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Radiation Detection Instrumentation Radiation Safety Program Annual Refresher Training Click NEXT.

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1 Radiation Detection Instrumentation Radiation Safety Program Annual Refresher Training Click NEXT

2 UCLA Radiation Safety Annual Refresher Training Personnel working with radioactive materials are required to complete annual refresher training and submit documentation of completion to Radiation Safety by the end of the calendar year. This module may be used as one option for completion. Annual Refresher Training

3 UCLA Radiation Safety Annual Refresher Training Humans do not possess the ability to detect ionizing radiation with their 5 senses. Therefore, we must rely on instrumentation for both the detection and measurement of ionizing radiation. Radiation Measurements

4 In this training we will cover: Radiation detector theory Radiation detector theory Common types of detectors at UCLA Common types of detectors at UCLA Annual calibration requirements Annual calibration requirements Agenda UCLA Radiation Safety Annual Refresher Training

5 Radiation Detection Principles UCLA Radiation Safety Annual Refresher Training

6 There are several common sources of electrical energy such as friction, heat, pressure, and magnetism. Ionizing radiation is also a source of electrical energy and can be used to quantify radioactivity Radioactive decay products such as alphas, betas, and gammas Radioactive decay products such as alphas, betas, and gammas Electrical Energy UCLA Radiation Safety Annual Refresher Training

7 There are 3 elements to a radiation detection system: Measurement/Detection Measurement/Detection Dependent on radiation type & intensity Dependent on radiation type & intensity Detector function Detector function Interaction between detector material and incident radiation to produce an observable effect Interaction between detector material and incident radiation to produce an observable effect Readout circuitry Readout circuitry Analyzes the produced effect Analyzes the produced effect Radiation Detection Systems UCLA Radiation Safety Annual Refresher Training

8 Ionization detectors (gas-filled or solid) Ionization detectors (gas-filled or solid) Incident radiation creates ion pairs in the detector material Incident radiation creates ion pairs in the detector material Excitation detectors Excitation detectors Incident radiation excites the atoms in the detector material and emits visible light Incident radiation excites the atoms in the detector material and emits visible light Detector Types UCLA Radiation Safety Annual Refresher Training

9 As all detectors measure radiation as a function of its observed effects, a correlation must be made between the effect and the incident radiation. Factors that affect this correlation are: Factors that affect this correlation are: Detector size & shape Detector size & shape Detector material characteristics Detector material characteristics Radiation energy Radiation energy Probability of ionization Probability of ionization Quantifying Radiation UCLA Radiation Safety Annual Refresher Training

10 Gas-Filled Detectors UCLA Radiation Safety Annual Refresher Training

11 Comprised of: Comprised of: the detector gas or gas mixtures which can be ionized the detector gas or gas mixtures which can be ionized electrodes which collect the ion pairs produced from the gas electrodes which collect the ion pairs produced from the gas high voltage supply that amplifies the signal high voltage supply that amplifies the signal In a gas-filled detector, it is the magnitude of the voltage placed between the electrodes that will determine the type of response to each radiation particle or photon. In a gas-filled detector, it is the magnitude of the voltage placed between the electrodes that will determine the type of response to each radiation particle or photon. Gas-Filled Detectors UCLA Radiation Safety Annual Refresher Training

12 As the applied voltage is increased from zero to a large value, a characteristic curve will result and is given below. Three gas-filled radiation detectors have been developed based on the three usable regions labeled on the figure. The 3 usable regions on this curve are Ionization, Proportional and Geiger-Müller. As the applied voltage is increased from zero to a large value, a characteristic curve will result and is given below. Three gas-filled radiation detectors have been developed based on the three usable regions labeled on the figure. The 3 usable regions on this curve are Ionization, Proportional and Geiger-Müller. Ionization Curve UCLA Radiation Safety Annual Refresher Training (log scale)

13 Gas-Filled Detector: Ionization Region UCLA Radiation Safety Annual Refresher Training

14 At relatively low voltages, many of the ion pairs produced in an ion chamber will simply recombine, leaving no charge flow between the electrodes At relatively low voltages, many of the ion pairs produced in an ion chamber will simply recombine, leaving no charge flow between the electrodes As the voltage is increased, a certain point is reached where 100% of the ions produced will reach the electrodes. This plateau region is referred to as the ionization region. As the voltage is increased, a certain point is reached where 100% of the ions produced will reach the electrodes. This plateau region is referred to as the ionization region. Ionization Chamber UCLA Radiation Safety Annual Refresher Training High Voltage

15 In this region, the number of ions collected by the electrode will be equal to the number produced by the primary ionization event. Further small increases in voltage have no effect on the current produced in the detector. In this region, the number of ions collected by the electrode will be equal to the number produced by the primary ionization event. Further small increases in voltage have no effect on the current produced in the detector. The current is, however, affected by the type of radiation and subsequently, the quantity of energy deposited by that radiation event. The current is, however, affected by the type of radiation and subsequently, the quantity of energy deposited by that radiation event. For example, an alpha particle, because of its charge and mass, will produce many ion pairs while traveling only a short distance in the gas. Photons, on the other hand, carry neither charge nor mass and will create fewer ion pairs. For example, an alpha particle, because of its charge and mass, will produce many ion pairs while traveling only a short distance in the gas. Photons, on the other hand, carry neither charge nor mass and will create fewer ion pairs. Ionization Region UCLA Radiation Safety Annual Refresher Training

16 Ionization chambers have many applications including: Ionization chambers have many applications including: dose calibrators pocket dosimeters survey meters (Images not to scale) Ion Chamber Applications UCLA Radiation Safety Annual Refresher Training

17 When used as a survey meter, an ionization chambers current reading is typically used to measure radiation exposure and is commonly expressed in units of Roentgens (R) per hour When used as a survey meter, an ionization chambers current reading is typically used to measure radiation exposure and is commonly expressed in units of Roentgens (R) per hour The Roentgen is defined as the number of ionizations produced per kilogram of dry air under standard temperature and pressure where: The Roentgen is defined as the number of ionizations produced per kilogram of dry air under standard temperature and pressure where: 1 R = 2.58 x coulombs (C) [or 2 x 10 8 ion pairs] 1 R = 2.58 x coulombs (C) [or 2 x 10 8 ion pairs] Radiation Exposure UCLA Radiation Safety Annual Refresher Training

18 Gas-Filled Detector: Proportional Region UCLA Radiation Safety Annual Refresher Training

19 Proportional counters operate under the principle of gas multiplication. As the voltage is increased past the ionization region, ion pairs created by the incident radiation produce secondary ion pairs due to the applied electric field in the chamber. Proportional counters operate under the principle of gas multiplication. As the voltage is increased past the ionization region, ion pairs created by the incident radiation produce secondary ion pairs due to the applied electric field in the chamber. Proportional Region UCLA Radiation Safety Annual Refresher Training ß-ß-ß-ß-

20 The proportional counter is operated to detect all ion pairs generated from the incident radiation and count as a single pulse The proportional counter is operated to detect all ion pairs generated from the incident radiation and count as a single pulse Ionization chambers, as discussed earlier, count each individual ion pair collected (current) Ionization chambers, as discussed earlier, count each individual ion pair collected (current) The size of the pulse can be used to identify the type and energy of the incident radiation The size of the pulse can be used to identify the type and energy of the incident radiation Large pulse = alpha particle Large pulse = alpha particle Small pulse = beta particle Small pulse = beta particle Smaller pulse = gamma/x radiation Smaller pulse = gamma/x radiation Pulse vs. Current UCLA Radiation Safety Annual Refresher Training

21 Gas-Flow Proportional Gas-Flow Proportional Alpha/beta counting Alpha/beta counting Tritium measurement Tritium measurement Air Proportional Counting Air Proportional Counting Alpha counting only Alpha counting only Sealed Proportional Sealed Proportional Neutron measurement (BF 3, He-3) Neutron measurement (BF 3, He-3) Applications UCLA Radiation Safety Annual Refresher Training

22 Gas-Filled Detector: Geiger-Müller Region UCLA Radiation Safety Annual Refresher Training

23 By continuing to increase the voltage above the proportional region, a point is reached where the detector experiences a massive amount of gas multiplication and creates a very large output pulse. By continuing to increase the voltage above the proportional region, a point is reached where the detector experiences a massive amount of gas multiplication and creates a very large output pulse. Geiger-Müller Region UCLA Radiation Safety Annual Refresher Training

24 This area of operation is known as the Geiger-Müller region. The size of the large output pulse is independent of the amount of ionization produced by the incoming radiation. In other words, the pulse is the same regardless of the type of radiation (i.e. alpha, beta, or gamma). The advantage is that the signal amplitude is large so that no amplifiers are needed. This area of operation is known as the Geiger-Müller region. The size of the large output pulse is independent of the amount of ionization produced by the incoming radiation. In other words, the pulse is the same regardless of the type of radiation (i.e. alpha, beta, or gamma). The advantage is that the signal amplitude is large so that no amplifiers are needed. Geiger-Müller Region UCLA Radiation Safety Annual Refresher Training

25 Detectors operating in the region are called Geiger-Müller (GM) detectors. They are simple to use and can detect radiation at very low radiation levels due to their large charge amplification. A primary purpose of G-M detectors is the detection of surface contamination from beta-emitting isotopes like C-14, P-32, and S-35. Detectors operating in the region are called Geiger-Müller (GM) detectors. They are simple to use and can detect radiation at very low radiation levels due to their large charge amplification. A primary purpose of G-M detectors is the detection of surface contamination from beta-emitting isotopes like C-14, P-32, and S-35. GM Detectors UCLA Radiation Safety Annual Refresher Training

26 Similar to proportional detectors, when radiation is captured by a GM tube, ionization along the path of the incident radiation results in large gas multiplication (avalanche). Similar to proportional detectors, when radiation is captured by a GM tube, ionization along the path of the incident radiation results in large gas multiplication (avalanche). GM Discharge UCLA Radiation Safety Annual Refresher Training ß-ß-

27 These avalanches require some quenching material in the gas in order for the ion pairs to recombine and allow for detection of another radiation event These avalanches require some quenching material in the gas in order for the ion pairs to recombine and allow for detection of another radiation event The time it takes for the detector gas to reset is called the resolving time The time it takes for the detector gas to reset is called the resolving time Sometimes, in high radiation fields, the pulses generated will be too low due to the resolving time losses that the meter will effectively read zero and cease to respond to radiation (saturation). Sometimes, in high radiation fields, the pulses generated will be too low due to the resolving time losses that the meter will effectively read zero and cease to respond to radiation (saturation). Resolving Time UCLA Radiation Safety Annual Refresher Training

28 The efficiency of the G-M detector is affected by the energy of the radiation being detected. Low energy beta emitters, like H-3 (Maximum energy (E max ) = 18.6 keV), possess insufficient energy to penetrate the mica window and, thus, cannot be detected by a G-M detector The efficiency of the G-M detector is affected by the energy of the radiation being detected. Low energy beta emitters, like H-3 (Maximum energy (E max ) = 18.6 keV), possess insufficient energy to penetrate the mica window and, thus, cannot be detected by a G-M detector For practical purposes, C-14 (E max = 156 keV) is the lowest energy beta emitter that can be quantified with a G-M detector. For practical purposes, C-14 (E max = 156 keV) is the lowest energy beta emitter that can be quantified with a G-M detector. Due to the uncharged nature of photons, the efficiency of G-M detectors to detect photons is quite low. As a result, G-M detectors should not be used to quantify I-125 as the measured efficiency for this isotope is far less than 1%. Due to the uncharged nature of photons, the efficiency of G-M detectors to detect photons is quite low. As a result, G-M detectors should not be used to quantify I-125 as the measured efficiency for this isotope is far less than 1%. Efficiency UCLA Radiation Safety Annual Refresher Training

29 Practical Uses On the other hand, due to the low efficiency and directional design of GM detectors, they can be useful for qualitatively measuring gamma contamination in high background areas On the other hand, due to the low efficiency and directional design of GM detectors, they can be useful for qualitatively measuring gamma contamination in high background areas UCLA Radiation Safety Annual Refresher Training

30 Scintillation Detectors UCLA Radiation Safety Annual Refresher Training

31 Scintillations are small flashes of light that are emitted when certain materials, for example NaI(Tl), absorb radiation Scintillations are small flashes of light that are emitted when certain materials, for example NaI(Tl), absorb radiation These materials, called scintillators, are commonly used to detect gamma or X radiation These materials, called scintillators, are commonly used to detect gamma or X radiation Scintillation Detectors UCLA Radiation Safety Annual Refresher Training Scintillator Ionizing Radiation

32 The scintillations can be captured by a photomultiplier tube (PMT) and converted to electrons which are used to quantify incident radiation The scintillations can be captured by a photomultiplier tube (PMT) and converted to electrons which are used to quantify incident radiation Photomultiplier Tubes UCLA Radiation Safety Annual Refresher Training PMT e-e- Scintillator Ionizing Radiation

33 An important feature of scintillation detectors is that the energy deposited into the crystal is directly proportional to the voltage generated through the circuitry; thus, an energy spectrum can be plotted An important feature of scintillation detectors is that the energy deposited into the crystal is directly proportional to the voltage generated through the circuitry; thus, an energy spectrum can be plotted Gamma Spectrum UCLA Radiation Safety Annual Refresher Training

34 Liquid Scintillation Counting UCLA Radiation Safety Annual Refresher Training

35 The scintillating material is the cocktail The scintillating material is the cocktail Cocktails used in scintillation counting are typically biodegradable but can sometimes contain an aromatic solvent (toluene or benzene) Cocktails used in scintillation counting are typically biodegradable but can sometimes contain an aromatic solvent (toluene or benzene) Samples are dissolved or suspended in the cocktail Samples are dissolved or suspended in the cocktail The scintillations are captured by two PMTs The scintillations are captured by two PMTs Liquid Scintillation UCLA Radiation Safety Annual Refresher Training

36 Because the detector is in direct contact with the sample, the Liquid Scintillation Counter (LSC) is the only instrument that can efficiently detect tritium Because the detector is in direct contact with the sample, the Liquid Scintillation Counter (LSC) is the only instrument that can efficiently detect tritium Tritium (H-3) UCLA Radiation Safety Annual Refresher Training

37 Typical efficiencies of LSCs can be found in your Radiation Safety Journal on the Monthly Radiation Survey Report Typical efficiencies of LSCs can be found in your Radiation Safety Journal on the Monthly Radiation Survey Report Efficiencies 50%95% 95% UCLA Radiation Safety Annual Refresher Training

38 According to Title 17 California Code of Regulations §30275(b), each user shall perform or cause to have performed such reasonable tests for the protection of life, health, or property According to Title 17 California Code of Regulations §30275(b), each user shall perform or cause to have performed such reasonable tests for the protection of life, health, or property These tests are performed or coordinated through an outside vendor by UCLA Radiation Safety on an annual basis to ensure accuracy and precision of radiation detection and monitoring instruments These tests are performed or coordinated through an outside vendor by UCLA Radiation Safety on an annual basis to ensure accuracy and precision of radiation detection and monitoring instruments Annual Calibration UCLA Radiation Safety Annual Refresher Training

39 Instruments can be dropped off at the UCLA Radiation Safety Central Services Desk Instruments can be dropped off at the UCLA Radiation Safety Central Services Desk UCLA Radiation Safety Central Services Desk is located in CHS A6- 060C near the A-level loading dock UCLA Radiation Safety Central Services Desk is located in CHS A6- 060C near the A-level loading dock Central Services Desk hours are Monday to Friday 9:00am – 4:00pm (Closed from 11:30am – 1:00pm daily) Central Services Desk hours are Monday to Friday 9:00am – 4:00pm (Closed from 11:30am – 1:00pm daily) Phone: (310) Phone: (310) Central Services Desk UCLA Radiation Safety Annual Refresher Training

40 If you have any questions regarding the topics discussed during this presentation, please contact the Instrumentation Manager at ext

41 Training Record Form UCLA Radiation Safety Annual Refresher Training In order to satisfy your annual refresher training requirement, your lab group must submit the current years Principal Radiation Worker Training Record Form. This form must be sent to Radiation Safety before the end of the fall quarter.

42 Beside your name, mark the O for OTHER, date, and initial the form. If one of the workers listed is no longer with UCLA, please indicate the termination date for the worker under the column outlined. UCLA Radiation Safety Annual Refresher Training 1 Jan 2011AE

43 If you have any questions regarding the annual refresher training requirement or need a copy of your lab groups form, please contact your responsible health physicist or the Radiation Safety training manager at ext or UCLA Radiation Safety Annual Refresher Training

44 Thank you for attention and congratulations on completing your annual continuing training credit with the UCLA Radiation Safety. END


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