CLASSIFICATION OF WORKING AREAS
Working areas may be classified according to ☼ clean, ☼ supervised, and ☼ controlled area. Classification of areas take into account: ☼ The likelihood & magnitude of potential exposures (risk); and ☼ The nature and extent (keluasan) of the required protection and safety procedure. 3 classes of working areas must be clearly demarcated (disempadankan) and necessary arrangements made to maintain the requirements of the areas classified.
CLEAN AREA The purpose of a Clean Area is to serve as a location within a radioisotope laboratory at which food and beverages may be safely consumed (digunakan) during periods in which radioisotopes are not actively being handled. Work area where the annual dose received by a worker is not likely exceed the dose limit for a member of the public. Clean Areas must be distanced from laboratory areas in which unsealed radioisotopes and other hazardous materials are handled, particularly well away from fume hoods. A person working in a Clean Area must not exceed an effective dose of 1 mSv in any consecutive (berturut-turut) 12-month period.
SUPERVISED AREA
• Work area for which the occupational exposure conditions are kept under review. • Specific protective measures and safety provisions are not normally needed. • Area is clearly demarcated with radiation warning signs and legible (dapat dibaca) notices clearly posted.
• Periodically review the conditions to determine any need for protective measures and safety provisions. • Under normal working conditions a person could receive an effective dose exceeding 1 mSv in any consecutive (berturut-turut) 12-month period.
CONTROLLED AREA
• Specific protection measures and safety provisions are or could be required for:– controlling normal exposures or preventing the spread of contamination (pencemaran) during normal working condition, – preventing (mengelak) or limiting the extent of potential exposures. • Annual dose received by a worker in this area is likely to exceed 3/10 Annual Dose Limit (6 mSv).
• Radiation warning signs and appropriate instructions should be displayed at:– access point; and – other appropriate location within controlled area.
• The controlled area should be provided with:– Protective clothing & equipment – Monitoring equipment for contamination – Suitable storage for personal clothing – Washing or showering facilities – Suitable storage for contaminated protective clothing and equipment – Periodically review conditions of the controlled area
• No person shall enter a controlled area unless he has been assigned to the area or has been authorized to enter the area. • The dose might be due to external radiation or internal contamination or a combination of both. • Under normal working conditions a person could receive an effective dose exceeding 6 mSv in any consecutive (berturut-turut) 12-month period.
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PERSONNEL MONITORING
• Individual dose monitoring shall be undertaken for workers who are normally exposed to radiation in controlled areas: – radiologists, medical physicists, the RPO, radiographers and nurses. – Other frequent users of X Ray systems such as endoscopists, anaesthetists, cardiologists, surgeons etc., as well as ancillary (sampingan) workers who frequently work in controlled areas, shall also be monitored. • Occupational exposure received by working personnel can be delivered by sources outside the body, in the form of external radiation, or radioactive materials deposited in the body as a result of intake of radioactive contaminants while working with the materials.
Dose can be delivered by external or internal sources
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External
Internal
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• For the purpose of personnel monitoring, the BSS regulations require the radiation dose from external radiation and internal contamination to be added up to represent an individual dose in a year. • There are special devices worn by personnel or used to measure the radiation dose received while working with radiation sources or working in classified areas.
• Individual external doses should be determined by using individual monitoring devices: – Thermoluminescent – Film badges – Electronic dosimeters • Worn at breast level, between the shoulders and the waist. • The monitoring period should be one month, and shall not exceed three months. • The exchange of dosimeters and report receipt should not exceed three months.
Several personal dosimeters are recommended
From: Avoidance of radiation injuries from interventional procedures. ICRP draft 2000
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Different types of personal dosimeters…
Film Termoluminescence dosimeters (TLD) Electronic dosimeters
FILM BADGE • Film consists of photographic emulsions mounted in plastic then wrapped (dibalut) in thin, light-tight paper, sandwich fashion and placed in plastic holder called cassette. • Contains cutaway portions to allow the entrance of beta particles.
• Contains various filters – usually copper, cadmium, aluminium and lead – placed in different portion of the cassette to help distinguish (membezakan) photons of different energies. • Able to be clipped on workers’ clothing allowing the measure of whole body exposure and also the ability (keupayaan) to distinguish the types, energy and direction of radiation.
• Advantages of film badge: Inexpensive. It provides a permanent record (film can be reread). Required no technical knowledge of the user. It is able to distinguish between different energies of photons It can measure doses due to different types of radiation. It is quite accurate for exposures greater than 100 millirem.
• Disadvantages of film badge: it must be developed and read by a processor (which is time consuming) prolonged heat exposure can affect the film; hence the badge should not be exposed to sunlight or stored in a warm place such as an automobile (because of the greenhouse effect) exposures of less than 20 millirem of gamma radiation cannot be accurately measured.
Open window Dural Cadmium / lead Tin / lead Lead edge shielding
Open window Plastics Indium
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Open window
-Allows all incident radiation that can penetrate the film wrapping to interact with the film. - Allows for the film serial number to be displayed.
Thin plastic filter Attenuates beta radiation but passes all other radiations. Thick plastic filter
Passes all but the lowest energy photon radiation and absorbs all but the highest energy beta radiation.
Dural filter
Progressively absorbs photon radiation at energies below 65 keV as well as beta radiation.
Tin/lead filter
Allows energy independent dose response of the film over the photon energy range 75 keV to 2MeV.
Cadmium/ lead filter
-The capture of neutrons by cadmium produces gamma rays which blacken the film - Thus enabling assessment of exposure to neutrons.
A strip of indium Becomes radioactive after exposure to neutrons and foil
can be used to identify exposed personnel in the event of a criticality accident.
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THERMOLUMINESCENT DOSIMETERS (TLD) • Substances that possess the property of thermoluminescence are non-metallic crystalline solids. • Electrons in a crystal exist in distinct energy levels, called bands, just as electrons in an atom exist in distinct energy levels, called orbits. • When electrons in a crystal absorb energy, they move to higher energy band.
• In TLD crystal, these excited electrons get trapped in a higher energy state, radiating their extra energy in the form of visible light photons. • The amount of light obtained is proportional to the energy absorbed by the crystal. • Thermoluminescent dosimeter (TLD) rings measure radiation exposure to your extremities due to x-ray, beta, and gamma radiation with an encased lithium fluoride chip. • The TLD chip is sealed beneath the identification cover of the ring.
Ring TLD
Wallet Card Wrist / Ankle TLD
TLD Badge 35
whole body
extremity 36
• Advantages of TLD:☼ Can be reused. ☼ Require no technical knowledge of use. ☼ Can be used several weeks at a time without appreciable loss of stored energy ☼ Can be made tissue-equivalent. ☼ Not as sensitive to moderate heat as is film. ☼ Have an increased sensitivity to a wide photon energy range.
• Disadvantages of TLD:☼ Expensive. ☼ Non-permanent record. ☼ The crystal or powder can give erroneous if damaged or become dirty through careless handling
HANDLING YOUR DOSIMETER (Film badge) • Film used for personnel monitoring is extremely sensitive and must be stored and handled with care. • Film will become permanently (dengan kekal) damaged if subjected to excessive (lebihan) heat, humidity, mechanical pressure or damage. • Exposure to chemical hazards such as ammonia, hydrogen sulphide, or hydrogen peroxide will interfere with accurate interpretation of processed film. • Film packets should be stored in a cool, dry area away from all sources of radiation and chemically active gases or vapours.
• Always wear your own personnel monitor. Never allow another person to wear your badge and never wear a badge assigned to another individual. • Wear the dosimeter between the shoulders and waist with the name facing out. • If you leave your dosimeter at work, keep it in a safe place (e.g., your desk) or where the control is located. • Do not store or leave your dosimeter near sources of ionizing radiation.
• Do not wash your dosimeter because water and heat from a washer/dryer may destroy it or alter (mengubah) the reading. • Do not lose your dosimeter. In the event that it is lost, damaged, or film is missing from the holder, notify your supervisor to arrange for replacement. No work with radiation should take place until the personnel monitor is replaced. • Remember that these devices will not provide any warning when an individual receives a radiation dose. They do not change color, beep, or in any other way visually indicate exposure has been received. Their only function is to legally document the radiation dose an individual may receive from working with radioactive material.
• Never wear your badge when undergoing any type of medical or dental radiographic procedures as a patient. Badges are intended (bertujuan) to measure doses received while performing (menjalankan) your job duties. • If you must take it with you when you travel to other facilities, protect it, particularly from airport x-ray machines. Metal detectors DO NOT damage dosimeters. Note: Some airports used x-ray to check luggage.
POCKET DOSIMETER • A small ionization detection instrument that indicates (menunjukkan) ionizing radiation exposure directly. • Precision instruments about the size of a pocket fountain pen, which are used to measure accumulative doses or quantities of gamma & X-ray radiation. • A metal clip is used to attach the dosimeter to an individual's pocket or to any available object in an area to be monitored for total radiation exposure.
• It is pocket-size, conductive-fibre electroscope with an ion chamber for detecting and indication integrated (gabungan) exposure to gamma and xradiation. • It has a thin wall which permits the penetration and detection of radiation.
Reading a pocket dosimeter… • Point it at a light source so that we can look through it and see the scale. • The conductive fiber moves across a very clear well marked scale that produces the reading.
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Wearing a pocket dosimeter… • Wear the dosimeter like a pen in your pocket, or clip it to your belt. • You can also set it outside for an hour, this will tell you the radiation rate. • You don't have to have a radiation meter if you have a dosimeter and are not in a hurry to measure the rate.
• If ten or a hundred people are together or going somewhere, only one or two of them need to wear a dosimeter. • So long as they all stay together, the radiation dosage that one gets will be what they all get. • The dosimeter is charged (reset to zero) so the dosimeter can be used over and over again. This is usually done before each use. (http://www.arrowtechinc.com/Instructions_Jordan_Charger.htm)
RECORD KEEPING •
Employers & licensees shall maintain and preserve exposure records for each worker.
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Employers & licensees must:- Provide the workers with access to information in their own exposure records. - Give due care and attention to the appropriate confidentiality of records. - Facilitate the provision of copies of workers’ exposure records to new employers when workers change employment
• The exposure records should include:a) Unique identification of the individual b) Information on the general nature of the work involving occupational exposure c) The exposure for the year to date and, when necessary, for the appropriate 5 years period. d) Measurements of external dose e) Measurements of internal dose f) Evaluations of anomalous dose results, such as unexpectedly high or low doses g) Allocated dose for lost or damaged dosimeters or samples h) When a worker is or has been occupationally exposed while in the employment of more than one employer
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Information on the dates of employment with each employer and the doses j) Exposures and intakes in each employment k) Records of any doses due to emergency interventions or accidents, which should be distinguished from doses during normal work l) Records of formal declarations of pregnancy and matters pertaining such condition. m) Lifetime dose to date
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Retention period of record: - Until the worker is or would be 75 years of age, and - 30 years after cessation of work involving occupational exposure.
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The importance of record retention:a) To provide data for analysis of dose distributions b) To evaluate exposure trends which may take into account collective dose c) To optimize the effectiveness of monitoring procedures and programmes d) To provide data for epidemiological studies e) For litigation purposes f) For workers’ compensation cases, which may arise years after the actual or claimed exposure