Radiation Protection Training at BARC-TIFR Pelletron Linac Facility (PLF) PDF

RADIATION PROTECTION TRAINING AT BARC-TIFR PELLETRON LINAC FACILITY (PLF) Health Physics Unit (TIFR), ARSS, HPD, BARC TIFR, Colaba, Mumbai 400005. Radiation Safety – Your Responsibility Radiation safety and protection during every operation involving/generating ionizing radiation...

RADIATION PROTECTION TRAINING AT BARC-TIFR PELLETRON LINAC FACILITY (PLF) Health Physics Unit (TIFR), ARSS, HPD, BARC TIFR, Colaba, Mumbai 400005. Radiation Safety – Your Responsibility Radiation safety and protection during every operation involving/generating ionizing radiation is given top priority in this Facility. However no system can be effective without the co-operation and strict compliance of the guidelines by the persons working in the system. For this reason the radiation worker must be familiar with the hazards involved in the operations and must have skill and conscientiousness in the use of dosimetry & protective devices. It is the responsibility of the staff/students/users to follow the safety rules as a part of their normal duty.  What is Radioactivity ? Substances made up of unstable atom are said to be radioactive. They become stable only by emitting radiations. Emission of ionising energy or ionising energetic particles from radioactive substances/ radiation generating equipment is called “Ionising Radiation”. Types of Ionising Radiation encountered at PLF: Alpha Beta Gamma / X-rays Neutron Charged particle beams Penetrating power  Properties of different radiation Radiation Type of Radiation Mass (AMU) Charge Shielding material Alpha Particle 4 +2 Paper, clothes Plastic, glass, light Beta Particle 1/1836 ±1 metals Dense metal, concrete, Gamma Electromagnetic Wave 0 0 Earth Water,oil, Neutrons Particle 1 0 concrete, polyethylene,  Unit of Radioactivity CURIE (Ci) One curie is that quantity of any radioactive material which is undergoing 3.7 X 1010 disintegration per second (dps). 1 mCi = 3.7 X 107 dps 1mCi = 3.7 X 104 dps BECQUEREL (Bq) It is the SI unit of radioactivity. One Becquerel corresponds to one disintegration per second. 1 Curie (Ci) = 3.7 X 1010 Bq.  Radioactive Half Life Radioactive materials have an associated half-life, or decay time characteristic of that isotope. The amount of time necessary for half of the total amount of radioactive material to decay is called the Half-Life of that material. The radiation dose rate will be decreased by a factor of 2 for every half-life decay Radioactive Decay  Radioactivity symbol Radioactivity symbol or the legend, RADIOACTIVE, written on the label are used to indicate the nature of consignment. Radioactivity symbol is also called a tri-foil symbol. It is the international symbol for radiation. The symbol can be magenta or black, on a yellow background. This sign is pasted where radioactive materials are handled and is used as a warning to indicate presence of radioactivity.  Radiation units Radiation Exposure: The unit of exposure is Roentgen (R) and can only be used for X or gamma radiation in air. 1 R  2.58 x 10 - 4 C/kg Radiation Absorbed Dose: The absorbed dose is the energy deposition per unit mass of the medium by any type of radiation. The unit of absorbed dose is Gray (Gy). [ 100 rad = 1 Gy ] 1 Gy = 1 J/kg Effective Dose: Effective dose is calculated by multiplying the absorbed dose by some weighting factors to take into account radiation effects of different types of radiation on different tissues. The unit of effective dose is Sievert (Sv). [ 100 rem = 1 Sv ]  How Are we affected by radiation “When radiation passes through the body, it breaks some of the molecules in the cells of the body in its path”. The most important target for radiation in the cell is DNA in the nucleus. If the exposure is small or if it is spread over a long period of time, the body’s natural mechanism will repair the damage. Chronic Exposure If the exposure is very high and occurs in a short time, the repair mechanism of the body will not work effectively and you can see the effect of radiations on the body within a short time. Acute Exposure The functions of the organs are impaired only if too many cells are damaged or killed. Extensive damage to DNA can lead to cell death. Large number of cells dying can lead to organ failure and in extreme cases death for the individual. Damaged or improperly repaired DNA may lead to cancer.  Effects of Acute Exposure 0 - 0.25 Sv :There is no observable effect 0.25 - 1 Sv :Slight change in blood 1 – 2 Sv :Vomiting in 50% cases within 3 hrs, with fatigue & loss of appetite. Recovery will be in all cases within a few hours. 2 - 6 Sv :Vomiting in 2 Hours or less, severe blood changes, bleeding and infection, loss of hair after 2 weeks. 20 to 100 % cases recover in1 month to 1 year time. 6 - 10 Sv :Vomiting in 1 hour, severe blood changes. 80% cases will die within 2 months. 10 Sv & above :Onset of diarrhea, fever in 30 minutes. G.I. Tract damage, death within 2 weeks. At 30 Sv or above death due to respiratory failure, brain damage etc. in about 2 days.  Genetic Effects Molecular changes in reproductive cells can, in principle, also affect the chromosomes and induce genetic mutation. This may result in genetic defects. High level of exposure – chance is one in hundred Moderate level of exposure – chance is one in thousand or less Low level of exposure – chance is less than one in thousand Growing fetus in mother’s womb are more sensitive to radiation. The fetus is considered as a member of the public and the dose limit for it is same as that for a member of the public.  Radiation exposure The occupational risk must be so small that it is comparable to or less than other commonly accepted industrial risks that one must tolerate in gainful employment in our safest and best managed industries. For purpose of radiation safety, the International Commission on Radiation Protection (ICRP) recognizes two categories of exposure : 1.Occupational exposure – For adults who are exposed to ionizing radiation in the course of their work. Persons in this exposure category may be called radiation workers. 2. Exposure to general public  Occupational Exposure limits Atomic Energy Regulatory Board (AERB), India has specified the following limits of radiation exposure: Refer the following link for complete details: http://www.aerb.gov.in/AERBPortal/pages/English/Constitution/directives_jsp.action 1) Annual whole body effective dose limit is 30 mSv (3 rems). 2) Cumulative effective dose for defined periods of five consecutive years should not exceed 100 mSv (10 rems). In addition to above, following Annual equivalent dose limits are also specified for some organs: Lens of the eye 150 mSv Skin 500 mSv Hands & feet 500 mSv Limits given above apply to Female workers also. However, once pregnancy is declared the equivalent dose limit to embryo/fetus shall be 1 mSv for the remainder of the pregnancy. The following figures regarding working hours have been adopted in calculations pertaining to occupational exposure: 8 hr per day x 5 days per week x 50 weeks per year.  Exposure to General public Atomic Energy Regulatory Board (AERB) has stipulated a maximum of 1mSv (100 mrem) in a year for the members of the public as the contribution from the nuclear installations in India. This effective dose limit does not include radiation dose due to natural background and the X-ray dose received from medical examination or treatment. The following Annual equivalent doses are also specified for members of the public: Lens of the eye 15 mSv Skin 50 mSv A conventional figure of 70 years has been adopted as the duration of “lifetime for non-occupational exposure”.  Types of Radiation Exposures External Radiation Exposure: Arise when radiation from a source external to the body penetrates the body and causes a dose of ionizing radiation. Exposures from gamma or x-rays, neutrons, beta particles. Dependent upon both the type and energy of the radiation. Internal Radiation Exposure Radioactive materials may be internally deposited in the body through one of the three routes of entry: Inhalation, Ingestion and Skin contact. Arise when radiation is emitted from radioactive materials present within the body. All forms of radiation (including low energy betas, gammas and alphas) can cause internal radiation exposures. Once these particles get into the body, damage can occur since there is no protective dead skin layer to shield the organs and tissues.  External Exposure Control TIME At a given radiation level and at a point the radiation dose received is directly proportional to the time spent: the less time, less dose, more the time more dose. Time limit = Dose limit/ Dose rate The units of time must be the same for the dose rate and the time limit. DISTANCE Increasing the distance between a person and the source results in a sizable reduction in the radiation exposure. If the distance is doubled, the exposure rate reduces to one fourth. This is called inverse square law. 1 Dose (or Dose Rate)  --------------------- (distance)2 External Exposure Control  External Exposure Control SHIELDING Shielding materials like lead and concrete reduces gamma radiation levels. Thickness of shield required to reduce radiation level at a given place by half is called the Half Value Layer denoted as HVL and to reduce by ten times is called Tenth Value Layer or TVL. By shielding a source the radiation level at working place can be reduced.  Protective Clothing The type of protective clothing required depends on the amount of radioactivity/radiation at the place of work. These protective clothing include lab coats, coveralls, boiler suits, aprons, full length plastic suits, shoe covers, cotton hand gloves. Handling of small amount of radioactivity will require wearing lab coats over normal attire. Where large quantities of activity are handled or where risk of contamination exists, coveralls must be used. Rubber gloves should be worn when there is a likelihood of contamination of hands. Clothing and equipment used inside radiation area must not be used in any other area.  Radiation hazards at PLF Radiation safety aspects: -unique & complex for particle accelerators. Primary particle beam produces - high dose rates over small areas near the target. Secondary radiation (bremsstrahlung, neutrons etc.) creates - medium dose rates over large area. Radiation doses to working personnel - small, - though the potential for high exposure exists. Dose Control achieved by proper planning (shielding & design aspects), practice and compliance of safety rules and procedures.  Radiation in active areas " During accelerator operation, the large amount of neutrons and gamma rays produced in active areas like Analysing Magnet vault and experimental beam halls are stopped by shield-walls and doors and hence they do not pose any radiation threat to workers." During maintenance shutdown some parts of the machine remain Radioactive due to remnant residual activity. These remnant activities pose hazards like external photon exposure and personnel contamination.  Radioactive Contamination Radioactive contamination is the deposition of radioactive material on any place or object where it is not desired to be present. If contamination is not controlled, they spread to different areas either by movement of personnel or by movement of materials, which is not desirable. TYPES OF SURFACE CONTAMINATION There are two types of surface contamination: 1) Loose or transferable and 2) Fixed. Any contamination that is transferred to another surface by applying moderate pressure is termed Loose or Transferable contamination. The radioactive contamination remaining on a surface after repeated decontamination efforts is known as Fixed contamination.  Max. Permissible Contamination level Transferable Fixed Alpha Beta-gamma Alpha Beta-gamma dpm/100cm2 dpm/100cm2 dpm/100cm2 dpm/100cm2 Floor 20 1000 2200 22000 Hands - - 4800 (Total) 24000 (Total) Skin - - 4800 (Total) 9000 Clothes : Plants - - 12000 36000 Personal - - 3000 12000 No removable or loose contamination is allowed on Hands, Skin and Clothing. Consult Health Physicist for necessary action. When small Spillage of Radioactivity Put absorbent paper immediately over the wet spill. In case of dry spill, damp down the affected area and put absorbent paper over it. Isolate the area to prevent unnecessary spread and personnel exposures. Carefully remove the absorbent papers to a suitable receptacle. Decontaminate the area until the contamination levels have been brought down to permissible level, in consultation with the health physicist. When large Spillage of Radioactivity 1) Cordon off the area and display a radiation contamination sign board at the barrier. 2) Notify all other persons in the affected area and ask them to vacate the place. 3) Persons contaminated should not proceed far into inactive area. 4) Inform Health Physicist immediately. 5) Decontaminate the contaminated people first before starting the detailed area decontamination. 6) Enter the affected area for decontamination with adequate protective Equipment. 7) Follow the instructions of Health Physics Unit regarding movement in affected area and for decontamination. Radiation Monitoring & Measurements AREA MONITORING: AREA MONITORS Area neutron and gamma monitors with read out facility, visual and audible alarms are installed in different locations at PLF. Parallel connections are given to meters having audible and visual alarms installed in Control Room panel. The radiation levels at different locations in PLF can be thus monitored from Control Room. AREA RADIATION SURVEY Routine. radiation surveys are carried out within the areas like Analysing Magnet Vault entrance, areas in the vicinity of expt. beam hall etc. to determine the adequacy of safety precautions. Necessary instructions are issued based on the survey results. Surveys in experimental beam halls are generally made after any experiment. Proper instructions are given to users based on these survey results  Personnel Monitoring Personnel monitoring is the continuous measurement of an individual’s exposure dose by means of one or more types of suitable instruments which are carried by the individual all the times. The choice of personnel monitoring instrument must be compatible with the type and energy of the radiation being measured. THERMOLUMINESCENT DOSIMETER (TLD) -For Permanent dose records of an individual. DIRECT READING POCKET DOSIMETER -For instant dose monitoring. NEUTRON BADGE -For neutron dose monitoring. Thermo-Luminescent Dosimeter (TLD) The TLD badge consists of a plastic cassette containing three TLD discs positioned over circular holes on an Aluminium card. A thin paper strip with information about the user printed on it is inserted in the badge as a wrapper over the card. These TLDs are sensitive to X-ray, Beta and gamma radiation and are useful in the dose range 0.05mSv to 10 Sv. The TLD discs in the aluminium card are read, in a TLD reader. When they are processed (heated to a temperature in TLD Reader) they emit light. The amount of light emitted is proportional to the dose received by the person in mSv.  TLD Badges – Points to note Thermoluminescent Dosimeters (TLD badges or TLD’s) should be worn by anyone working with penetrating ionising radiation to confirm acceptable levels of radiation exposure. A TLD badge should be worn only by the person to whom it has been issued. It is the responsibility of the wearer to ensure that it is returned on time. (The TLD inserts are reused by TLD section and therefore non-returned badges or those returned late attract penalty. (In extreme cases, HPU (VECC), Kolkata which is the Unit from which HPU (TIFR), Mumbai seeks broad policy guidance, has refused continuation of the service to persistent offenders in this regard.) Routinely, badges are changed at Qtrly. intervals. For those potentially more at risk from handling radioactive materials, Wrist TLD’s may be provided on prior intimation. TLD’s for visitors/external students can be obtained with a three week of prior request in Proper Form (contact HPU) subject to the fulfillment of conditions laid down by the Facility Management (in consultation with Facility HP UNIT) from time to time.  Direct Reading Pocket Dosimeters Pocket dosimeters are worn by persons who may be exposed to X- ray or gamma radiation in order to measure the actual exposure of the wearer instantly. Direct reading pocket dosimeter operates on the principle of gold- leaf electroscope. It consists of an ionizing chamber. The system is charged initially to a fixed value. The ionizing radiation annuls part of the charge. Exposure of the dosimeter to radiation can be read from the displacement of a quartz fibre over a pre-calibrated scale that can be viewed through a lens at one end of the instrument. Commonly used direct reading dosimeters have a range of 0 – 200 mR. Do not drop a pocket dosimeter. The dosimeter may go bad or may give incorrect reading.. Pocket dosimeters are issued on request from HP Unit and should be returned back at the end of the day of issue, without fail.  Neutron Badges These badges are made of special films in which the emulsion is rich in hydrogen. A hydrogenous material also surrounds the film. The Film is a CR-39 (Columbia Resin 39) film and its chemical name is Poly Allyl Diglycol Carbonate (PADC). The neutron dose is estimated from these films by counting the tracks produced due to proton recoils caused by neutrons. A reasonable estimate of dose can be made for neutrons with energies from 0.3 to 14 MeV. Apart from beam-time experiments, staff etc. are also required to handle neutron sources for calibration of nuclear detectors and for other experiments and hence are issued with Neutron Badges.  Radioactive Waste Disposal "You don't know what you throw away until you check." Proper collection and disposal of radioactive waste is an inherent part of contamination control. Hence Users are responsible to get all the material that has a potential for getting activated/contaminated during an experiment checked from the HP Unit before disposing it off. In case of active waste, the HP Unit will plan the disposal in consultation with the PLF Local Safety Committee.  Health Physics Unit " Safety consciousness should become a habit." Health Physics Unit (TIFR) is a part of Accelerator Radiation Safety Section, Health Physics Division, Bhabha Atomic Research Centre (BARC), Mumbai. The Health Physics Unit of this Facility provides radiological safety coverage during operation and maintenance of the accelerator. Routine radiation surveys are Carried out within the controlled/ supervised Areas to determine the adequacy of safety levels. All the results are recorded. Continuous monitoring of all individuals is carried out. Personnel exposure data received from Dose Records & Statistics Section, RP & AD, BARC is maintained and provided to the Regulatory Body (BARC Saftey Council). These records are also maintained in the national database of radiation doses at NODRS. “Safety is everybody’s business. Individual’s belief in Safety is vital than any statutory and administrative measure.” Radiation Safety Systems in PLF Accelerator Anil Shanbhag 1 BARC TIFR PELLETRON LINAC FACILITY - LAYOUT Anil Shanbhag 2 BARC TIFR PELLETRON LINAC FACILITY  28 modules (14 each in LE & HE section) are installed in a stainless steel tank (pressure vessel) pressurized with SF6 gas (as an insulator) at 80 psig (14.7 psi = 1 atm). Each module can withstand 1 MV in SF6 atmosphere.  The machine may be treated as a large cylindrical charged capacitor where the terminal acts as the +ve plate and the ss tank wall acts as the ground, with both the plates being separated with a dielectric material (SF6).  From the Ion-Source till the target in the beam hall, ultra high vacuum (10-8 Torr) is maintained with the help of various pumping stations. Rotary pumps (upto 10-3 Torr) & Turbo-Molecular pumps (beyond that with vanes rotating at 30-40 kRPM) are used at Ion- Source. Combination of Sublimator and Ion Pump are used throughout the accelerator. Diffusion pumps are used at the User’s end of the beam-line. Anil Shanbhag 3 BARC TIFR PELLETRON LINAC FACILITY  There are 6 Beam Profile Monitors (BPM) and 5 Faraday Cups which helps to monitor, tune and measure beam currents at various stages of the acceleration.  At the Ion-Source, singly charged -ve ions are generated. It is possible to generate beam of ions right from proton to uranium (except noble gases).  The –ve ion generated requires energy to travel from ion-source to the entry of the acceleration tube (from where acceleration starts). Hence pre-acceleration potential of (-)150 – (-) 300 kV is applied.  Mass selection is done by setting the magnetic field of the injector magnet. (eg. In case of Silicon, there are three isotopes having masses of 28, 29 & 30). So the required mass can be selected, say Si-28 (-1). As it enters the accelerator tube, due to attractive force of the terminal (which is charged to potential of “V” MV, the energy gained by the Si-28 ion is “V” MeV. Anil Shanbhag 4 BARC TIFR PELLETRON LINAC FACILITY  At the terminal, the beam is made to pass through very thin carbon stripper foils (approx. 4 µg/cm2), electrons are stripped from the singly charged -ve ions, thus generating positive Si-28 ions of various charged states. These +ve ions will now experience a repulsive force (since terminal is +ve) and gain further energy of “qV” MeV. Therefore total energy of the beam will be V+qV = V(1+q) MeV.  Charge selection is done by setting the magnetic field of the analyzing magnet. This will depend on the beam energy requirement for that particular experiment.  The beam can be switched to the required beam-line with the help of the switching magnet.  The beam can now be taken on the target for the experiment. Anil Shanbhag 5 PELLETRON CHARGING SYSTEM Link: http://www.pelletron.com/charging.htm Anil Shanbhag 6 Fundamental Principles and Logic used in design of Radiation Safety Systems in Accelerators The Essential Components of Radiation Safety Systems are broadly classified as:  Protection System (Shielding, Search & Secure system, Scram system, Door Interlocks, Audio Visual Alarm Warning System and Master Key system)  Monitoring System (Area Monitoring, Radiation Surveys, Dose Mapping and Personnel Dosimetry system) Anil Shanbhag 7 Components of Protection System Incorporated as Design Safety Features.  Shielding (Bulk & Local): Provides Safe Working Areas outside the machine containment. Shielding is designed in such a manner that the dose rates in accessible areas is less than 1 μSv/h. Further supplemented by Administrative Controls as & when required during machine operation.  Search & Secure System: This design safety feature ensures that all potential radiation areas that are not accessible during machine operation are thoroughly searched physically before starting the machine. This helps in preventing the inadvertent trapping of any individual in a high radiation area. At Pelletron, S&S are provided at 35/32m, 21m, 12m, 8/6m, 0m & Beam Hall. Anil Shanbhag 8 Components of Protection System Incorporated as Design Safety Features (Continued)  Scram System: If an individual gets trapped even after a proper search & secure procedure, this design safety feature provides the trapped individual to stop the beam at a safe location, thus preventing him/her from getting exposed to radiation. At Pelletron, Scram Buttons are provided in the Beam Hall.  Door Interlocks: This design safety feature prevents the accidental exposure to an individual who makes an inadvertent entry to a potentially hazardous area while the machine is in operation. At Pelletron, door interlocks are provided at 35/32m, 21m, 12m, 8/6m, 0m & Beam Hall. Anil Shanbhag 9 Components of Protection System Incorporated as Design Safety Features (Continued)  Audio Visual Alarm Warning System: This design safety feature generates automatic audio visual alarms and alerts the workers/users about start-up of the machine. At Pelletron, an audio visual alarm is provided in the beam hall and the beam falls on the target only after a delay of 90 seconds after the completion of the search & secure procedure followed by the closing of the beam hall entrance door. The audio-visual alarm alerts any individual who has got left inside the beam hall (in spite of a proper search & secure procedure) and the time gap of 90 seconds provides him/her with sufficient time to press the scram button for stopping the beam at a safe location, thus preventing him/her from getting exposed to radiation. Anil Shanbhag 10 Components of Protection System Incorporated as Design Safety Features (Continued)  Master-Key System: This design safety feature consists of a bunch of keys for locking the entry door to potentially hazardous areas within the accelerator block and a master key for start-up of the accelerator. If any individual requires to make an entry to any of the potential radiation areas (that are not accessible during machine operation), he/she has to turn the master key to withdraw the key bunch from the control panel, thereby ensuring stoppage of the beam at an appropriate location (with the permission of Shift-In-Charge). At Pelletron, a Master-Key system as described above is used. Anil Shanbhag 11 Components of Radiation Monitoring System Area Monitoring System:  Continuous system for the monitoring of the area radiation field should created with local read-out and remote read- out in the Control Room. A system should be created to access historical data for correlating it with the machine status/ particular experiment.  At Pelletron, Neutron & Gamma area radiation monitors are installed at three different locations namely the ion- source room, outside analyzing magnet room entrance and outside Pelletron Accelerator beam hall entrance.  Each monitor is provided with a readout facility and audio- visual alarms. Parallel read-back meters along with audio- visual alarms are also provided in the control room. Anil Shanbhag 12 Components of Radiation Monitoring System Area Monitoring System (continued):  The procedure to be followed in case of such an alarm is that the control room operator shall the call Health Physicist /RSO either over the telephone or PA system and then mute the alarm in the Control Room.  The RSO/health physicist shall survey the area of the site and take suitable remedial measures.  The alarm level is set at 1 μSv/h for area gamma monitors, which are GM counter based instruments. If the main power supply to the instrument is cut off, a visible indication is given in the control room. Anil Shanbhag 13 Components of Radiation Monitoring System Area Monitoring System (continued):  The detector of the area neutron monitor consists of a BF3 counter surrounded with 6 cm thick paraffin covered with 0.5 mm thick cadmium layer. The response of this type of moderated counter assembly is essentially independent of neutron energies up to 15 MeV.  The alarm level is set at 25 n.cm-2.s-1 for area neutron monitors.  Recently, Accelerator Interlock system (AIS) has been modified to include a neutron monitor interlock as per the directive of the regulatory body [Particle Accelerator Safety Committee (PASC)] to ensure operator safety. Anil Shanbhag 14 Components of Radiation Monitoring System Area Monitoring System (continued):  The neutron monitor at 0m level is used to achieve the intended interlock function. If the area neutron monitor reading (outside the analyzing magnet vault) exceeds 25 neutrons.cm-2.sec-1, the relay contact is activated and triggers the controller of faraday cup FC-02 and causes it go IN.  The beam is thus stopped at FC-02 which is located at a height of 35 meters above and outside the accelerator tank.  At the same time audio and visual alarm is triggered in the control room to indicate that the neutron radiation at 0 meter level had exceeded the pre-set value. Anil Shanbhag 15 Components of Radiation Monitoring System Area Monitoring System (continued):  The shift-in-charge then has to take the following actions:  Reduce the beam current from the ion source so that the neutron level reduces to less than 25 neutrons.cm-2.sec-1 at 0 meters.  Reset the neutron monitor interlock.  The neutron monitor interlock has been designed such that in case of loss of power it is triggered and causes FC- 02 to go in the IN position. On resumption of power the audio and visual alarm is triggered. The shift-in-charge then has to reset the neutron monitor interlock before being able to operate FC-02 faraday cup. Anil Shanbhag 16 Components of Radiation Monitoring System Radiation Survey:  Periodic radiation surveys under different operating parameters (beam specie, beam energy, beam current, beam line etc.) have to be carried out. Even under similar operating conditions, radiation field may vary on different days due to several beam dynamics factors. Survey Instrument should be selected depending upon the energy, pulse structure and composition of the radiation field.  At Pelletron, moderated BF3 counter (REM Counter) is utilized for the survey of neutrons. GM & Plastic Scintillator based detectors are used for the survey of photons. Anil Shanbhag 17 Components of Radiation Monitoring System Radiation Survey (continued):  The entry of the survey data and the associated observations are made in the Health Physics Log Book. The salient part of the compiled radiation survey data is sent to the regulatory body (Particle Accelerator Safety Committee, BARC Safety Council) as a part of the Qtrly. Operational Safety Report (QOSR) which is to be submitted by the OIC of the Facility (Head, Pelletron Section, NPD, BARC).  The Health Physics Unit Log Book is an important reference resource for the future since it serves as a ready access to historical data for correlating the radiation levels with the machine status/ particular experiment. Anil Shanbhag 18 Components of Radiation Monitoring System Dose Mapping:  This helps in identifying the potential locations within the accessible areas, where radiation levels may exceed 1 μSv/h during certain experiments. This also helps the accelerator operators to minimize beam losses so that the efficiency of the beam delivery on the target can be improved.  At Pelletron, experiments likely to generate dose rates in excess of 1 μSv/h in accessible areas have been identified. The locations where the dose rates exceed 1 μSv/h have also been identified. Administrative Controls like limited occupancy are put in place for such locations during such experiments. Anil Shanbhag 19 Components of Radiation Monitoring System Dose Mapping (continued):  At Pelletron, if higher than usual radiation levels (for a certain experiment) are observed as compared to a similar experiment conducted in the past, at any location in the accessible area and if the historical survey data indicates that this should not have been the case, then first the survey instrument performance is checked with known neutron & gamma sources. If the survey instruments are found to be ok, the survey is repeated with the same as well as an additional instrument. If still, higher than usual radiation levels are observed at that location, the operator/users are asked to check the beam dynamics (i.e. to ensure that there is no significant beam loss at some close-by (but un-wanted) location within the machine). Anil Shanbhag 20 Components of Radiation Monitoring System Personnel Dosimetry:  Personnel Dosimetry devices should be provided to the radiation workers (staff & users) to monitor the doses received by them. This is mandatory for ensuring compliance with the annual dose limits recommend by the regulatory body.  At Pelletron, staff & users are regularly provided with a set of TLD and FNM Badge. The badges are changed on qtrly. basis. Occasionally, DRD is also issued to certain individuals who are likely to handle hot targets etc. Anil Shanbhag 21 Types of radiation monitoring specific to Pelletron accelerator  Neutrons (mainly due to evaporation from the Compound Nucleus formation)  Gamma Rays (due to cooling of the excited compound nucleus after particle emission is no longer energetically possible). Anil Shanbhag 22 Necessary and sufficient Radiation monitoring requirements  Survey Instruments for neutrons (BF3, 3He based instruments)  Survey Instruments for gamma (GM, Plastic Scintillator, Ion Chamber based)  https://www.orau.org/ptp/collection/proportional%20counters/bf3info.htm  https://www.nde- ed.org/EducationResources/CommunityCollege/RadiationSafety/radiation_safety_equipment/Survey Meters.htm Anil Shanbhag 23  Thank you. Email: [email protected] Anil Shanbhag 24