrate. Au surface segregation has been also observed to affect the pseudomorphic phase in this thickness range. At ~10 Å, a new structural phase is observed on top of the pseudomorphic one (at this thickness a spin reorientation transition

The Sn-Ge bonds in the (3x3)->( √3x√3)R30° phase transition of Sn/Ge(111) Following the debate about the nature of the (3x3) -> (√3x√3)R30° phase transition of 1/3 ML of Sn on Ge(111)[27,28], several studies focused on the structure determination of the two phases[29, 30]. In fact, a change of the atomic structure would have favoured a charge density wave driven transition against an order-disorder one, the former model would have implied a metal to semiconductor transition as well, and even low temperature ferromagnetism. Previous XRD and LEED experiments gave contradictory results, while photoemission experiments suggested the structure to remain unaltered throughout the transition. In fact, two components are observed in the Sn 4d photoemission spectrum which imply the presence of two types of inequivalent Sn atoms in the (3x3) unit cell. This spectrum does not change in the room temperature phase. We studied the Sn/Ge(111) structure by means of energy dependent PED from the Sn 4d spectra[31]. In particular, we exploited the variable scattering geometry offered by ALOISA, to independently measure the bond length between Sn and its nearest neighbour Genn atoms and the Sn vertical height above its next nearest neighbor Gennn atom. This is achieved by orienting either the bond direction either the surface normal along the polarization vector and placing the electron analyzer in the corresponding direction (as depicted in Fig. 13).

We found that the two kind of Sn atoms only differs by their vertical height, while the Sn- Genn bond length is

Fig. 12. Left panel: Fe Auger LMM angular scans along <100> for different Fe coverages on Cu3Au(001) surface. Right panel : (H,0,0) radial scans taken on Fe films of different Fe thicknesses. The pattern from the clean substrate is also reported (yellow markers). The appearance of the α’ and α peaks witnesses the gradual evolution of the Fe film from a pseudomorphic phase to an orthomorphic one. At about 20 Å, the three phases are seen to coexist.

Fig. 13. Geometry used for the determination of the Sn-Ge bond length.

A typical photoemission spectrum is shown in the inset, showing contributions from Sn atoms located in different environments.

Fig. 11. Angular dependence of the amplitude of the dichroic difference spectra in the different Fe/Co systems. The shadowed areas represent the maximum error in the determination of the magnetic signal, i.e. the amplitude (maximum - minimum) of the normalized difference spectrum. In the inset, normal vs off-normal spectra, for the Co/Fe(001) case.

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

10

•

Vol. 7 n. 2 Giugno 2002

RASSEGNA SCIENTIFICA

the same (i.e. the three Genn atoms follow the Sn vertical distortion). The vertical ripple we found (0.3 Å) is in good agreement with both XRD studies and ab initio calculations. In addition, the same structure is also preserved in the room temperature phase.

As a consequence, the transition must be of the orderdisorder type, in full agreement with our findings of a 3state Potts transition obtained by He Atom Scattering study of the (3x3) long range order parameter[32].

Thin Pb films growth on Ge(001) The electronic properties of a thin metal film deviate from the corresponding bulk ones when the film thickness D is comparable with the wavelength of the electrons at the Fermi level [33, 34]. This phenomenon, also known as Quantum Size Effect (QSE), is expected to be at maximum when D is an odd multiple of λF /4, whereas it disappears for D=nλF /2 [35]. Structural variation due to QSE is also expected [36, 37]. We first observed by HAS a structural modification due to QSE during layerby-layer growth of Pb(111) on Ge(001) at 130 K[38]. The measured monoatomic step height was varying as much as 15% around the Pb bulk interlayer separation. The QSE fingerprint is witnessed by the oscillatory variation of the step height. Since HAS is sensitive to the valence electron density of the topmost layer, no direct information on the rearrangement of the interlayer distances inside the Pb film was available. Moreover the mechanism of the layer by layer growth at low temperatures is still unclear. In order to gain complementary insight into the Pb growth at low temperature, we have performed XRR and XRD measurements at the ALOISA beamline. Monitoring the X-ray specular reflectivity during Pb deposition, information about the flatness of the deposited film has been obtained and also the deposition rate has been controlled accurately. The growth oscillations have been measured for a few photon energies and a layer by layer growth regime was observed to set in for coverages higher than 5 ML with extremely low film roughness (see Fig. 14).

For earlier deposition stages the morphology seems to be substantially rough, indicating that between 4-5 ML a transformation in the growth mode takes place. The vertical structure of the film has been explored by scanning the Pb(111) diffraction peak for different vertical momentum transfer (rod scan).We found that Pb atoms aggregates into the crystal structure with at least 3 layer thickness. Simulation of the measured rod scans (Fig.15) indicates that the step height oscillates as shown by HAS measurements but the oscillations are less pronounced amounting to a maximum of 6-7%. This result implies that the valence band electron density oscillates more than the nuclear positions, as could be expected for a quantum size effect, which mainly involves the Fermi level electrons.

Fig. 14. X ray specular reflectivity growth oscillations during Pb deposition on Ge(001) at 140 K. The vertical line marks the transition to the layer by layer growth regime. The oscillation period for different photon energies is also shown.

Fig. 15. Rod scans of the (2,-2,0) reflection from Pb(111). Each data point represent the integrated intensity of an azimuthal scan of the diffracted peak for the given vertical momentum transfer L (in Pb(111) reciprocal lattice units). The first two deposition stages correspond to the 3D growth regime. For the ticker layers layer by layer growth has already set in. Both morphology and vertical structure rearrange at the critical thickness of 5 ML.

Vol. 7 n. 2 Giugno 2002

•

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

11

RASSEGNA SCIENTIFICA

(001) direction of the Ge(100) surface [40]. As shown in Fig.16, intensity modulations arising from diffraction effects are suppressed in the coincidence Auger angular distribution and, when specific emission angles of the photoelectrons are considered, new features appear. We attribute the former effect to enhanced surface specificity of the coincidence technique and the latter to sensitivity of the coincidence measurement to alignment of the core hole state. This last effects reflects in the possibility to discriminate angular and magnetic sublevel in both the Auger and phoelectron source wavfunctions and to measure their energy and/or angular distribution. Finally, by also noting that AR-APECS, by detecting the coincident photoelectron, preserves the chirality of the ionisation event and then opens the possibility to measure dichroic effects in the Auger emission, this new application of the coincidence technique can provide new insight in the study of magnetic systems.

Fig. 16. Pair-wise AR-APECS angular distributions of Ge L3M45M45 Auger electrons measured in coincidence with Ge 2p3/2 core photoelectrons detected in each of the five axial electron energy analyzers. The AED and the coincidence data associated with axial analyzer number 5 are referenced to zero, while the other curves are shifted upward for clarity of presentation

AR-APECS measurements In APECS (Auger Photoelectron Coincidence Spectroscopy) the energy distribution of Auger electron is measured in time coincidence with its associated photoelectron or vice versa. This ensures that both electrons are generated in the same photoexcitation event. In this way an unprecedented discrimination is achieved, such as the capability to isolate individual sites, separate overlapping structures, eliminate uncorrelated secondary electron background, eliminate core hole lifetime broadening [39].

As in conventional spectroscopies, such as AES and XPS, the amount of information is vastly increased when measuring the angular distribution (as in Auger and photoelectron diffraction for instance) in a similar way angular resolved APECS (i.e. AR-APECS) is expected to add an important new level of discrimination.

In one of most recent experiments we have measured the angular distribution of Ge L3M45M45 Auger electrons in coincidence with Ge 2p3/2 core photoelectrons along the

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

12

â&#x20AC;˘

Vol. 7 n. 2 Giugno 2002

Conclusion We presented an overview of the different experimental techniques available at the INFM-ALOISA beamline at ELETTRA. They give access to a large number of physical properties of ultrathin films and surfaces, such as structural and morphological evolution during growth, electronic structure, surface and subsurface magnetism, phase transitions, reduced dimensionality structural effects. In particular, the benefits related to the possibility of combining different techniques on the same apparatus have been highlighted. We have shown a selection of recent results for several systems, as well as the main features of the beamline and of the experimental station.

References 1. Details of the experimental chamber can be found at the web page www.tasc.infm.it/tasc/lds/aloisa/aloisa.html.

2. L. Floreano, G. Naletto, D. Cvetko, R. Gotter, M. Malvezzi, L. Marassi, A. Morgante, A. Santaniello, A. Verdini, F. Tommasini and G. Tondello, Rev. Sci. Instrum. 70 (1999) 3855.

3. R. Gotter, A. Ruocco, A. Morgante, D. Cvetko, L. Floreano, F. Tommasini, and G. Stefani, Nucl. Instrum. Methods A 467468 (2001) 1468.

4. E.D.Tober, R.X.Ynzunza, F.J.Palomares, Z.Wang, Z.Hussain, M.A.Van Hove and C.S.Fadley, Phys. Rev. Lett. 79, 2085 (1997) 5. M. Sambi and G. Granozzi, Surf. Sci. 415, 1007-1015 (1998) 6. G.Charlton, P.B.Howes, C.L.Nicklin, P.Steadman, J.S.G.Taylor, C.A.Muryn, S.P.Harte, J.Mercer, R.McGrath, D.Norman, T.S.Turner and G.Thornton, Phys. Rev. Lett. 78, 495 (1997) 7. B.Hird and R.A.Armstrong, Surf. Sci. 420, L131-L137 (1999) 8. Mramamoorthy, D.Vanderbilt and r.D.King-Smith, Phys.

Rev. B49, 16721 (1994)

RASSEGNA SCIENTIFICA

9. A. Verdini, M. Sambi, F. Bruno, D. Cvetko, M. Della Negra, R. Gotter, L. Floreano, A. Morgante, G.A. Rizzi, G. Granozzi, Surf. Rev. Lett. 6 (1999) 1201.

10. C. S. Fadley, Surf. Sci. Rep. 19, 231 (1993).

11. T. Greber and J. Osterwalder, Chem. Phys. Lett. 256, 653 (1996).

12. J. Wider, F.Baumberger, M.Sambi, R.Gotter, A.Verdini, F.Bruno, D.Cvetko, A.Morgante, T.Greber and J.Osterwalder, Phys. Rev. Lett. 86 (2001) 2337.

13. T. Greber, J. Wider, A. Verdini, A. Morgante, and J. Osterwalder, Europhysics news, Sep./Oct. 2001, p. 172.

14. J. Spence, News & Views Nature 410 (2001) 1037.

15. F. U. Hillebrecht, H. B. Rose, T. Kinoshita, Y. U. Idzerda, G. van der Laan, R. Denecke, and L. Ley, Phys. Rev. Lett. 75, 2883 (1995).

16 R.Schellenberg, E.Kisker, A.Fanelsa, F.U.Hillebrecht, J.G.Menchero, A.P.Kaduwela, C.S.Fadley, M.A. Van Hove, Phys. Rev. B57 14310 (1998) .

17. G.Panaccione, F.Sirotti, G.Rossi, Solid State Comm. 113 (2000) 373 18. F. Bruno, D. Cvetko, L. Floreano, R. Gotter, A. Morgante, A. Verdini, G. Panaccione, M. Sacchi, P. Torelli, and G. Rossi, J. Magn. Magn. Mater. 233 (2001) 123.

19. F. Bruno, R. Gotter, A.Morgante, A. Verdini, G. Panaccione, M. Sacchi, F. Sirotti, P. Torelli, Physica B, in press.

20. F. Bruno, G. Panaccione, A. Verdini, R. Gotter, L. Floreano, P. Torelli, M. Sacchi, F. Sirotti, A. Morgante and G. Rossi, accepted for publication on Phys. Rev. B. 21. M. Wuttig, B. Feldmann and T. Flores, Surf. Sci. 331-333, 659 (1995).

22. G.C. Gazzadi, F. Bruno, R. Capelli, L. Pasquali, S. Nannarone, Phys. Rev. B 65 (2002) 205417.

23. S. Tacchi, F. Bruno, G. Carlotti, D. Cvetko, L. Floreano, G. Gubbiotti, M. Madami, A. Morgante, and A. Verdini, Surf.

Sci., in press.

24. P.M. Marcus and F. Jona, Surf. Rev. and Lett. 1, 15 (1994).

25. F. Bruno, D. Cvetko, L. Floreano, R. Gotter, C. Mannori, L. Mattera, R. Moroni, S. Prandi, S. Terreni, A. Verdini and M. Canepa, Appl. Surf. Sci. 162-163 (2000) 340.

26. F. Bruno, S. Terreni, L. Floreano, A. Cossaro, D. Cvetko, P. Luches, L. Mattera, A. Morgante, R. Moroni, M. Repetto, A. Verdini, and M. Canepa, Phys. Rev. B, in press, condmat/0103458.

27. J.M. Carpinelli, H.H. Weitering, E.W. Plummer, and R. Stumpf, Nature 381, 398 (1996).

28. A. Mascaraque, J. Avila, J. Alvarez, M.C. Asensio, S. Ferrer, and A.G. Michel, Phys. Rev. Lett. 82, 2524 (1999).

29. O. Bunk, J.H. Zeysing, G. Falkenberg, R.L. Johnson, M. Nielsen, M.M. Nielsen, and R. Feidenhansâ&#x20AC;&#x2122;l, Phys. Rev. Lett.

83, 2226 (1999).

30. J. Zhang, Ismail, P.J. Rous, A.P. Baddorf, and E.W. Plummer, Phys. Rev. B 60, 2860 (1999).

31. L. Petaccia, L. Floreano, A. Goldoni, D. Cvetko, A. Morgante, L. Grill, A. Verdini, G. Comelli, G. Paolucci and S. Modesti, Rev. B 64 (2001) 193410, cond-mat/0103358.

32. L. Floreano, D. Cvetko, G. Bavdek, M. Benes, and A. Morgante, Phys. Rev. B 64 (2001) 075405 33. R.C.Jaklevic, J.Lambe, M.Mikkor and W.C.Vassell, Phys. Rev. Lett. 26, 89 (1971) 34. M.Jalochowski, E.Bauer, H. Knoppe and G.Lilienkamp, Phys. Rev. B 45, 13607 (1992) 35. F.K.Shulte, Surf. Sci. 55, 427 (1976) 36. P.J.Feibelman, Phys. Rev. B 27, 1991 (1983) 37. S.Ciraci and I.P.Batra, Phys. Rev. B 33, 4294 (1986) 38. A. Crottini, D. Cvetko, L. Floreano, R. Gotter, A. Morgante and F. Tommasini, Phys. Rev. Lett. 79 (1997) 1527 39. G.A. Sawatzky, in Auger Electron Spectroscopy, edited by C. L. Bryant and R. P. Messmer (Academic, Boston, 1988), p. 167 40. R. Gotter, A. Ruocco, M.T. Butterfield, S. Iacobucci, G. Stefani and R.A. Bartynski, submitted.

Vol. 7 n. 2 Giugno 2002

â&#x20AC;˘

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

13

RASSEGNA SCIENTIFICA

Articolo ricevuto in redazione nel mese di Novembre 2001

SIMULATION OF THE UPGRADE OF THE BACKSCATTERING SPECTROMETER IN13 AT ILL C. Mondellia, M. Béeb, A. Deriuc and F. Natalia (a) Istituto Nazionale per la Fisica della Materia, OGG, CRG IN13 Institut Laue Langevin B.P. 156, F-38042 Grenoble Cedex 9

(b)Université Joseph Fourier, Domaine Universitaire, B.P. 82 Saint Martin D'Héres-Giéres 38042 Grenoble Cedex, France (c)Universitá degli Studi di Parma, Parco area delle Scienze 7/A, I-43100 Parma,Italy

Abstract Ray tracing becomes more and more a very helpful tool in the project of new instruments as well as in the upgrade of existing instruments.

The availability of different packages and codes and of large libraries has contributed to the generalized use of Monte Carlo simulations in the frame of instrument projects.

In the specific case of IN13 a progressive upgrade of the instrument is planned in order to improve the incident flux - as in the present configuration the performance of the instrument is overall limited by the low incident flux - and also to increase the instrument versatility. In this way, different possibilities other than the present standard configuration will be available in order to allow the user to define the best compromise between flux, energy resolution and Q-range for each experiment.

The first step of this project consists of simulating the instrument and the different modifications envisaged in order to verify our ideas and to determine which are the most promising modifications and the possible degradation of certain characteristics of the instrument. This a particularly important point, as one has to preserve the characteristics that make of IN13 a particularly suited spectrometer for the study of the local dynamics of soft matter, such as polymers and biological systems, e.g. a large momentum transfer range (now 0.3<Q(Å-1)<5.5) and an energy resolution of few µeV. Thus we have performed Monte Carlo simulations of the primary spectrometer and our results together with data from experimental tests show that IN13 could be modified in order to obtain a gain in neutron flux up to a factor of 12.

one needs to determine only the position of inelastic tunneling peaks and not the peak shape and measurements at large Q are not limited by the Debye-Waller factor because they are generally carried out at low temperatures and using single crystals, so reducing the problem represented by the Bragg scattering from the sample.

However, since 1998 the instrument is dedicated mainly to the study of the dynamics of biological systems, a growing field in physics. In this frame the neutron flux is critical as the samples are typically small and the analysis of the shape of the quasi-elastic signal is very important. Additionally, the lack of single crystals makes relevant the problem represented by Bragg reflections and most of the experiments are performed close to room temperature so posing also the problem of the attenuation at large Q due to the Debye-Waller factor.

In this new context, a project of renovation and redesign of the instrument was started together with the discussions at ILL for renovating the H24 guide, where IN13 is located, using supermirrors.

The basic idea of this upgrade is to give the instrument a flexible character, by allowing reversible modifications to be easily carried out in order to adapt it to the optimum compromise between all the relevant experimental parameters, namely flux, energy resolution, Q-range and Q-resolution [2].

The simulation of the instrument is particularly important to study the effects of the different envisaged transformations on both flux and energy resolution at the sample, and analyze the consequences of any future modification. A particular effort is needed to improve the flux on the sample, but unfortunately, it is no possible to increase the flux without loosing energy or Q-resolution. However the users of IN13 typically need different characteristics because they have very different interests; so often one or more of these parameters can be relaxed to increase the neutron flux. Thus, a first proposition to increase the neutron flux was to set the analyzer plates out of the exact BS geometry by moving the detector into a position where it could not receive the neutrons directly scattered by the sample. In that case the resolution is worsened, as one deviates from exact BS geometry, but the chopper – which is used to allow to separate the direct scattering from the neutrons that

Introduction In the eighties the study of tunneling effects was very popular and the back-scattering (BS) spectrometer IN13 at the Institut Laue Langevin (ILL) was specially designed for this kind of experiments [1]. Thus, it was built in order to achieve a good energy resolution with a large Q-range, being these the more important characteristics for such experiments. The drawback is that this could be obtained only at the expense of intensity. This is not a severe limitation in the study of the tunneling, as

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

14

•

Vol. 7 n. 2 Giugno 2002

RASSEGNA SCIENTIFICA

come from the analyzers and has a duty cycle of 33% – is not needed anymore, so the numbers of neutrons reaching the sample can be increased by a factor of 3. Simulations confirmed by experimental tests have shown that this is feasible: We find that moving the analyzers 1 degree out of the BS-geometry changes the energy resolution from 8 µeV to 15 µeV (FWHM), which can be still an acceptable resolution in many cases. Unfortunately, larger deviations from perfect BS give rise to an unacceptably large resolution function, so the geometrical con-

Fig. 1. Possible set ups of IN13 moving two of the analyzer plates on the negative scattering angles. a) Image of the present configuration of IN13; b) New set up of the analyzers and detectors allowing to install some of the analyzers plates on the side of the negative scattering angles to obtain a gain of the flux of a factor 2 for the corresponding Q values.

straints make possible this out of BS option only for the study of small samples. However, this is the case in many biological experiments, so this could be still a very helpful possibility.

Apart from the energy resolution, another problem posed by the stopping of the chopper is the presence of other harmonics in the neutron beam: λ/2, λ/3, ... which are normally eliminated by a suitable choice of the chopper’s duty cycle. Luckily this does not seem to be a serious problem as the relative amount of l/2 measured in the incident beam is only of the order of 10% and this ratio is certainly smaller for the neutrons impinging on the detectors because of the selective reflectivity of the analyzers.

One of the most important and distinctive feature of IN13 is its large Q-range (0.3<Q(Å-1)<5.5).

The instrument is equipped with seven analyzer plates and three small angle circular analyzers (at the moment not used in perfect BS geometry) covering the scattering angle range 5.8 < 2Θ< 156º.

The instrumental configuration is fixed and a large part of the high Q analyzers is shielded with cadmium to avoid the Bragg peaks arising from the aluminum walls of the cryostat. This results in a lose of flux of about 20%, a loss which increases when the sample itself scatters coherently as further angles then have to be covered. Additionally, for liquid and disordered systems close to room temperature there is a strong decrease in the scattered intensity at large Q values because of the Debye-Waller attenuation, so in many cases the larger angles are not used at all. Thus, we are studying a modification of the instrument that would allow moving some of the analyzers to the side of negative scattering angles.

In this way the corresponding scattering angles would be measured with both ±2Θ analyzers, and there would be an increase in intensity by a factor 2 for the corresponding momentum transfers.

In order to achieve this goal several modifications of the spectrometer are required: At present there is a single bank of 32 detectors and the set of analyzers at small angles is fixed, thus preventing the rotation of the analyzers plates on the side of the carousel [3] (see Fig. 1a). We will have to rebuild the bank of detectors (dividing it in 7 independent blocs) and to modify the carousel and the system of fixation of the small angle analyzers in order to permit the rotation of the analyzer plates along the carousel to the chosen position (see Fig. 1b). This version of the instrument would allow three different setups - shown in Fig. 2 - and the possibility to record twice the same signal either at small or large scattering angles or maintaining the same angular as now (each angle being measured only once).

Another improvement under study is the replacement of the neutron guide H24. The present guide is coated with

Vol. 7 n. 2 Giugno 2002

•

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

15

RASSEGNA SCIENTIFICA

Fig. 2. Sketch of the three different possible choices for the analyzers set up. The new version of the instrument could make possible to record twice the same signal either for the small or for the large scattering angles as well as to have the same angular coverage as now (full angular coverage, each angle being measured only once).

nickel and its reflectivity has decreased over its lifetime so the outcoming flux now is 30% lower than it was 20 years ago [4]. Therefore a simple replacement of the Nicoated guides will provide a subsequent increasing on neutron intensity. Moreover, the possibility of equipping the guide with supermirrors (SM) and changing its dimensions is also being considered. The cross section of the neutron beam could change from 3x20 cm2 to 4.5x20 cm2. This decision concerns the three instruments present along the guide: IN3, IN13 and D10 and each instrumental team has to study the conditions under which it could fully benefit from this operation. For IN13 a particular emphasis has to be put on the size and divergence of the beam because they can influence noticeably the energy and Q resolution. Therefore, the effects of those changes need to be accurately evaluated by means of Monte Carlo simulations, as shown in the next section.

Further modifications are planned for the upgrade; such as the substitution of the detector tubes with new tubes with higher pressure and efficiency, the setting of the small angle circular analyzers to perfect BS geometry by using a new type of concentric detectors, a new cryostat, the addition of new analyzers crystals, etc. However, these points are still under study and they will not be presented in more detail in this communication.

Results of Monte Carlo simulations A first step of the upgrade consists in simulating the instrument in order to determine the effect on both flux and energy resolution brought by the installation of supermirrors in the neutron guide. Thus, we have performed a series of Monte Carlo simulations of the primary spectrometer using the McStas code [5]. This package has been developed to facilitate the simulation of all kind of neutron instruments and it is a very suitable tool to study and project new spectrometers or modify exist-

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

16

•

Vol. 7 n. 2 Giugno 2002

ing instruments. The general scheme of IN13 is shown in Fig. 3. In order to simulate realistically IN13 we use a flat source with a gaussian divergence mimicking the neutron beam that comes from the H24 guide and reaches the monochromator. This source sends the neutrons to a guide formed by three segments: the first is straight and is L1=3.3 m long; the second one is curved (curvature radius R=27 Km), L2=74.5 m; and the third is straight with L3=6.3 m. Their cross section is constant (3x20 cm2), except for the last segment, where the height is reduced to 12.5 cm because of the presence of the IN3 spectrometer along the guide. The beam reaches then the monochromator, which is a CaF2 crystal (422) formed by three different crystals with a mean mosaicity of η= 2.5’. The monochromatic beam is reflected to the sample position by a deflector that consists in a pyrolitic graphite (004) crystal (13.4x5 cm2) formed by 9 lamellae η= 45’ (a picture of the present deflector is shown in Fig. 4).

Finally, at the sample position we have put several monitors with the same dimensions of a typical sample holder, i.e. 3x4 cm2, in order to check how the characteristics of the guide (reflectivity and dimensions) affect the energy resolution and flux.

The gain in flux is calculated as the ratio between the intensity for a given reflectivity and guide dimensions and the flux for the present guide, which is simulated taking into account the lost of reflectivity due to aging. Thus, a Ni coated guide with a reflectivity of R0=0.96 instead of 1 and width=30 mm was considered.

The results are given in Table 1, where one can see that the best result obtained without substantial modification

Fig. 3. Schematic diagram of the IN13 layout.

RASSEGNA SCIENTIFICA

Fig. 4. Present deflector of IN13. It is composed from nine lamellae of pyrolitic graphite (004) crystal (13.4x5 cm2, η= 45’)

of the instrument is reached by using a supermirror guide (SMG) m=3 with a guide 30 mm wide. On the other side, the replacement of the guide by a wider one is not so effective as forecasted. In effect, the data given in Table1 show that the increase of the guide cross section from 4.5x13.5 cm2 to 3.0x13.5 cm2 does not result in a corresponding increase of the neutron intensity at the sample position, indicating that the extra 50% of neutrons gained by the larger cross section is lost before arriving to the sample. In order to understand the origin of this loss we have monitored what happens at the guide exit, the monochromator, the deflector and the sample position. The results show that all the extra neutrons arrive to the monochromator but afterwards a big percentage is lost between the latter and the deflector. This is due to the fact that the deflector width (5 cm) is not large enough to recuperate the larger beam coming from the monochromator. In fact the beam width at the deflector is ~ 5 cm for the 3 cm guide but increases to 8 cm for the 4.5 cm guide. This is due to the high beam divergence produced by the supermirror guides, as can be seen in Fig. 5, where a comparison between the beam size on the deflector is shown for the cases of 30 mm and 45 mm guides. Besides this, some neutrons are also lost between

Fig. 5. Image of the neutron beam after being backscattered on the monochromator. Both pictures have been obtained using a position sensitive monitor with the dimensions of the present deflector and situated at 90 cm from the monochromator (i.e. 12 cm before the deflector). The top figure corresponds to the simulation results obtained with the 30 mm guide and the bottom figure to the 45 mm guide.

the deflector and the sample, as the width of the deflected neutron beam is larger than 3 cm, which is the standard sample size. While this is true in both cases the beam width is slightly larger for the w=4.5 cm guide than for the w=3 cm guide, resulting in a bigger loss and producing the final result that the intensity at the sample position is practically the same. We have checked the effect of using a larger deflector (8 cm wide), but although the results are slightly better, a lot of neutrons are still lost because of the divergence of the beam. Therefore, a first important result from our simulations is that in order to profit from having a wider neutron guide several changes should be envisaged. First, the IN13 deflector should be reviewed, making it wider (at least 8 cm) and focusing not only vertically but also horizontally. Other project under study is the possibility of redesigning the last segment of the neutron guide to make it focusing or of adding a focusing guide between the monochromator and the deflector. Further simulations are currently used to test all of these ideas.

Vol. 7 n. 2 Giugno 2002

•

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

17

RASSEGNA SCIENTIFICA

Guide width (mm)

Ni

58Ni

SMG(m=2)

SMG(m=3)

30

1.23

1.31

1.79

1.85

45

1.23

1.34

1.80

1.88

45*

1.34

1.48

2.09

2.19

Table 1 Gain of the flux at the sample position for different guide reflectivity. The reported quantity is the ratio between the number of neutrons reaching the sample position for a new ideal guide and the present situation which corresponds to an aged Ni coated guide (see text). The first two rows show the results obtained simulating the present deflector (5 cm wide), the latest row marked by a star shows the results obtained when a new deflector 8 cm wide is used in the simulation.

The effects of the change of the guide coating on the energy resolution function were also studied, because it is important that the gain of the flux occurs without a too big detriment of the energy resolution.

The FWHM of the energy distributions of the neutrons arriving at the sample does not change significantly (see Fig.6), but their shapes are different. The tails of the curves are more extended for the case of the SMG, which can be a disadvantage for the study of phenomena that show very small quasi-elastic broadening. On the other side it looks acceptable for most of experiments.

Conclusions The aim of the upgrade of IN13 is to obtain a very flexible instrument, which can be adapted to each experiment in order to obtain the best compromise between flux, energy resolution, Q-range and Q-resolution.

In order to optimize the choice of the neutron guide and to obtain a reliable estimation of the gain in intensity and the effect on the energy resolution, Monte Carlo simulations of the primary spectrometer were performed. The results show that the neutron intensity on the sample can be multiplied by a factor of ~2 by using a SMG (either with m=2 or m=3). This could be combined with a new set up of the analyzers that will permit to multiply it by a factor 2 in a chosen Q-range. Furthermore, when the quantity of sample is small it is possible to use a configuration of the instrument where the analyzers are aligned slightly out of BS and the chopper can be stopped, which would result in an additional gain by a factor 3. Thus a total gain of about one order of magnitude can be expected, at least in special cases. Although such an increase would only be possible for small samples, this is the usual case with biological systems and it is precisely then that the higher flux is more needed.

In the future, further simulations including the secondary spectrometer will be performed to determine the consequences of any other modifications.

Acknowledgments Particular thanks go to M. A. González from the ILL for the help given on the use of the McStas simulation package and useful discussions.

References

Fig. 6. Energy resolution functions for the different guides proposed (30mm wide, 108 events were generated at the neutron source.

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

18

•

Vol. 7 n. 2 Giugno 2002

1. M. Prager and A. Heidemann, ILL Internal report, Grenoble 1995.

2. M.Bée, “Dynamical characteristics of biological systems from neutron scattering experiments and relation to biological function.” CRG IN13 Internal report, Grenoble 2001.

3. See the IN13 home page:www.ill.fr/YellowBook/IN13 4. W. Kaiser, Flux measurements performed on the H24 guide indicate that the reflectivity has decreased over 30 years of operation, resulting in a loss of flux of around 30%. Private communication.

5. K.Lefman and K.Nielsen, Neutron news 10/3, 20 (1999).

RASSEGNA SCIENTIFICA

Articolo ricevuto in redazione nel mese diMaggio 2002

X-RAY INTERFERENCE MEASURES THE STRUCTURAL CHANGES OF THE MYOSIN MOTOR IN MUSCLE WITH Å RESOLUTION M. Reconditi, G. Piazzesi, M. Linari, L. Lucii, Y.-B. Sun*, P. Boesecke‡, T. Narayanan‡, M. Irving* and V. Lombardi

Dipartimento di Scienze Fisiologiche, Università di Firenze, Viale G.B. Morgagni 63, I-50134 Firenze, Italy *School of Biomedical Sciences, King’s College London, Guy’s Campus, London SE1 1UL, UK ‡ESRF, BP 220, 38043 Grenoble, France

Abstract Force and shortening in muscle are thought to be driven by a conformational change (the working stroke) in the myosin head domains that cross-link the myosin and actin filaments. However definitive evidence linking the structural changes, seen in isolated myosin head fragments by crystallography, to the motor action in the preserved structure has not yet been produced. The improved brightness and collimation of the X-ray beam at beam line ID2 at the European Synchrotron Radiation Facility (ESRF, Grenoble, France) led to the development of a new technique that can measure the axial motions of myosin heads in muscle with Å sensitivity. The method depends on X-ray interference between the two arrays of myosin heads in each bipolar myosin filament, which superimposes a finely spaced fringe pattern onto the ~14.5 nm X-ray reflection (M3) originating from the axial repeat of the myosin heads along the thick filaments [1].

We used this method to study the motions of myosin heads in single intact fibres from frog muscle during the synchronous execution of the working stroke elicited by rapid decreases in length superimposed on an isometric contraction [2]. During the isometric contraction the M3 reflection is composed of two major peaks with axial spacings 14.46 and 14.67 nm; the ratio of the intensities of the high angle peak to the low angle peak, IHA/ILA, is about 0.8. Shortening steps reduce the value of IHA/ILA to a minimum value of ~0.3, as expected for displacement of the myosin heads towards the centre of the myosin filament. The results indicate that tilting of the lever arm of the myosin head is the mechanism that drives force generation and up to 10 nm filament sliding.

(thin) filament, 1 µm long, originates from the Z line bounding the sarcomeres and partially overlaps with the myosin filament. The myosin molecule is a dimer with an elongated portion, the tail, made by the coiled coil alfa helices of the two monomers, which lies on the thick filament, and two large globular portions, the myosin heads, that emerge from the thick filament. To form the thick filament, the tails assemble in an anti-parallel manner starting from the M line, so that myosin heads are oriented in opposite directions in the two halves of the filament and a region of ~ 0.2 µm around the M line is free of myosin heads (bare zone, Fig. 1B). Crowns of three pairs of heads emerge from the thick filament every ~14.5 nm (Fig. 1C). Successive crowns are rotated by 40° forming a three-stranded helix with ~ 43 nm period. Actin monomers (diameter 5.5 nm), with axial periodicity of 2.73 nm, are arranged in a double stranded helix in the thin filament with pitch 37 nm.

Force and shortening in muscle are generated by cyclic interactions of the myosin heads with the adjacent thin filaments in the region of overlap. During the interaction the myosin head undergoes a conformational change (the working stroke) that, depending on the mechanical conditions, can generate a force of several pN or an axial displacement of the actin filament toward the centre of the sarcomere of several nm. The work produced is accounted for by the free energy of the hydrolysis of ATP on the catalytic site of the myosin head.

Structure of the sarcomere In the striated muscle the contractile proteins, myosin and actin, are organised into filaments that overlap in axially repeating structural units called sarcomeres (Fig. 1A). In each sarcomere the myosin (thick) filament, about 1.6 µm long, is made of two symmetrical halves, each containing about 150 myosin molecules, connected at the centre of the sarcomere by the M line. The actin

A crystallographic model of the working stroke in the myosin head Biochemical studies of contractile proteins in solution [3] provided evidence that the energy liberation by the actomyosin complex is mainly associated with the release of the ATP hydrolysis products, phosphate and ADP. In the absence of ATP, the nucleotide-free myosin head strongly bound to actin is responsible for the rigor state of the muscle. The description of the crystallographic structure of the nucleotide-free myosin head [4, 5] allowed development of a model of the working stroke with atomic resolution [6]. The myosin head consists of a large globu-

Vol. 7 n. 2 Giugno 2002

•

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

19

RASSEGNA SCIENTIFICA

Fig. 1. Sarcomere structure. A. Longitudinal section of frog sartorious muscle as seen by electron microscopy (top) together with the diagram showing the overlapping actin (red) and myosin (blue) filaments (adapted from H.E. Huxley, 1972 [27]). B. Antiparallel arrangement of the myosin dimers in the two halves of the thick filament, with a bare zone free from heads in the centre. The origin of the bare zone is indicated. C. The myosin filament (cyan) with the protruding myosin heads (blue) overlapped with a hexagonal net of six actin filaments (red). The myosin heads emerge axially as triplets with 14.5 nm periodicity. In each triplet the pairs of heads are separated azimuthally by 120° and adjacent triplets are rotated by 40°, thus forming a threestranded helix with period ~ 43 nm. Each actin filament is made by monomers assembled in a double stranded helix with period ~ 37 nm.

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

20

•

Vol. 7 n. 2 Giugno 2002

RASSEGNA SCIENTIFICA

Fig. 2. Atomic model of the working stroke. Grey/brown, actin filament; red, myosin catalytic domain (residues 1–707); green, converter domain (residues 711–781); blue, long helix (residues 781–843); yellow, essential light chain; magenta, regulatory light chain. The lower myosin structure (N-free, nucleotide free, light blue long helix) shows skeletal muscle myosin bound to actin in a conformation determined by cryo-electron microscopy in the absence of ATP; the upper myosin structure (ADP•AlF4-) is derived from a smooth muscle myosin fragment with ADP•AlF4- in the active site. The catalytic domain of the ADP•AlF4- bound structure was superimposed on that of the nucleotide-free structure; only the nucleotide-free catalytic domain is shown. The orientation of the light chain domain in the ADP•AlF4- structure was determined by superimposing residues 711–731 and 738–780 of the converter–light chain domain complex from the nucleotide-free structure onto the corresponding converter residues in the ADP•AlF4- bound structure, assuming that the converter–light chain complex moves as a rigid body. The Z-line of the half-sarcomere is at the bottom. Residue numbers refer to chicken skeletal myosin. From Irving et al., 2000 [18].

Vol. 7 n. 2 Giugno 2002

•

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

21

RASSEGNA SCIENTIFICA

lar catalytic domain (CD, residues 1-707) that contains both the actin binding site and the catalytic site and a slender neck region, the light chain binding domain (LCD, residues 707-843), formed by an alfa helix 9.5 nm long that extends from the catalytic domain to the junction with the rod and is stabilised by binding the two light chains. Comparison of the crystallographic structure of a fragment of the myosin head, complexed with an analogue of the ATP hydrolysis products (ADP.AlF4-, [7]), with that of the nucleotide-free head [5] (Fig. 2) suggests that the release of Pi from the active site induces inter-domain molecular rearrangements resulting in a ~70° tilting of the LCD about the CD firmly attached to actin.

Due to the length of LCD acting as a lever arm the tilting motion is amplified into ~ 11 nm axial displacements of the head-rod junction. This value is twice the length step measured for one myosin encounter with actin in most single molecule experiments [8, 9], but is similar to the value estimated with the rapid force transients that follow step changes in sarcomere length superimposed on isometrically contracting intact muscle fibres [10, 11].

SAXS measurements of the working stroke The function of myosin depends on the interaction between conformational changes in the motor and external force or motion as it occurs in the native system (the sarcomere) when the head is attached to actin, and this cannot be reproduced in crystallographic studies. Due to the quasi crystalline arrangement of the motor proteins in the three-dimensional lattice of a muscle, small-angle Xray scattering (SAXS) can be used to record the conformational changes in the myosin motor, at a lower spatial resolution than that of crystallography, but in the native environment for the motor function. In particular the intensity of the strong third order meridional reflection (IM3), originating from the ~14.5 nm axial repeat of the myosin heads, is sensitive to the changes in mass density projection of the myosin heads onto the filament that accompany the execution of the working stroke.

IM3 changes can be interpreted in terms of detailed conformational changes by using the crystallographic models. In Fig. 3 IM3 is used to measure the tilting angle between the LCD and the CD in the atomic model of Fig. 2. The horizontal axis in Fig. 3 shows the displacement (z) of the tip of the lever arm (the head-rod junction) produced by the tilting, thus it is related to the sliding between the thick and thin filament. At z= 0, that corresponds to the nucleotide-free structure, IM3 has a value similar to that at z= 10.6 nm, corresponding to the ADP.AlF4- structure. IM3 is higher for intermediate tilting and is maximum for z= 5.4 nm, when the axial coordinates of the centroids of the LCD and of the CD coincide and the axial density distribution is the narrowest.

Thus changes in IM3 can be used to define the conforma-

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

22

•

Vol. 7 n. 2 Giugno 2002

tional changes during the myosin working stroke.

In a normal contraction working strokes occur asynchronously, since the ensemble of myosin heads is spread out through the various steps of the chemo-mechanical transduction cycle. However, in intact single fibres isolated from frog muscle, the working stroke in the attached myosin heads can be synchronized by superimposing, on the isometric contraction, step length perturbations controlled at the level of the half-sarcomere [10, 12]. The drop in force simultaneous with a shortening step (phase 1 of Huxley and Simmons force transient), due to the elasticity of attached myosin heads and myofilaments, is followed by a quick recovery of force (complete within 1-2 ms, phase 2), which represents the mechanical manifestation of the myosin working stroke.

By repetitive synchronisation of the working stroke using trains of steps of the appropriate frequency (Fig. 4A), it is possible to preserve an adequate signal:noise and reduce the time per frame of X-ray signal to the 100 µs range necessary to resolve the changes of IM3 during the elastic response and the subsequent execution of the working stroke [13-15]. As shown in Fig. 4, a step release of 5.5 nm per half-sarcomere (B) produces a little (6 ± 6%, mean ± SD) increase of IM3 (D) during the elastic drop in force to 0.25 T0 (C). IM3 shows a large decrease during the quick recovery: 1 ms after the release, when the force has recovered to 0.66 T0, IM3 is reduced to ~0.5 of its isometric value. The little change of IM3 during the elastic response suggests that z moves across the peak of the IM3-z relation in Fig. 3. The synchronous execution of the working stroke moves the experimental point downhill along the ascending limb of the IM3-z relation. Following a step stretch of the same size as the release, ap-

Fig. 3. Dependence of the intensity of the M3 X-ray reflection (IM3) on z.

Filled circle indicates the nucleotide-free crystallographic conformation and filled square indicates the ADP•AlF4- structure. Filled triangles, filled diamond, open circle and open square correspond to five time points in the experiment in Fig. 4. Adapted from Irving et al., 2000 [18].

RASSEGNA SCIENTIFICA

plied 1 ms after the shortening step, the force rises to about 1.5 T0 and then recovers towards its isometric value (Fig. 4C). IM3 increases during the stretch (Fig. 4D), due to the elastic response of the heads that brings z back towards the isometric value (Fig. 3), and then undergoes a small decrease, during the force recovery associated with the reversal of the working stroke, due to the movement of z across the peak of the IM3-z relation. The best fit of the data with the IM3-z curve shows that during isometric contraction the LCD is tilted by 60° from the filament axis, that is 40 ° (or 7 nm, filled triangle in Fig. 3) from the nucleotide-free conformation.

Though the SAXS data are consistent with the tilting lever arm model, the measurements of the extent and of the direction of the working stroke from the intensity

Fig. 4. Changes in force and the intensity of the M3 X-ray reflection (IM3) produced by a shortening step and stretch separated by 1 ms during active contraction. A, Superimposed slow time base force records in the presence and absence of the 40 length change cycles imposed at 50 ms intervals. Fibre cross-sectional area was 22,200 µm2 and its length was 6.75 mm; the mean sarcomere length in the 2.10 mm segment was 2.09 µm.

Changes in segment length (B) and force (C), in the same fibre as panel (A), sampled at 10 µs intervals, in the first part of the first length change cycle, and IM3 (D, filled circles, in 100 µs time bins) from 402 tetani in 14 fibres; the noise is predominantly due to the small number of diffracted X-ray photons in each time bin. The length change measured 1 ms after the start of the shortening step in these fibres was 6.36±1.12 nm hs-1 (mean±SD). Dashed line: IM3 without applied length changes in the same fibres (48 tetani). Open circles were calculated from the relation in Fig. 3 with ziso=7.2 nm. From Irving et al., 2000 [18].

changes of the M3 reflection are strongly model-dependent. Moreover, the intensity of the reflection depends also on other parameters, such as the number of contributing heads and their axial and conformational disorder. For these reasons, a completely different mechanism for force generation cannot be excluded: the decrease in intensity of the M3 reflection during the quick recovery following a shortening step could be interpreted as well with increase in conformational disorder due to rapid detachment of a fraction of heads after their spring has been unloaded, followed by rapid reattachment in a strained conformation.

The X-ray interference effect With a highly collimated beam such as that of ID2/SAXS beamline at ESRF (Grenoble, France [16]), the myosinbased meridional reflections show a fine structure (Fig. 5; [1]), due to the interference between the two arrays of myosin heads in each thick filament, an effect first described in the whole muscle at rest by Huxley and Brown [17]. Each half of the thick filament (Fig. 6B, blue) contains an array of 49 layers of heads (red) with regular spacing d (~14.5 nm). This array generates the M3 X-ray reflection (Fig. 6C, red). The two arrays in each thick filament generate a sinusoidal interference modulation (blue) with a spatial frequency equal to the reciprocal of

Fig. 5. Axial X-ray diffraction patterns from a single muscle fibre at rest (A) and at the plateau of an isometric tetanus (B). Sarcomere length, 2.07 µm; 6 s exposure time in both conditions. The axial pattern at rest shows a series of reflections that index on the ~ 43 nm quasi-helical periodicity of the myosin heads in the thick filaments [17]. The reflection indicated by the arrow (M3) corresponds to the ~ 14.5 nm axial repeat of the myosin heads and remains intense also during the isometric contraction.

Vol. 7 n. 2 Giugno 2002

•

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

23

RASSEGNA SCIENTIFICA

the centre-to-centre distance between the arrays (L, the interference distance, ~900 nm). The structure of the thick filament in Fig. 6B can be approximated by a model where each layer of myosin heads is reduced to a point diffractor at the position of its centre of mass and can be defined by the convolution of an array of N points with spacing d with two points separated by L. The Fourier Transform (F.T.) of an array of N points spaced d is:

F.T. (Z) =

sin( NπZd ) sin(πZd )

(1)

where Z is the reciprocal space parameter.

The phase of the F.T. is set to zero by choosing the centre of mass of the array as the origin of the coordinates in the real space. The F.T. of the whole structure is the product of the F.T. of the two separate structures, and, once squared, it gives the scattered intensity distribution along the meridional direction: sin( NπZd ) 2 sin(2πZL) 2 sin( NπZd ) 2 2 I(Z) =   ⋅  =  4 cos (πZL)  sin(πZd )   sin(πZL)   sin(πZd ) 

(2)

Fig. 6. Interference fine structure of the M3 reflection and its dependence on axial motion of the myosin heads. A, D. 2D patterns in the region of the M3 reflection, collected on the Image Plate detector, at the isometric plateau (A), and during the quick force recovery following a shortening step (D). B, E. Scheme of the two arrays of myosin heads (red) in each myosin filament (blue) with the LCD tilting as during the isometric contraction (B) and following a shortening step (E). Actin filament in green.

C, F. Axial X-ray intensity distribution (black) generated by the sampling of the M3 reflection (red) by the interference function (blue). To fit the axial intensity distributions from A and B the interference distance L is set to 866 nm (C) and 863 nm (F) respectively.

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

24

•

Vol. 7 n. 2 Giugno 2002

The first factor of the last term in eq. (2) represents the reflection originating from the axial repeat in each array (Fig. 6B, red), and the second factor is the interference function (blue). When, as in the case of the myosin filament, L is much larger than d (L ~ 900 nm ~ 60 d), the reflection is finely sampled by the interference function (Fig. 6C, black).

In an isometrically contracting muscle fibre at 4 °C the M3 reflection, due to the 14.57 nm spacing of 49 layers of heads in each array, is split into two closely spaced peaks, at 14.47 nm and 14.66 nm (Fig. 6A). The ratio of intensity of the high angle peak to that of the low angle peak (IHA/ILA) is ~0.8 [1], showing that the interference distance is close to an odd multiple of half the 14.57 nm spacing.

Due to the bipolar arrangement of the myosin heads in the two halves of the thick filament, when actin-attached myosin heads execute the working stroke that pulls the actin filaments towards the centre of the sarcomere, the centre of mass of the heads, and hence the centre of mass of each array, also moves towards the centre of the sarcomere (Fig. 6E). Consequently, the interference distance L reduces and the sinusoidal intensity distribution shifts to a higher reciprocal spacing (rightward in Fig. 6F), decreasing the relative intensity of the high angle peak of the sampled M3 reflection. If the fibre is stretched so that the actin filament and the catalytic domains attached to it are pulled away from the centre of the sarcomere, L and the relative intensity of the M3 high angle peak increase accordingly. Thus the interference method is able to resolve the direction of the movement, independent of a structural model for the head. The high order (~60th) by which the interference function samples the M3 reflection increases the sensitivity of the method to Å scale movements of the centroid of myosin heads. In Fig. 7 it

Fig. 7. Relation between IHA/ILA and L, calculated with eq. (2) with N=49 and d=14.57 nm. Triangle and circle correspond to the axial intensity distribution in C and F of Fig. 6.

RASSEGNA SCIENTIFICA

Fig. 8. Changes in interference fine structure of the M3 X-ray reflection produced by rapid shortening. A, Length change (nm/hs), and force normalized by isometric force T0. Fibre cross-sectional area, 27,300 µm2; T0, 293 kN m-2; sarcomere length, 2.13 µm. B, Axial X-ray intensity distribution of the M3 reflection normalized to that of the lower angle peak. Colours denote the periods T0, T1 and T2 shown in A. Adapted from Piazzesi et al., 2002 [2].

Vol. 7 n. 2 Giugno 2002

•

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

25

RASSEGNA SCIENTIFICA

is shown how the ratio IHA/ILA varies with L based on eq.

(2), for the given d (14.57 nm) and N (49). Unlike the total intensity of the reflection, the interference effect is insensitive to changes in the fraction or conformational disorder of attached heads. These features altogether make Xray interference the most powerful tool for testing, in the native system, the tilting LCD model of force generation versus rapid attachment/detachment of the heads.

Interference measurement of the working stroke The structural changes in the head accompanying the mechanical working stroke were measured in a series of experiments at ID2/SAXS (ESRF) by recording the interference changes during the elastic response and the subsequent quick force recovery following shortening steps ranging from 2 to 9 nm per half-sarcomere [2]. Intensity profiles of the M3 reflection were collected in a 2-ms time frame before the length step (Fig. 8, A, B, T0, green), in a 100-µs time frame close to the end of phase 1 (T1, red) and in a 2 ms time frame near the end of phase 2 (T 2, blue). The shortening step reduced the value of IHA/ILA and shifted both peaks to a higher angle (Fig. 6D and 8B), as expected for displacement of the two arrays

Fig. 9. Changes in IHA/ILA following shortening steps of different sizes. Red circles (T1) and blue triangles (T2) are the means ± SEM for n=3–6 fibres, except for the T1 point at -7 nm per half-sarcomere (n=1). Green square denotes the value for the 2-ms period before the length step (T0, Fig. 8); orange diamond is the value from contractions without imposed length steps. The lines were calculated from the simulations described in the text: red, T1; blue, T2. Continuous lines indicate that only one head of each myosin responds to the length step; red dashed line (T1) indicates that all heads in the fibre respond to the step; blue dashed line (T2) indicates the rapid detachment/attachment model. From Piazzesi et al., 2002 [2].

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

26

•

Vol. 7 n. 2 Giugno 2002

of actin-attached myosin heads towards the centre of the sarcomere. Most of the change occurred at the end of the shortening step (T1) and only a small further reduction occurred during the subsequent rapid force recovery phase (T1 to T2 transition). The reduction is larger the larger the size of the step, but saturates for steps larger than 7 nm (Fig. 9).

The experimental values of IHA/ILA were used to calculate the interference distance L, using the theoretical intensity distributions described above (Fig 6). Eq. 2 applies exactly if each layer of myosin heads can be considered as a point diffractor, but parallel analysis using the mass projection of the atomic model of the myosin head in the isometric conformation [5, 18] gave the same values of I HA/I LA [1]. Thus the change in L responsible for the change in IHA/ILA can be used as an estimate of the average displacement (∆C) of the centres of mass of the myosin heads with respect to their attachment to the myosin filament (the tip of the LCD). As shown in Fig. 10, ∆C (negative for displacements towards the center of the thick filament) was proportional to the size of the shortening step for steps up to 7 nm, but was about 5 times smaller than the imposed filament sliding. The value of ∆C at T2 (Fig. 10, blue triangles) was similar to that at T1 (red circles). This result is consistent with models in which the quick force recovery is due to the working stroke in myosin heads that remain attached to actin in phase 2. In fact, in models without working stroke, where the force is simply proportional to the strain in the heads, force recovery in phase 2 would be accompanied by heads binding to new actin sites farther from the centre of the myosin filament, and thus by an increase of ∆C. To make a quantitative interpretation of the observed axial motions of the myosin heads during the elastic phase 1 response, we must take into account the compliances of the actin filament (0.26%/T 0, [15, 19]) and of the myosin filament (0.14%/T0, [2, 15, 20, 21]). With these parameters the axial displacements of each layer of myosin heads along the filament during the elastic response to length steps of different size can be calculated.

The displacements are then used in the fine structure simulation (see Methods), where each layer of myosin heads is represented by the atomic model with the CD in its nucleotide-free conformation [5, 6] and a variable tilt between the CD and the LCD. The changes in IHA/ILA calculated with this simulation are shown by the red dashed line in Fig. 9 and are much larger than the observed changes (red circles). The reduced changes in interference fine structure during the length step can be explained if a population of heads do not respond to the length step, although they have sufficient axial order to contribute to the M3 reflection. These heads can be the partner heads of those attached to actin. In this case the attached head imposes order on its partner since they

RASSEGNA SCIENTIFICA

are joined at the head-rod junction. The changes in IHA/ILA during the elastic response, calculated with the addition of the partner heads (Fig. 9, red continuous line), gave a good fit to the observed changes.

According to the working stroke model, during the quick force recovery the tilt of the attached heads changes to account for the changes in the strain of actin and myosin filaments and heads themselves. The calculated values for T2 interference changes (Fig. 9, blue continuous line) are close to the observed data (blue triangles) even if the fit is not perfect. In contrast, the interference changes calculated with the rapid attachment/detachment model (blue dashed line) are clearly inconsistent with the results of the experiment, because in this case the centres of mass are expected to move farther from the centre of the thick filament as new strained myosin heads are formed during rapid force recovery.

The imperfect fit of the working stroke model to the observed fine structure at T2 may be explained by a small fraction of heads detaching during phase 2, as already suggested on the basis of changes in stiffness [12] and total intensity of the M3 reflection [18] following a 5 nm shortening step.

In conclusion, the X-ray interference changes measured during the elastic response and the subsequent rapid force recovery following shortening steps of different size (2-9 nm) provide definitive evidence for a mecha-

Fig. 10. Axial motions (∆C) of myosin head centroids with respect to their myosin filament attachments. The value of ∆C was obtained for each fibre and condition by fitting experimental values of IHA/ILA. A negative value of ∆C denotes motion towards the centre of the myosin filament.

See Fig. 9 for definition of symbols. The lines were obtained by linear regression of all individual fibre data except the T2 points in the -9 nm per half-sarcomere. From Piazzesi et al., 2002 [2].

nism of force generation based on a ~10 nm working stroke in the myosin heads attached to actin, and against the idea of rapid detachment of myosin heads followed by rapid reattachment to new actin monomers.

Methods Experimental protocol.

Single fibres were dissected from the lateral head of the tibialis anterior muscle of Rana temporaria, and mounted horizontally on a microscope stage in a chamber containing Ringer’s solution. One of the fibre tendons was attached to a loudspeaker coil motor and the other to a capacitance gauge force transducer via aluminium foil clips [22]. The resting sarcomere length was set to 2.1 µm and fibre length, width and depth were measured. The temperature was controlled at 4∞C. Fibres were electrically stimulated for 2.3 s at 18-25 Hz. After 0.3 s of isometric contraction, a series of 40 shortening/stretch cycles was imposed with a 4 ms interval between shortening and stretch and a 50-ms cycle time [14]. Sarcomere length in a 1-2 mm segment near the centre of the fibre was measured continuously with a striation follower [23].

The stage carrying the muscle fibre, motor and transducer was mounted on the high brilliance X-ray beamline ID2 at ESRF (Grenoble, France, [16]). The X-ray flux was up to 2 x 1013 photons s-1 at wavelength 0.1 nm, and the full width at half-maximum (FWHM) of the X-ray beam was ca 0.1 mm vertically and 0.6 mm horizontally. Muscle fibres were mounted with their long axes vertical to optimise spatial resolution. The X-ray path through the Ringer’s solution was reduced to about 600 µm by placing two mica windows close to the fibre. The timing of X-ray exposures was controlled with 10-µs precision using two electromagnetic shutters in series, and monitored using a pin diode on the backstop of the X-ray camera. X-ray data were collected on A3-size storage phosphor Image Plates (Molecular Dynamics) mounted in an evacuated camera tube 9.85 m from the fibre. Image plates were scanned off-line at nominal spatial resolution 100-µm with a Molecular Dynamics 840 scanner.

The point spread function of the X-ray camera/scanner combination was measured by recording 50-µs exposures with the X-ray beam attenuated by 50-µm rhodium, and was well fitted by a Gaussian function with FWHM 320 µm in the vertical direction.

Fibres were stimulated at 4 min intervals. After each period of stimulation the fibre was moved along its axis by 100-250 µm to spread the effects of radiation damage.

Length change cycles were imposed during stimulation using the cyclical protocol described above. For 100 µs X-ray exposures, diffraction data were typically accumulated from 40 length steps in each of 20 contractions with the unattenuated X-ray beam (total exposure 80 ms per

Vol. 7 n. 2 Giugno 2002

•

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

27

RASSEGNA SCIENTIFICA

image plate). For 2 ms exposures, data were collected from 40 length steps in each of 4 contractions with the beam attenuated by a factor of 4. The X-ray pattern during isometric contraction was recorded with 200 ms exposure in each of 4 contractions with 7x beam attenuation. The total X-ray exposure per fibre was typically equivalent to 0.5 s of the unattenuated beam. Experiments were terminated by failure of excitation-contraction coupling, and up to this point X-ray and mechanical responses were stable. X-ray data are presented from 18 fibres with cross-sectional area 22,500 ± 5,800 µm2 (SD) X-ray data analysis.

X-ray diffraction patterns were analysed with the programs HV (A. Stewart, Brandeis), Fit2D (A. Hammersley, ESRF) and Peakfit (SPSS Science). Patterns were aligned and centred using the 1,0 equatorial reflections. The background under the axial X-ray reflections was subtracted using HV. The axial intensity distribution was calculated by radial integration from ± 1/64 nm-1. The intensity distribution in the region of the M3 reflection was fitted by two Gaussian peaks using Peakfit, with the position, height and width of each peak as free parameters.

The centre of mass of the M3 reflection was then calculated as the intensity-weighted mean of that of the two component peaks. Axial spacings were calibrated by assuming the M3 spacing in the resting fibre to be 14.340 nm [24], or that in active isometric contraction to be 14.573 nm [1].

Simulation of the interference fine structure The intensity profile of the M3 reflection was calculated as the F.T. of the axial mass distribution of the myosin heads. Each myosin filament is represented as two arrays of 49 layers of heads symmetrical with respect to the centre of the filament. The axial mass projection of each layer was calculated from crystallographic data with the CD (heavy chain residues 1-707) of the head in the nucleotide-free conformation [5] and the LCD (heavy chain residues 707-843 and both light chains) tilted around the CD/LCD junction (residue 707). In the simulation shown in Fig. 9 we have used a distributed filament compliance formalism [19, 25, 26] to calculate the force and strain distributions along the myosin and actin filaments. The strain in the myosin heads, represented by the tilt of the LCD with respect to the actin-bound CD, is assumed to be uniform during the steady force developed in the isometric contraction. Following the length step the tilt (and the strain) of the heads changes according to the change in strain of myosin and actin filaments. In the working stroke model the distribution of head strain after a length step is calculated under the constraint that the sarcomere length remains constant during the quick force recovery. Simulation using the

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

28

•

Vol. 7 n. 2 Giugno 2002

rapid detachment/attachment model assumes that the total fraction of heads attached to actin remains constant and that the average head strain is proportional to force.

With either models, there is no detectable difference if, instead of using heads with different strains according to the distributed filament compliance, we use heads uniformly spaced and with the same angle of tilt corresponding to the average conformation in each phase of the mechanical response. In this case the two arrays of heads on the myosin filament can be represented as two heads (or two pairs of heads) with the same tilt of the LCD, one the mirror image of the other, and with their centres of mass separated by L, convoluted with an array of 49 points with spacing d. The predicted intensity distribution is then the product of the intensity distribution from the array of points centred at the position 1/d in the reciprocal space (see eq. 1), and the intensity distribution from the two heads (or pairs of heads), that carries information on both the conformation of the heads and the position of the centres of mass and may be calculated with the equation: n 2 I(Z) ∝ ∑ cos[2πZ ( x i + D / 2)]    i= 1 

(3)

where D is the distance between the head-rod junctions of the two heads and xi is the coordinate of the ith residue constituting the molecule, relative to the head-rod junction. The position of the centre of mass of the head relative to the head-rod junction is: n

C=

∑ x /n i

i= 1

(4)

and L= D + 2C. Changes of the interference distance L are due to either changes in the strain of the myosin filament, which affects D, or changes in the tilting of the LCD, which affects C. In the first case D and, by approximation, L change by the same proportion as d, so that (Eq. 2) the fine structure of the reflection does not change. Thus only changes in L due to axial motion of the heads change the fine structure of the reflection.

References 1. Linari, M., Piazzesi, G., Dobbie, I., Koubassova, N., Reconditi, M., Narayanan, T., Diat, O., Irving, M., Lombardi, V., Proc.

Natl. Acad. Sci. USA 97, 7226-7231 (2000) 2. Piazzesi, G., Reconditi, M., Linari, M., Lucii, L., Sun, Y.-B., Narayanan, T., Boesecke, P., Lombardi, V., Irving, M. Nature 415, 659-662 (2002) 3. Lymn, R.W. and Taylor, E.W. Biochem. 10, 4617-4624 (1971) 4. Rayment, I., Rypniewski, W.R., Schmidt-Base, K., Smith, R.,

RASSEGNA SCIENTIFICA

Tomchick, D.R., Benning, M.M., Winkelmann, D.A., Wesenberg, G., Holden, H.M. Science 261, 50-58 (1993) 5. Rayment, I., Holden, H.M., Whittaker, M., Yohn, C.B., Lorenz, M., Holmes, K.C., Milligan, R.A. Science 261, 58-65 (1993) 6. Geeves, M.A. and Holmes, K.C. Annu. Rev. Biochem. 68, 687728 7. Dominguez, R., Freyzon, Y., Trybus, K.M. and Cohen, C. Cell 94, 559-571 (1998) 8. Molloy, J.E., Burns, J.E., Kendrick-Jones, J., Tregear, R.T., White, D.C. Nature 378, 209-212 (1995) 9. Mehta, A.D., Finer, J.T. and Spudich, J.A. Proc. Natl. Acad.

Sci. USA 94, 7927-7931 (1997) 10. Huxley, A.F. and Simmons, R.M. Nature 233, 533-538 (1971) 11. Piazzesi, G. and Lombardi, V. Biophys. J. 68, 1966-1979 (1995) 12. Lombardi, V., Piazzesi, G, and Linari, M. Nature 355, 638-641 (1992) 13. Irving, M., Lombardi, V., Piazzesi, G. and Ferenczi, M.A. Nature 357, 156-158 (1992) 14. Lombardi, V., Piazzesi, G., Ferenczi, M.A., Thirlwell, H., Dobbie, I., Irving, M. Nature 374, 553-555 (1995) 15. Dobbie, I., Linari, M., Piazzesi, G., Reconditi, M., Koubassova, N., Ferenczi, M.A., Lombardi, V., Irving, M. Nature 396, 383-387 (1998) 16. Boesecke, P., Diat, O. and Rasmussen, B. Rev. Sci. Instrum. 66, 1636-1638 (1995)

17. Huxley, H.E. and Brown W. J. Mol. Biol. 30, 383-434 (1967) 18. Irving, M., Piazzesi, G., Lucii, L., Sun, Y.-B., Harford, J.J., Dobbie, I.M., Ferenczi, M.A., Reconditi, M., Lombardi, V. Nature Struct. Biol. 7, 482-485 (2000) 19. Linari, M., Dobbie, I., Reconditi, M., Koubassova, N., Irving, M., Piazzesi, G., Lombardi, V. Biophys. J. 74, 2459-2473 (1998) 20. Wakabayashi, K., Sugimoto, Y., Tanaka, H., Ueno, Y., Takezawa, Y., Amemiya, Y. Biophys. J. 67, 2422-2435 (1994) 21. Huxley, H.E., Stewart, A., Sosa, H. and Irving, T. Biophys. J. 67, 2411-2421 (1994) 22. Lombardi, V. and Piazzesi, G. J. Physiol. (Lond.) 431, 141-171 (1990) 23. Huxley, A.F., Lombardi, V. and Peachey, L.D. J. Physiol.

(Lond.) 317, 12P-13P (1981) 24. Haselgrove, J.C. J. Mol. Biol. 92, 113-143 (1975) 25. Thorson, J.W. and White, D.C.S. Biophys. J. 9, 360-390 (1969) 26. Ford, L.E., Huxley, A.F. and Simmons, R.M. J. Physiol. (Lond.)

311, 219-249 (1981) 27. Huxley, H.E. In The structure and function of muscle, Academic Press Inc. (1972)

Supported by MURST, CNR and Telethon (Italy), MRC (UK), EU, EMBL and ESRF.

Vol. 7 n. 2 Giugno 2002

â&#x20AC;˘

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

29

RASSEGNA SCIENTIFICA

Articolo ricevuto in redazione nel mese di Maggio 2002

THE CONTRIBUTION OF NEUTRON SCATTERING TO CULTURAL HERITAGE RESEARCH R. Rinaldi1, G. Artioli2, W. Kockelmann3, A. Kirfel4, S. Siano5 1 Dipartimento di Scienze della Terra, Università di Perugia, I-06100 Perugia, Italy 2 Dipartimento di Scienze della Terra, Università di Milano, Via Botticelli 32, I-20133 Milano, Italy

3

Abstract The discovery of ancient artefacts and artworks that bear witness to our cultural heritage typically raises a variety of questions: from the correct determination of their historical and cultural time-frame, the place and method of production, to the choice of treatments and conditions for restoration and preservation. A large variety of chemical, physical and microstructural techniques are currently employed to characterise objects of cultural significance, indeed the same techniques that are generally applied to studies in the mineralogical and material sciences, and which deal with the characterisation of solid, generally inorganic matter such as; mineral, stone, ceramic, glass, metal, and their derivates.

Neutrons, as opposed to X-rays, are the best probe for examining the interior of thick samples. Neutron analysis, which is intrinsically non-invasive, is both unique and complementary to more conventional techniques.

When sampling is not possible, neutron methods provide chemical, phase specific, and microstructural information from undisturbed large volumes. Furthermore, comparison with artificially produced materials, such as metals and alloys, can also be effectively exploited in order to obtain indirect information on the manufacturing techniques of the objects under investigation.

Specifically, neutron diffraction at the most modern and powerful neutron sources and, in the future, at the new generation of ESS-type sources, is providing and will provide invaluable information on cultural heritage objects that must not be damaged by cutting, drilling, scraping etc. Data can be collected from large, intact objects of almost any shape, and the experimental set-up is both simple and free from sample movements. The many-fold increment in signal and resolution afforded by the newly designed sources and instruments, will allow element sensitive small volume phase identification and quantification, detailed crystal structure analysis of the constituent phases, and direct imaging in two- and three-dimensions by imaging and tomography techniques also enhanced by energy-tuning procedures.

These methods can certainly provide a clearer picture of the technological, commercial and, more generally, his-

torical and archaeological aspects of the sample. With a view towards preservation, they can provide invaluable information regarding the choice of restoration and conservation procedures.

As with the mineral and Earth sciences, the potential of neutron scattering is only recently being realised in the fields of archaeometry and preservation of cultural heritage. With the availability of modern and future neutron sources there is much to look forward to with the opening of new avenues in this field of study.

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

30

•

Vol. 7 n. 2 Giugno 2002

University of Bonn, Forschungszentrum Jülich, D-52425 Jülich, Germany and ISIS Facility, UK 4 Mineralogisch-Petrologisches Institut, Universität Bonn, D-53115 Bonn, Germany 5 CNR - Istituto Fisica Applicata “Nello Carrara”, I-50127 Firenze, Italy

1. Introduction Most frequently, archaeometric determinations of artefacts are obtained by methods such as electron microbeam analysis and imaging, x-ray fluorescence and neutron activation analysis. These are predominantly chemical probe methods; complementary information can be obtained by phase analysis through diffraction methods (x-ray, electron or neutron). However, most of these methods are invasive in one form or another as they require destructive sampling techniques such as coring, transversal sectioning, or even powdering some portion of the sample. When dealing with objects of cultural heritage and historical significance (prehistorical artefacts, priceless artworks, palaeontological material) sample destruction or damage is clearly unacceptable.

Consequently, much current research is aimed at developing non-destructive, diagnostic techniques.

Moreover, extrapolation of results taken from microsamples to represent large objects or bulk samples is strongly questionable. What is required is a non-invasive diagnostic technique that provides fundamental information on composition and structure from anywhere within an antique object (i.e. penetrating deeply into the sample as well as probing a large part of its volume) which can be ideally represented by present-day, and especially next generation, neutron scattering facilities.

2. Neutrons in archaeometry and conservation Microstructure, phase identification/quantification and texture analysis of archaeological objects by neutron diffraction has only recently been undertaken, but the po-

RASSEGNA SCIENTIFICA

tential applications of such powerful techniques span many fields of interest within archaeometry, conservation, archaeological and natural history research, ranging from routine fingerprinting to complex conservation problems. The standard diagnostic tools used today for ceramics, glass, paintings, and metals are not suitable for the characterisation of inhomogeneities at both the microscopic and macroscopic scale, that would provide information on thermal profiles, element distribution, mixing, and mechanical properties developed during manufacture. For instance, segregation, dendritic heterogeneity, degree of hardening and twinning, crystallinity, all represent fundamental aspects required for the determination of the historical and cultural background of archaeological findings, to correctly reconstruct their history, the manufacturing technology and to evaluate sample deterioration.

Non-destructiveness in bulk.

The non-destructive nature of neutron scattering experiments makes the technique well suited for handling large, undisturbed samples and rare, unique objects, both natural and man-made, that encompasses materials as diverse as, for instance: sediment layers, rocks, fossils, bones, ceramic, plasters, paintings, glass, metals and alloys. The importance of good grain statistics demands measurements from large samples. In stone diagnostics in particular, where grains on the order of one mm3 are not rare, again large samples are often required. Furthermore, a generalised interpretation of analytical results from small portions of a large artwork be it stone, ceramic, glass, metal or other, can be highly misleading. Neutrons offer a non-destructive diagnostic technique providing fundamental information on the composition and structure of an antique object, extending deeply into its interior as well as on a large part of its volume.

Direct imaging, radiography, tomography.

Neutron penetration can be advantageously exploited for neutron imaging to determine the inner features of materials and artefacts, such as composition, density and phase distributions, beyond the reach of less penetrating probes, with specific applications in archaeology and preservation.

At present most neutron imaging is performed either by simple neutron radiography, which exploits the absorption contrast of different elements in the object to obtain two- and three- dimensional projections (Winkler et al., 2002), or by neutron-induced gamma activation, which also allows chemical analysis by measuring the decay time of the activated species.

These techniques can be very advantageously used to investigate stone, ceramic and glass materials but also frescoes and painting materials such as recently performed

at HMI Berlin for the correct attribution of some of Rembrandtâ&#x20AC;&#x2122;s works from the Berlin-Dahlem Museum (Preussischer Kulturbesitz).

It is expected that the neutron flux supplied by the next generation of ESS-type source will enhance the quality of imaging of artworks through the use of energy-tuned narrow (but still intense) neutron beams, so that the resonant absorption of specific nuclei and the prompt emission of gamma rays by short lived isotopes may be used for a 2-dimensional (radiography) or 3-dimensional (tomography) analysis of the successive paint layers as well as of bulkier materials. The enhancement of the attenuation coefficient due to coherent Bragg scattering can be exploited to provide an element sensitive signature in radiography and tomography (Kardjilov et al., 2002).

3. Stone materials Surface reactivity and water content.

The specific problem of stone degradation (i.e. in historical buildings) needs detailed characterisation of the constituent materials and textures, including porosity and fluid contents. The methods and techniques are identical to those used in the investigation of modern building materials such as cements and concretes.

Water, carbon dioxide and sulphate ions are largely responsible for the degradation of natural building stones even when present in very low concentrations; the detailed study of such systems on an atomic scale can solely be addressed by the unique capabilities of modern neutron facilities. The breakdown, weathering and transformation of minerals generally involves the migration of hydrogen through the mineral surface and into the subsurface of the crystals. This implies volume increase, may induce oxidation and can be coupled with other ion exchange reactions or the freeze-thaw cycling. All of these processes change the physical properties of the near-surface region of the minerals. As these weathering reactions occur at the mineral/fluid or mineral/biota interface, a fundamental understanding of mineral surface reactivity requires the application of light element surface sensitive spectroscopy and diffraction. Furthermore, reactive H2O, CO2 and SO4 must be neutralised prior to preservation.

Commonly, X-rays are used in the reflective mode to investigate mineral surfaces, however, neutrons are far superior to X-rays for direct probing of protons and deuterons. Furthermore, rapid high-resolution, high-intensity neutron spectroscopy, reflectivity and diffraction are required to study the dynamics and to generate models of mineral hydration, molecular binding and ion exchange involving iso- and quasi-iso-electronic species (e.g. Ti4+-Ca2+-K+; K+-Cl-, Na+-Mg2+-Al3+-Si4+, or Fe2+-Mn2+) where X-rays fail to provide the necessary scattering contrast for discrimination.

Vol. 7 n. 2 Giugno 2002

â&#x20AC;˘

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

31

RASSEGNA SCIENTIFICA

Fig. 1. Perugia, Fontana Maggiore after restoration of the marble and limestone decorations. Conservation and preservation problems still need to be addressed. (Photo courtesy of B. Moroni and G. Poli, Perugia)

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

32

â&#x20AC;˘

Vol. 7 n. 2 Giugno 2002

RASSEGNA SCIENTIFICA

Fig. 2. Time of Flight neutron diffraction yields information on intact objects such as of this small black-gloss Athenian-style wine jug (approx. 7cm high) of unknown origin. A secondary collimation device or a neutron absorber inside the vessel prevents neutron scattering from the back wall of the vase. The diffraction patterns were simultaneously obtained with detectors at forward (a) and backscattering (b) angles.

The olpe was kindly provided by Dr. A..J.N.W. Prag, The Manchester Museum, Manchester University, UK. The photo is the property of The Manchester Museum.

(Kockelmann et al., 2000).

Prior to any surface treatment of degrading stones and sculptures in monuments and buildings, a bulk, quantitative assessment of the residual H, OH and H2O content must be performed. This analysis must be non-destructive and capable of handling/exploring large dense samples while simultaneously detecting weak and/or very subtle signals. Only the next generation of neutron sources and instrumentation will enable studies on very low concentrations present in such samples.

Diffraction methods in archaeometry and restoration.

Archaeological research based on phase, microstructure and texture analysis of artefacts and stone materials us-

ing neutrons is also relatively new but offers great potential. A review of the work done by these techniques in the field of natural stone materials can be found in Schäfer (2002). Diffraction techniques are important for helping to date excavation sites, to establish trading patterns, to determine cultural exchange between regions, to elucidate historic and regional abundance, trading networks and to help identify the original source of raw materials. Phase and microstructural characterisation of ancient objects by diffraction methods can provide suggestions as to the specific manufacturing techniques that were used. Diffraction studies, besides the issues of source materials may also address the alteration or cor-

Vol. 7 n. 2 Giugno 2002

â&#x20AC;˘

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

33

RASSEGNA SCIENTIFICA

Fig. 3. Time of Flight diffraction patterns and Rietveld analyses from data collected at ROTAX, ISIS, on Brühl and Siegburg ceramics (top). Characterisation of pottery fragments by mineral phase fraction ratios mullite/quartz (full columns), indicative of firing temperatures. The B* samples from a 13th century pottery series from Brühl are characterised by a high cristobalite content (hatched columns). (Kockelmann et al., 2002).

Fig. 4. Top: side (left) and bottom (right) view of an Etruscan olpe (400 BC, Museum of Chiusi, Italy) different parts of which have been analysed by quantitative multiphase analysis using TOF neutron diffraction (ISIS, ROTAX): (1) bottom wall, (2) side wall, (3) handle and (4) repair patch. Different peak positions indicate different tin contents while different peak widths indicate different microstructures (top, centre). Bottom: diffraction patterns and Rietveld analyses of side wall (2) and repair patch (4). (Siano et al., 2002).

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

34

•

Vol. 7 n. 2 Giugno 2002

RASSEGNA SCIENTIFICA

Fig. 5. The copper axe of the Iceman (3200 BC, Ötztal, Eastern Alps) with its original handle and bindings.

Fig. 6. Experimental pole figures of a copper axe obtained by neutron diffraction at ILL .Texture analysis provides information on heat and cold treatments during manufacture.

Vol. 7 n. 2 Giugno 2002

•

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

35

RASSEGNA SCIENTIFICA

rosion phases produced by changes in the environment (e.g. patina, black crusts, etc.).

Owing to the non-destructive character of neutron techniques, their applicability to relatively large, intact, and precious archaeological objects is obvious. Additionally, the large interaction volume and rapid data collection achievable at future neutron sources will provide a range of new applications in the study and conservation of historical artefacts. TOF neutron diffraction provides new and unique information to that from x-ray diffraction. No preparation of the objects is needed and the experimental set-up is simple and free of sample movements. Ultimately, restoration and conservation problems relating to artefacts such as that reported in Figure 1 can be very effectively addressed through this wide variety of neutron scattering techniques.

4. Ceramics Correlations between phases or ratios of phase proportions, may be used to characterise or classify an artefact.

During ceramics firing the starting materials undergo solid state reactions with products strongly dependent upon the firing temperature, duration and atmosphere of the process. Ancient or pre-historic ceramics fired at moderate temperatures, often exhibit very complex diffraction patterns due to a wide variety of mineral phases, among them clay minerals and sheet silicates which need high intensity and resolution for identification and quantification. Neutron diffraction allows the use of the whole artefact as sample material without disturbing it or modifying it in any way.

One, fairly straightforward example of neutron diffraction is provided by the patterns obtained from an undisturbed ceramic Greek wine jug shown in Figure 2 (Kockelmann et al., 2000).

Another example of the application of fingerprinting is that of medieval German ceramics from Siegburg and Brühl, two prominent sites for stoneware development and production in the Middle Ages, where the presence of cristobalite is characteristic of Brühl pottery. Characterisation of pottery fragments by mineral phase fractions derived by Rietveld analysis of TOF neutron diffraction is shown in Figure 3 (Kockelmann et al., 2001).

5. Metal artefacts Materials and metals in particular, change their microscopic structure as a result of mechanical or thermal treatments during manufacturing. This implies that a structural analysis by neutron diffraction may give valuable information about ancient production processes.

This has been demonstrated by TOF neutron diffraction analysis in the case of an Etruscan bronze vessel (Figure

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

36

•

Vol. 7 n. 2 Giugno 2002

4). The compositions of the bottom and the wall of the object were determined to be typical for classical bronzes with 90% copper and 10% tin. Interestingly, a significant amount of lead was found in the handle, and a repair patch at the base of the vessel revealed a considerable degree of corrosion as indicated by the detection of a substantial amount of cuprite (copper oxide). Furthermore, from detailed analysis of the diffraction peak profiles it was possible to distinguish the underlying original bronze from the patch material which is almost pure copper.

More information is obtained by Rietveld refinement analysis of the peak profiles and comparison with analogous spectra from modern reference samples produced under controlled conditions. Raw casting of the jug’s handle is indicated by broad and structured bronze peaks, whereas the much narrower peaks of the wall suggest partial recrystallisation by mechanical and thermal treatment. These results are important because the manufacturing techniques of such small vessels are not yet entirely understood.

Neutron diffraction is particularly powerful for the analysis of the interior of materials, such as stackings of metal sheet, coins with coatings, or objects located inside sealed containers. There is further potential of neutron diffraction for investigating the volume textures and grain distributions of metal objects. Texture is a case study of its own and is an important characteristic for mechanically treated archaeological artefacts. The grain distributions in coins for example could be used to discriminate authentic objects from forgeries or fakes, or to distinguish between differently struck coins.

A very recent example concerning the interpretation of metal textures is the analysis of Copper Age axes per-

Fig. 7. Neutron scattering can provide information on microstructure, phase composition and texture, of undisturbed archaeological objects.

The capabilities of next generation neutron sources promise to yield images of inner fabrics, such as those reported in the figure (obtained by SEM and XRD), through the two- but also the three-dimensional reconstruction of signals collected without sampling the object or sample preparation.

RASSEGNA SCIENTIFICA

formed by neutron diffraction. Among others, the unique copper axe found together with the mummified body of the 5200 years old Iceman (Ötztal Mountains, Eastern Alps) was analysed by neutron diffraction techniques at the ILL (Figure 5). This is the only prehistoric axe ever found with the original handle and bindings.

Full, non-destructive texture analysis has proven that textural information can be successfully extracted from the diffraction data irrespective of the shape of the object, and that the specific manufacturing history of each axe can be derived (Figure 6).

6. Forecast of novel opportunities at next generation Neutron Sources Neutron diffraction represents a very promising archaeometric tool and the knowledge of its potential in the examination of artefacts of nearly all shapes and materials in a truly non-destructive manner is still at a very early stage of exploitation by the relevant science community. The examples of neutron studies on artefacts and archaeological objects presented here are all very recent and some of the achievements are still far from the goals envisaged, mainly due to limitations of present neutron sources and instrumentations. The next generation of neutron sources promises to provide all the information on phase composition, inner fabric and texture for undisturbed art objects such as envisaged in Figure 7.

The unique capabilities offered by an ESS-class neutron source as regards intensity and the corresponding advancements in time-of-flight instruments will allow the simultaneous detection of weak and/or very subtle signals and will enable combined analyses of phase identification, phase fraction, microstructure and texture on both, very small and large objects. Referring to the examples given here, the proposed ESS neutron source will allow neutron studies beyond current thresholds in the following areas: - Phase and microstructural characterisation of stones and ceramics by investigating large suites of site-specific objects and, for comparison purposes, also of well-defined reference samples in a reasonable time and finally on a routine basis.

- Combined texture and microstructure analysis of metallic objects, such as the Iceman axe, in order to get complementary information on the manufacturing conditions by analyses of grain size and strain as well as preferred orientation of crystallites, again also on comparative samples obtained by different manufacturing processes.

- Texture analysis of precious and large or heavy objects in a complete stationary experimental set-up which is possible only at TOF-instruments with a wide threedimensional detector arrangement surrounding the object.

This paper draws upon the Report on Cultural Heritage presented at the ESS European Conference in Bonn, Germany 16-17 May, 2002. available on the web site: http://www.esseurope.de References 1. Kardjilov, N., Baechler, S., Lehmann, E., Frei, G. (2002) Applied energy-selective neutron radiography and tomography with cold neutrons. ESS European Conference, Abstract Book, p.137. Web site: http://www.ess-europe.de.

2. Kockelmann, W., Kirfel, A., Hähnel, E. (2001) Non-destructive phase analysis of archaeological ceramics using tof neutron diffraction, J. Archaeological Science, 28, 213-222.

3. Kockelmann, W., Pantos, E., Kirfel, A. (2000) Radiation in Art and Archaeometry Edited by: D.C. Creagh, D.A. Bradley. Elsevier Science B.V., ISBN: 0-444-50487-7, p. 347-377 4. Schäfer, W. (2002). Neutron diffraction applied to geological texture and stress analysis. Eur. J. Mineral. 14/II, 263-290.

5. Siano, S., Kockelmann, W., Bafile, U., Celli, M., Iozzo, M., Miccio, M., Moze, O., Pini, R., Salimbeni, R., Zoppi, M. (2002) Quantitative multiphase analysis of archaeological bronzes by neutron diffraction, Applied Physics A, in print.

6. Winkler, B., Knorr, K., Kahle, A., Vontobel, P., Lehman, E., Hennion, B., Bayon, G. (2002) Neutron imaging and neutron tomography as non-destructive tools to study bulk rock samples. Eur. J. Mineral. 14/II, 349-354.

Vol. 7 n. 2 Giugno 2002

•

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

37

PROGETTO E.S.S.

PRESENTATION OF THE EUROPEAN SPALLATION SOURCE (ESS) PROPOSAL The ESS project proposal was presented at the European Source of Science conference in Bonn, in the former House of Parliament of the Federal Republic of Germany from 15-17 May 2002.

More than 750 scientists from 22 European countries attended the conference and its satellite meetings. The total number of participants was around 900. The conference presents an important milestone for the ESS project.

The proposal and science case is now in place and we have entered the decision phase for the ESS. Provided the decision to build is taken within the year 2003 or early 2004, the ESS may be in operation in the year 2011.

After words of welcome from the Chairman of the ESS Council, P.Tindemans, the Secretary of State of NordRhein Westfalia, H. Krebs, on behalf of the Prime Minister W. Clement, spoke about the advantages and attractiveness - to any region in Europe - of hosting the ESS facility. He underlined this statement effectively by reporting that NRW was prepared to contribute 10% of the full ESS construction budget if NRW was selected to host the ESS facility.

The need for investment in Large scale facilities in general and the ESS in specific was prominently stated in the talks of Prof. E. Banda from the European Science Foundation and Prof. B. Cywinski from the European Neutron Scattering Association.

The two speakers also referred to the OECD recommendation to build a third generation neutron source in each of the three major economic regions: America, Asia and Europe. A recommendation that only Europe lacks to follow. The 30 year European lead in the field of neutron scattering is threatened by the US and Japanese projects that will deliver their first neutrons in 2006 and 2007 and claim World leadership a couple of years later.

The general science case for the ESS, with strong emphasis on the new opportunities ESS will provide in a very broad range of disciplines, was convincingly presented

by D. Richter the chairman of the ESS-SAC. The ESS Technical Project was presented by the ESS-Project Director J.-L. Laclare. Three specific examples of the scientific opportunities with the ESS in three key technological areas were described by three eminent scientists: Ph. Whiters on Engineering, G.Aeppli on Information Technology and O.Byron on Biotechnology.

On May 17, seven scientific talks demonstrated how the huge step in source quality provided by the ESS would allow completely new scientific and technological problems to be addressed in these seven fields of science ranging from fundamental physics to biology, from information technology to engineering and sustainable development. The ESS will be an extremely versatile tool.

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

38

•

Vol. 7 n. 2 Giugno 2002

On May 15, a number of satellite meetings took place.

The German Neutron Society held its 2002 annual meeting in the Wasserwerk, the building used by the German parliament during the re-construction of the Bundeshaus in Bonn; other neutron scattering societies organized similar meetings: the Czech, Slovak, Dutch, Italian, Swiss and the Polish neutron societies all met in Bonn as satellite meetings. The board of the Italian, French and Scandinavian neutron scattering societies also met in Bonn. All the European communities are strongly in favour of the construction of the ESS. The EU supported neutron related instrumentation development networks in particular, ENPI, DLAB, e-VERDI, SCANS, TECHNI and VESUVIO also wanted to express their interests in the ESS, by arranging their annual meetings as a satellite event on May 15 in Bonn. The Neutron Round Table used the opportunity to organise a joint RTD network meeting with all the networks coordinators. Two major European neutron user facilities did want to be present in Bonn and had their annual user meeting as satellite meetings of the ESS European Conference.

The event was followed by 50 journalists from the major European countries and a press conference was organized on May 16, 2002. Moreover, 10 companies from 6 European countries were present in Bonn with their products, demonstrating the industrial competence within Europe to construct the ESS facility.

Five different regions in Europe 1) Yorkshire and 2) Oxfordshire in the UK, 3) Sachsen and Sachsen-Anhalt and 4) Nord-Rhein Westfalia in Germany and 5) a Scandinavian consortium, presented their interest to host the ESS, in very impressive documentations and stands at the conference.

In conclusion, the ESS project has entered a new phase.

The ESS science case is now accepted as strong and well presented, the chosen technical solution has been deemed convincing and within the capability of European industry and the institutions behind the ESS project. The ESS facility will be the premier neutron source in the World – about an order of magnitude better than the US and Japanese projects. In short: The ESS project is ready and timely – we can do it! – the next step is to induce the European governments and the EU to arrive at a decision that will allow us realise the ESS.

F. Carsughi ESS Central Project Team

CALENDARIO

25 giugno - 16 agosto 2002

VARENNA, ITALY

International School of Physics “Enrico Fermi” Courses 2002 http://www.sif.it/sif/sif/varenna/2002-courses.html

15-20 luglio 2002

ERICE, ITALY

Euroconference Quantum Phases at the Nanoscale (Nanophase)

20 luglio - 1 agosto 2002 New Trends Nanoscience)

in

Physics

(Towards

VILLIGEN, SWITZERLAND

Neutron and Synchrotron X-ray Scattering Condensed -Matter Research (NSCMR2002) http://www.psi.ch/sls/NSCmr2002

25-29 agosto 2002

in

VENEZIA, ITALY

XII International Conference on Small Angle Scattering A satellite Conference of the 19th IUCR Congress http://www.infm.it

7-12 settembre 2002

FRASCATI, ITALY

School and Workshop on Nanotubes Nanostructures http://www.lnf.infn.it/conference/nn2002

23 settembre - 3 ottobre 2002

and

PALAU, ITALY

VI Scuola di Spettroscopia Neutronica “Francesco paolo Ricci” (I Neutroni come Sonda Microscopica di Sistemi Disordinati) http://www.sisn.it

ERICE, ITALY

Mesoscopic

4 - 6 agosto 2002

23-28 settembre 2002

12-14 dicembre 2002

GRENOBLE, FRANCE

Workshop on the prospectives in Single Crystal Neutron Spectroscopy (SCNS) http://www.ill.fr/Events/ONSITE/SCNS/index.html e-mail sncs@ill.fr

4-7 agosto 2003

VENEZIA, ITALY

Polarised Neutrons and Synchrotron X-rays for Magnetism.

A satellite of the International Conference of Magnetism, Rome 2003. http://venice.infm.it http://www.icm2003.mlib.cnr.it

SAN FELIU DE G., SPAIN

Euresco Conference - Computational Biophysics: Integrating Theoretical Physics and Biology. From the Electronic to the Mesoscale.

11-14 settembre 2002

TRENTO, ITALY

XVI Congresso Nazionale della Società Italiana di Biofisica Pura e Applicata e I Workshop di Biofisica Italiano-Sloveno http://www.science.unitn.it/SIBPA2002/

15-20 settembre 2002

BRATISLAVA, SLOVAKIA

International Conference on Thin Films http://www.ictf12.savba.sk

Vol. 7 n. 2 Giugno 2002

•

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

39

VARIE

CONSIGLIO NAZIONALE DELLE RICERCHE

ISTITUTO NAZIONALE PER LA FISICA DELLA MATERIA

VI Scuola di Spettroscopia Neutronica ‘‘Francesco Paolo Ricci’’ I neutroni come sonda microscopica di sistemi disordinati Hotel Capo d’Orso - Località Cala Capra, Palau (SS) 23 settembre - 3 ottobre 2002 DOCENTI A. Albinati U. Balucani C. J. Carlile D. Colognesi A. Deriu B. Dorner J. Eckert E. Guarini G. J. Kearley R. Lechner A. Paciaroni M. A. Ricci F. Sacchetti R. Senesi J.-B. Suck G. Zerbi M. Zoppi

Università di Milano IFAC-CNR, Firenze ILL, Grenoble IFAC-CNR, Firenze Università di Parma ILL, Grenoble Los Alamos National Laboratories INFM, Firenze IRI, Technische Universiteit Delft HMI, Berlin Università di Perugia Università di Roma Tre Università di Perugia Università di Roma Tor Vergata Universität Chemnitz Politecnico di Milano IFAC-CNR, Firenze

• La Scuola si articola in lezioni di carattere generale, lezioni applicative ed esercitazioni in piccoli gruppi di studenti sotto la guida di tutors.

• Il numero degli studenti è limitato a 30. Persone con precedente esperienza nel campo potranno essere ammesse come osservatori.

• Il costo di partecipazione di 700 comprende lezioni ed esercitazioni pratiche ed il trattamento di pensione com pleta presso l’Hotel Capo d’Orso (www.delphina.it/orso.htm) per tutta la durata della Scuola. E’ disponibile un certo numero di borse a copertura del costo di partecipazione.

• La domanda di iscrizione, da inoltrare entro il 30 Giugno 2002, deve essere fatta compilando il modulo di partecipazione reperibile all’indirizzo www.sisn.it. L’accettazione delle iscrizioni, e della eventuale assegnazione della borsa, verrà comunicata entro il 31/07/2002.

SCADENZA PER LE ISCRIZIONI 30 Giugno 2002 Direttori: Caterina Petrillo, Dipartimento di Fisica, Politecnico di Milano, e INFM – Ubaldo Bafile, Istituto di Fisica Applicata “Nello Carrara”, CNR, Firenze Segreteria: Grazia Ianni, Istituto di Struttura della Materia, CNR, Sede di Roma Montelibretti, Area della Ricerca di Roma, Via Salaria, km 29,300 - 00016 Monterotondo Scalo (RM) - Tel: 06 90672285, Fax: 06 90672316, e-mail: grazia.ianni@mlib.cnr.it Si ringrazia il Dipartimento di Chimica dell’Università di Sassari per aver contribuito al finanziamento della Scuola

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

40

•

Vol. 7 n. 2 Giugno 2002

VARIE

VI Scuola di Spettroscopia Neutronica ‘‘Francesco Paolo Ricci’’ I neutroni come sonda microscopica di sistemi disordinati Hotel Capo d’Orso - Località Cala Capra, Palau (SS) 23 settembre - 3 ottobre 2002

MODULO DI ISCRIZIONE Nome: ......................................................... Cognome: ...................................................................................................

Posizione attuale (laureando, dottorando, borsista, etc.):................................................................................................. ...........................................................................................................................................................................................

Affiliazione: ..................................................................................................................................................................... ...........................................................................................................................................................................................

Indirizzo: ...........................................................................................................................................................................

Telefono: .............................................................. Fax: ................................................................................................... e-mail: ...............................................................................................................................................................................

Campo di attività:.............................................................................................................................................................. ........................................................................................................................................................................................... ...........................................................................................................................................................................................

Richiede una borsa a copertura del costo di partecipazione (No | Parziale | Totale): ...........................................................................................................................................................................................

Arrivo (nave | aereo): ........................................... Ore: ................................................

Partenza (nave | aereo): ........................................ Ore: ................................................

Il modulo di iscrizione deve essere inviato entro il 30 giugno 2002 alla segreteria della Scuola, preferibilmente per posta elettronica. Qualunque comunicazione agli iscritti sarà effettuata per posta elettronica all’indirizzo indicato nel modulo. Si prega di comunicare eventuali variazioni.

L’arrivo e la registrazione avranno luogo nel pomeriggio di lunedì 23 settembre. La Scuola termina la mattina di giovedì 3 ottobre.

Segreteria:

Sig.ra Grazia Ianni, Istituto di Struttura della Materia, CNR, Sede di Roma Montelibretti Area della Ricerca di Roma, Via Salaria, km 29,300 00016 Monterotondo Scalo (RM) Tel: 06 90672285, Fax: 06 90672316 e-mail: grazia.ianni@mlib.cnr.it

Vol. 7 n. 2 Giugno 2002

•

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

41

SCADENZE

Scadenze per richieste di tempo macchina presso alcuni laboratori di Neutroni

Scadenze per richieste di tempo macchina presso alcuni laboratori di Luce di Sincrotrone

ISIS

ALS

La scadenza per il prossimo call for proposals è il 16 ottobre 2002 e il 16 aprile 2003

Le prossime scadenze sono il 15 marzo 2003 (cristallografia macromolecolare) e il 1 giugno 2003 (fisica)

ILL BESSY

La scadenza per il prossimo call for proposals è il 22 settembre 2002 e il 24 febbraio 2003

Le prossime scadenze sono il 4 agosto 2002 e il 15 febbraio 2003

LLB-ORPHEE-SACLAY La scadenza per il prossimo call for proposals è il 1 ottobre 2002 per informazioni: Secrétariat Scientifique du Laboratoire Léon Brillouin, TMR programme, Attn. Mme C. Abraham, Laboratoire Léon Brillouin, CEA/SACLAY, F-91191 Gif-sur-Yvette, France.

Tel: 33(0)169086038; Fax: 33(0)169088261 e-mail: abraham@bali.saclay.cea.fr http://www-llb.cea.fr

DARESBURY La prossima scadenza è il 31 ottobre 2002 e il 30 aprile 2003

ELETTRA Le prossime scadenze sono il 31 agosto 2002 e il 28 febbraio 2003

ESRF BENSC La scadenza è il 15 settembre 2002 e il 15 marzo 2003

Le prossime scadenze sono il 1 settembre 2002 e il 1 marzo 2003

GILDA

RISØ E NFL

(quota italiana) Le prossime scadenze sono il 1 novembre 2002 e il 1 maggio 2003

La scadenza per il prossimo call for proposals è il 1 aprile 2003

HASYLAB (nuovi progetti) Le prossime scadenze sono il 1 settembre 2002, il 1 dicembre 2002 e il 1 marzo 2003

LURE La prossima scadenza è il 30 ottobre 2002

MAX-LAB La scadenza è approssimativamente febbraio 2003

NSLS Le prossime scadenze sono il 30 settembre 2002, il 31 gennaio 2003 e il 31 maggio 2003

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

42

•

Vol. 7 n. 2 Giugno 2002

FACILITIES

LUCE DI SINCROTRONE SYNCHROTRON SOURCES WWW SERVERS IN THE WORLD (http://www.esrf.fr/navigate/synchrotrons.html)

ALS Advanced Light Source MS46-161, 1 Cyclotron Rd Berkeley, CA 94720, USA tel:+1 510 486 4257 fax:+1 510 486 4873 http://www-als.lbl.gov/ Tipo: D Status: O AmPS Amsterdam Pulse Stretcher NIKEF-K, P.O. Box 41882, 1009 DB Amsterdam, NL tel: +31 20 5925000 fax: +31 20 5922165 Tipo: P Status: C APS Advanced Photon Source Bldg 360, Argonne Nat. Lab. 9700 S. Cass Avenue, Argonne, Il 60439, USA tel:+1 708 252 5089 fax: +1 708 252 3222 http://epics.aps.anl.gov/welcome.html Tipo: D Status: C ASTRID ISA, Univ. of Aarhus, Ny Munkegade, DK-8000 Aarhus, Denmark tel: +45 61 28899 fax: +45 61 20740 Tipo: PD Status: O BESSY Berliner Elektronen-speicherring Gessell.für Synchrotron-strahlung mbH Lentzealle 100, D-1000 Berlin 33, Germany tel: +49 30 820040 fax: +49 30 82004103 http://www.bessy.de Tipo: D Status: O BSRL Beijing Synchrotron Radiation Lab. Inst. of High Energy Physics, 19 Yucuan Rd.PO Box 918, Beijing 100039, PR China tel: +86 1 8213344 fax: +86 1 8213374 http://solar.rtd.utk.edu/~china/ins/IHEP/bsrf/bsrf.html Tipo: PD Status: O

Tipo: PD Status: O DAFNE INFN Laboratori Nazionali di Frascati, P.O. Box 13, I-00044 Frascati (Rome), Italy tel: +39 6 9403 1 fax: +39 6 9403304 http://www.lnf.infn.it/ Tipo:P Status: C DELTA Universität Dortmund,Emil Figge Str 74b, 44221 Dortmund, Germany tel: +49 231 7555383 fax: +49 231 7555398 http://prian.physik.uni-dortmund.de/ Tipo: P Status: C ELETTRA Sincrotrone Trieste, Padriciano 99, 34012 Trieste, Italy tel: +39 40 37581 fax: +39 40 226338 http://www.elettra.trieste.it Tipo: D Status: O ELSA Electron Stretcher and Accelerator Nußalle 12, D-5300 Bonn-1, Germany tel:+49 288 732796 fax: +49 288 737869 http://elsar1.physik.uni-bonn.de/elsahome.html Tipo: PD Status: O ESRF European Synchrotron Radiation Lab. BP 220, F-38043 Grenoble, France tel: +33 476 882000 fax: +33 476 882020 http://www.esrf.fr/ Tipo: D Status: O EUTERPE Cyclotron Lab.,Eindhoven Univ. of Technol, P.O.Box 513, 5600 MB Eindhoven, The Netherlands tel: +31 40 474048 fax: +31 40 438060 Tipo: PD Status: C

CAMD Center Advanced Microstructures & Devices Lousiana State Univ., 3990 W Lakeshore, Baton Rouge, LA 70803, USA tel:+1 504 3888887 fax: +1 504 3888887 http://www.camd/lsu.edu/ Tipo: D Status: O

HASYLAB Notkestrasse 85, D-2000, Hamburg 52, Germany tel: +49 40 89982304 fax: +49 40 89982787 http://www.desy.de/pub/hasylab/hasylab.html Tipo: D Status: O

CHESS Cornell High Energy Synchr. Radiation Source Wilson Lab., Cornell University Ithaca, NY 14853, USA tel: +1 607 255 7163 fax: +1 607 255 9001 http://www.tn.cornell.edu/

INDUS Center for Advanced Technology, Rajendra Nagar, Indore 452012, India tel: +91 731 64626

Vol. 7 n. 2 Giugno 2002

•

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

43

FACILITIES

Tipo: D Status: C KEK Photon Factory Nat. Lab. for High Energy Physics, 1-1, Oho, Tsukuba-shi Ibaraki-ken, 305 Japan tel: +81 298 641171 fax: +81 298 642801 http://www.kek.jp/ Tipo: D Status: O Kurchatov Kurchatov Inst. of Atomic Energy, SR Center, Kurchatov Square, Moscow 123182, Russia tel: +7 95 1964546 Tipo: D Status:O/C LNLS Laboratorio Nacional Luz Sincrotron CP 6192, 13081 Campinas, SP Brazil tel: +55 192 542624 fax: +55 192 360202 Tipo: D Status: C

MAX-Lab Box 118, University of Lund, S-22100 Lund, Sweden tel: +46 46 109697 fax: +46 46 104710 http://www.maxlab.lu.se/ Tipo: D Status: O NSLS National Synchrotron Light Source Bldg. 725, Brookhaven Nat. Lab., Upton, NY 11973, USA tel: +1 516 282 2297 fax: +1 516 282 4745 http://www.nsls.bnl.gov/ Tipo: D Status: O NSRL National Synchrotron Radiation Lab. USTC, Hefei, Anhui 230029, PR China tel:+86 551 3601989 fax:+86 551 5561078 Tipo: D Status: O Pohang Pohang Inst. for Science & Technol., P.O. Box 125 Pohang, Korea 790600 tel: +82 562 792696 f +82 562 794499 Tipo: D Status: C Siberian SR Center Lavrentyev Ave 11, 630090 Novosibirsk, Russia tel: +7 383 2 356031 fax: +7 383 2 352163 Tipo: D Status: O

SSRL Stanford SR Laboratory MS 69, PO Box 4349 Stanford, CA 94309-0210, USA tel: +1 415 926 4000 fax: +1 415 926 4100 http://www-ssrl.slac.stanford.edu/welcome.html Tipo: D Status: O SRS Daresbury SR Source SERC, Daresbury Lab, Warrington WA4 4AD, U.K. tel: +44 925 603000 fax: +44 925 603174 E-mail: srs-ulo@dl.ac.uk http://www.dl.ac.uk/home.html Tipo: D Status: O SURF B119, NIST, Gaithersburg, MD 20859, USA tel: +1 301 9753726 fax: +1 301 8697628 http://physics.nist.gov/MajResFac/surf/surf.html Tipo: D Status: O TERAS ElectroTechnical Lab. 1-1-4 Umezono, Tsukuba Ibaraki 305, Japan tel: 81 298 54 5541 fax: 81 298 55 6608 Tipo: D Status: O UVSOR Inst. for Molecular ScienceMyodaiji, Okazaki 444, Japan tel: +81 564 526101 fax: +81 564 547079 Tipo: D Status: O D = macchina dedicata; PD = parzialmente dedicata; P = in parassitaggio.

O= macchina funzionante; C=macchina in costruzione.

D = dedicated machine; PD = partially dedicated; P = parassitic.

SPring-8

44

SRC Synchrotron Rad. Center Univ.of Wisconsin at Madison, 3731 Schneider DriveStoughton, WI 53589-3097 USA tel: +1 608 8737722 fax: +1 608 8737192 http://www.src.wisc.edu Tipo: D Status: O SRRC SR Research Center 1, R&D Road VI, Hsinchu Science, Industrial Parc, Hsinchu 30077 Taiwan, Republic of China tel: +886 35 780281 fax: +886 35 781881 http://www.srrc.gov.tw/ Tipo: D Status: O

LURE Bât 209-D, 91405 Orsay ,France tel: +33 1 64468014; fax: +33 1 64464148 E-mail: lemonze@lure.u-psud.fr http://www.lure.u-psud.fr Tipo: D Status: O

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

2-28-8 Hon-komagome, Bunkyo-ku ,Tokyo 113, Japan tel: +81 03 9411140 fax: +81 03 9413169 Tipo: D Status: C SOR-RING Inst. Solid State Physics S.R. Lab, Univ. of Tokyo, 3-2-1 Midori-cho Tanashi-shi, Tokyo 188, Japan tel: +81 424614131 ext 346 fax: +81 424615401 Tipo: D Status: O

O= operating machine; C= machine under construction.

•

Vol. 7 n. 2 Giugno 2002

FACILITIES

NEUTRONI NEUTRON SCATTERING WWW SERVERS IN THE WORLD (http://www.isis.rl.ac.uk)

Atominstitut Vienna (A) Facility: TRIGA MARK II Type: Reactor. Thermal power 250 kW. Flux: 1.0 x 1013 n/cm2/s (Thermal); 1.7 x 1013 n/cm2/s (Fast) Type of instruments available to external users: SANS, Interferometer, Depolarisation, Transmission Expts, neutron radiography.

Address for information: Atominstitut Oesterreichischen Universitaeten Stadionallee 2 A-1020 Wien Prof. H. Rauch Tel: +43 1 58801 14168; Fax: +43 1 58801 141199 E-mail: boeck@ati.ac.at http://www.ati.ac.at

BNL (USA) Brookhaven National Laboratory, Biology Department, Upton, NY 11973, USA Dieter Schneider; General Information: Rae Greenberg; Tel: +1 516 282 5564 Fax: +1 516 282 5888 http://neutron.chm.bnl.gov/HFBR/

Budapest Neutron Centre BRR (H) Type: Reactor. Flux: 2.0 x 1014 n/cm2/s Number of instruments available to external users: 9 Type of instruments available to external users: 1 powder/liquid diffractometer; 1 single crystal diffractometer*; 1 SANS; 1 reflectometer*; 2 3-axis spectrometers; 2 Neutron gamma activation analysis * Under construction.

Dates for proposal submission: June 15/November 15 Date for selection process: July/December Related scheduling periods: August-December/JanuaryJune.

Address for application forms: Dr. Borbely Sándor, KFKI Building 10, 1525 Budapest, Pf 49, Hungary E-mail: Borbely@power.szfki.kfki.hu http://www.iki.kfki.hu/nuclear

FRJ-2 Forschungszentrum Jülich (D) Type: Dido reactor. Flux: 2 x 1014 n/cm2/s Number of instruments available to external users: 15 Type of instruments available to external users: 2 powder/liquid diffractometers; 2 single crystal diffractometers; 2 SANS; 1 duble crystal diffractometer; 3 3-axis spectrometers; 1 quasielastic diffractometer; 1 TOF (MET); 2 backscattering spectrometers; 1 β-NMR Dates for proposal submission: no formal selection process.

Informal proposals to: Prof. D. Richter, Forschungszentrums Jülich GmbH, Institut für Festkörperforschung, Postfach 19 13, 52425 Jülich, Germany Tel: +49 2461161 2499; Fax: +49 2461161 2610 E-mail: d.richter@kfa-juelich.de http://www.kfa-juelich.de

FRG-1 Geesthacht (D) Type: Swimming Pool Cold Neutron Source. Flux: 8.7 x 1013 n/cm2/s Number of instruments available to external users: 10 Type of instruments available to external users: 1 four circle texture diffractometer; 2 residual stress diffractometers; 2 SANS; 2 reflectometers; 1 TOF spectrometer for basic research; 2 duble crystal diffractometer for high resolution SANS; 1 3-dimens. polarisation analysis diffractometer.

Polarised neutrons available on 5 instruments Dates for proposal submission: any time Dates for selection process: within 4 weeks of submission Address for application forms and informations: Reinhard Kampmann, Institute for Materials Science, Div. Wfn-Neutronscattering, GKSS, Research Centre, 21502 Geesthacht, Germany Tel: +49 (0)4152 87 1316/2503; Fax: +49 (0)4152 87 1338 E-mail: reinhard.kampmann@gkss.de http://www.gkss.de

Vol. 7 n. 2 Giugno 2002

•

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

45

FACILITIES

HMI Berlin BER-II (D) Facility: BER II, BENSC Type: Swimming Pool Reactor. Flux: 2 x 1014 n/cm2/s Number of instruments available to external users: >17 Type of instruments available to external users: 2 powder/liquid diffractometers; 3 3-axis spectrometers; 4 single crystal diffractometers; 1 quasielastic spectrometer; 1 membrane diffraction; 2 TOF (MET); 2 SANS; 1 spin echo; 1 reflectometer; 1 neutron interferometer; 1 β-NMR; 1 cold source.

NB: for many instruments options include polarisation, high fields, high pressures and low temperatures.

Dates for proposal submission: 15 March/15 September Dates for selection process: May/November Related scheduling periods: July-December/January-June Address for application forms: Dr. Rainer Michaelsen, BENSC, Scientific Secretary, Hahn-Meitner-Insitut, Glienicker Str 100, 14109 Berlin, Germany Tel: +49 30 8062 2304/3043; Fax: +49 30 8062 2523/2181 E-mail: michaelsen@hmi.de http://www.hmi.de/

IBR2 Dubna (RU) Type: Pulsed Reactor. Flux: 3 x 1016 (thermal n in core) Number of instruments available to external users: 12 Type of instruments available to external users: 4 powder/liquid diffractometers; 1 single crystal diffractometer; 1 SANS; 2 reflectometers; 1 quasielastic spectrometer; 2 TOF (MET); 1 spin echo.

Dates for proposal submission: 16 October/16 May Dates for selection process: 30 January/15 September Related scheduling periods: February-June/OctoberFebruary Address for application forms: Dr. Vadim Sikolenko, Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, 141980 Dubna, Moscow Region, Russia.

Tel: +7 09621 65096; Fax: +7 09621 65882 E-mail: sikolen@nf.jinr.dubna.su http://nfdfn.jinr.dubna.su/

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

46

•

Vol. 7 n. 2 Giugno 2002

ILL Grenoble (F) Type: 58MW High Flux Reactor. Flux: 1.5 x 1015 n/cm2/s Number of instruments available to external users: 36 Type of instruments available to external users: 5 powder/liquid diffractometers; 7 single crystal diffractometers; 2 SANS*; 3 reflectometers*; 5 polarised neutron instruments*; 2 Nuclear Physics; 6 3-axis spectrometers; 2 backscattering spectrometers; 3 TOF (MET); 2 spin echo; 2 Fudamental Physics. * Some double counting NB: 7 of the above instruments are operated and supported by Collaborative Research Groups (CRGs) Dates for proposal submission: 15 February/31 August Dates for selection process: April/October Related scheduling periods: July-Decem./January-June Address for application forms: Dr. H. Büttner, Scientific Coordination Office, ILL, BP 156, 38042 Grenoble Cedex 9, France Tel: +33 4 7620 7179; Fax: +33 4 76483906 E-mail: buttner@ill.fr http://www.ill.fr IPNS (USA) Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439-4814, USA P.Thiyagarajan,Bldg.200,RM. D125; tel :+1 708 9723593 E-mail: THIYAGA@ANLPNS Ernest Epperson, Bldg. 212; tel: +1 708 972 5701 fax: +1 708 972 4163 or + 1 708 972 4470 (Chemistry Div.) http://pnsjph.pns.anl.gov/ipns.html IRI Delft (NL) Type: 2MW light water swimming pool. Flux: 1.5 x 1013 n/cm2/s Number of instruments available to external users: 5+2* Type of instruments available to external users: 2 powder/liquid diffractometers*; 1 reflectometer; 1 small angle scattering spectrometer*; 1 TOF (MET); 2 polarised neutron instruments. *Instruments located at ECN Petten Dates for proposal submission: no formal selection process Address for application forms: Dr. A.A. van Well, Interfacultair Reactor Institut, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands Tel: +31 15 2784738; Fax: +31 15 2786422 E-mail: vanWell@iri.tudelft.nl http://www.iri.tudelft.nl

FACILITIES

ISIS Didcot (UK) Type: Pulsed Spallation Source. Flux: 2.5 x 1016 n fast/s ISIS operates at 200 µA in 0.4 µs pulsed at 50 Hz Number of instruments available to external users: 24 Type of instruments available to external users: 3.5 powder diffractometers; 1 single crystal diffractometer; 1 SANS; 2 reflectometers; 1 cold neutron test VESTA; 1 single crystal alignment ALF; 5 muon instruments; 1 neutrino facility; 1 3-axis spectrometers; 1.5 quasielastic spectrometer; 4 TOF spectrometers; 1 eV spectrometer; 1 strain/pressure diffractometer.

Dates for proposal submission: 16 April/16 October Dates for selection process: first week of June and Dec. Related scheduling periods: Sept-January/April-August Address for application forms: ISIS Users Liaison Office, Building R3, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX Tel: +44 (0) 1235 445592; Fax: +44 (0) 1235 445103 E-mail: uls@isis.rl.ac.uk http://www.isis.rl.ac.uk JAERI (J) Japan Atomic Energy Research Institute, Tokai-mura, Naka-gun, Ibaraki-ken 319-11, Japan.

Jun-ichi Suzuki (JAERI); Yuji Ito (ISSP, Univ. of Tokyo); fax: +81 292 82 59227 telex: JAERIJ24596 http:// neutron-www.kekjpl

JEEP-II Kjeller (N) Type: D2O moderated 3.5% enriched UO2 fuel. Flux: 2 x 1013 n/cm2/s Number of instruments available to external users: 5 Type of instruments available to external users: 2 powder/liquid diffractometers; 1 single crystal diffractometer*; 1 SANS; 1 3-axis spectrometer*; 1 quasielastic spectrometer (TOF). *The 3-axis instrument may be used as a single crystal diffractometer Dates for proposal submission: no special dates Dates for selection process: no special dates Address for application forms: Institutt for Energiteknikk K.H. Bendiksen, Managing Director, Box 40, 2007 Kjeller, Norway Tel: +47 63 806000, 806275; Fax: +47 63 816356 E-mail: kjell.bendiksen@ife.no http://www.ife.no

LLB Orphée Saclay (F) Type: Reactor. Flux: 3.0 x 1014 n/cm2/s Number of instruments available to external users: 24 Type of instruments available to external users: 6 powder/liquid diffractometers; 2 single crystal diffractometers; 1 Strain diffractometer; 1 Texture diffractometer; 3 SANS; 3 reflectometers; 5 3-axis spectrometers; 1 TOF (MET); 1 spin echo; 1 polarised neutron instrument.

Dates for proposal submission: September Dates for selection process: November Related scheduling periods: January-December Address for application forms: Mrs Claude Rousse, Laboratoire Léon Brillouin, CEASaclay, 91191Gif-sur-Yvette Cedex, France Tel: +33 1 6908 5241/5417; Fax: +33 1 6908 8261 E-mail: rousse@bali.saclay.cea.fr http://www-drn.cea.fr

NFL Studsvik (S) Type: 50 MW reactor. Flux: > 1014 n/cm2/s Number of instruments available to external users: 5 Type of instruments available to external users: 1 powder diffractometer; 1 liquid diffractometer; 1 single crystal diffractometer; 1 residual stress diffractometer; 1 TOF (MET).

Dates for proposal submission: 1 December, 1 April, 1 August (for LSF programme only) Dates for selection process: Decisions before 1 January, 1 May, 1 September (LSF only) Related scheduling periods: January-April/MayAugust/September-December.

Address for application forms: Dr. R. McGreevy, NFL Studsvik, S-611 82 Nyköping, Sweden Tel: +46 155 221000; Fax: +46 155 263070/263001 E-mail: kklingfeldt@studsvik.se http://www.studsvik.uu.se

NIST National Institute of Standards and TechnologyGaithersburg, Maryland 20899 USA C.J. Glinka; tel: + 301 975 6242 fax: +1 301 921 9847 E-mail: Bitnet: GLINKA@NBSENTH Internet: GLIMKA@ENH.NIST.GOV http://rrdjazz.nist.gov

Vol. 7 n. 2 Giugno 2002

•

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

47

FACILITIES

NPI Rez (CZ) Type: 10 MW research reactor.

Address for informations: Zdenek Kriz, Scientif Secretary, Nuclear Research Institute Rez plc, 250 68 Rez, Czech Republic Tel: +420 2 20941177 / 66173428; Fax: +420 2 20941155 E-mail: krz@ujv.cz / brv@nri.cz http://www.nri.cz

ORNL (USA) Oak Ridge National Laboratory Neutron Scattering Facilities, P.O. Box 2008, Oak Ridge TN 37831-6393 USA George D. Wignall, Small Angle Scattering Group Leader Tel: +1 423 574 5237; Fax: +1 423 574 6268 E-mail: wignallgd@ornl.gov http://neutrons.ornl.gov

PSI-SINQ Villigen (CH) Type: Steady spallation source. Flux: 2.0 x 1014 n/cm2/s Number of instruments available to external users: 10 Type of instruments available to external users: 2 powder diffractometers; 1 single crystal diffractometer; 1 SANS; 1 reflectometer; 2 3-axis spectrometers (one for polarised neutrons); 1 TOF (cold neutrons); radiography; prompt gamma analysis.

Related scheduling periods: January-June/JulyDecember.

Address for application forms: Prof. Albert Furrer, Secretariat, Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institute, CH5232 Villigen PSI, Switzerland Tel: +41 56 3102088; Fax: +41 56 3102939 E-mail: albert.furrer@psi.ch http://lns.web.psi.ch

NOTIZIARIO NEUTRONI E LUCE DI SINCROTRONE

48

â&#x20AC;˘

Vol. 7 n. 2 Giugno 2002

TU Munich FRM, FRM-2 (D) Type: Compact 20 MW reactor. Flux: 8 x 1014 n/cm2/s Number of instruments available to external users: 14 Type of instruments available to external users: 1 powder diffractometer; 1 soft phase boundary diffractometer; 2 single crystal diffractometers; 2 single crystal spectrometers; 1 small angle spectrometer/ diffractometer; 2 spin echo spectrometers; 2 3-axis spectrometers; 1 radiography-tomography; 2 TOF spectrometers.

Address for informations: Prof. Winfried Petry, FRM-II Lichtenbergstrasse 1, 85747 Garching Tel: 089 289 14701; Fax: 089 289 14666 E-mail: wpetry@frm2.tum.de http://www.frm2.tu-muenchen.de