A measuring system for time of flight spectrum of neutron based on pulse time sequences detection

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Applied Physics Frontier August 2013, Volume 1, Issue 3, PP.27-31

A Measuring System for Time of Flight Spectrum of Neutron Based on Pulse Time Sequences Detection Yong Ren 1†, Peng Feng 2, Fan Yang 2, Jiansheng Li 3, Deling Mi 2 1. College of Communication Engineering, Chongqing University, Chongqing 400044, China 2. Key Laboratory of Optoelectronics Technology and System, Ministry of Education, Chongqing University, Chongqing 400044, China 3. China Academy of Engineering Physics, P.O. Box 919-210, Mianyang 621900, China †Email:

renyong@cqu.edu.cn

Abstract To measure the time of flight (TOF) spectrum for the

252

Cf fission neutron, a TOF measuring system based on the detected time

sequences of neutron pulse has been proposed and set up. A 252Cf fast ionization chamber combined with traditional electronic circuit is applied in the system to form the neutron flight pulse signals. It can not only detect the pulse sequence on-line with 1 nanosecond precision, but also realize time-digital-convertion simultaneously. The cross correlation function is to calculate the measured spectrum and the numerical statistics of the flight time of neutron and  photons are sent to PC and obtained through data processing. Meanwhile, the timing precision of the system can be judged by the -shape. The distinguishing neutron vs. -photons (n-) can also be achieved by setting a delaying factor. Experimental results show that the proposed system can accurately obtain the TOF spectrum whose precision is better than that of the traditional measuring system. Keywords: 252Cf Source Neutron; TOF Spectrum; Nanosecond Precision; Pulse Sequences Detecting; Correlation Function

1 Introduction As an effective measuring method for fast neutron energy spectrum, Neutron Time of Flight Spectrum (NTFS) measurement is to obtain the flight time distribution of neutrons. Traditional NTFS measuring methods of the 252Cf spontaneous fission neutrons (accompany with γ photons)[1] applying time to amplitude converter(TAC) and multichannel pulse analyzer[2-3] have disadvantages including fixed trigger-time, statistical approximation, absence of original data, combined with -photons interfering, hindering the improvement of time-precision for such kind of method. A new approach to measure NTFS more precisely has been proposed, which is originated from 252Cf source driven power spectral density analysis method[4-5], and utilizes pulse time sequence detecting and correlation function to obtain nanosecond-level TOF. The outline of this paper is as follows: In Section 2, the construction of NTFS measuring system is briefly depicted. Section 3 concretely describes how to detect pulse time signal and process the acquired time sequence with correlation function. Section 4 illustrates the method of discriminating neutron and  photons. Experimental results and performance analysis are presented and discussed in Section 5. Section 6 concludes this paper.

2 Constructions of NTFS Measuring System Fig. 1 is the schematic diagram of the proposed NTFS measuring system. It is consisted of a 252Cf fast ionization chamber, a charge-sensitive-preamplifier, a fast amplifier, two constant ratio timer I and II, a liquid scintillator (BC501), a photomultiplier tube(PMT), a high speed data acquisition card (DAQ, pulse time sequence detector) and a PC. - 27 http://www.ivypub.org/apf/


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