Radiation Safety Program Annual Refresher Training

1. Radiation Safety ProgramAnnual Refresher Training Radiation Detection Instrumentation Click ‘NEXT’

2. UCLA Radiation Safety Annual Refresher Training 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.

3. Radiation Measurements 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. UCLA Radiation Safety Annual Refresher Training

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

5. Radiation Detection Principles UCLA Radiation Safety Annual Refresher Training

6. Electrical Energy 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 UCLA Radiation Safety Annual Refresher Training

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

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

9. Quantifying Radiation 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: • Detector size & shape • Detector material characteristics • Radiation energy • Probability of ionization UCLA Radiation Safety Annual Refresher Training

10. Gas-Filled Detectors UCLA Radiation Safety Annual Refresher Training

11. Gas-Filled Detectors • Comprised of: • the detector gas or gas mixtures which can be ionized • electrodes which collect the ion pairs produced from the gas • 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. UCLA Radiation Safety Annual Refresher Training

12. Ionization Curve • 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. (log scale) UCLA Radiation Safety Annual Refresher Training

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

14. Ionization Chamber • 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. High Voltage UCLA Radiation Safety Annual Refresher Training

15. Ionization Region • 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. • 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. UCLA Radiation Safety Annual Refresher Training

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

17. Radiation Exposure • When used as a survey meter, an ionization chamber’s 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: • 1 R = 2.58 x 10-4 coulombs (C) [or 2 x 108 ion pairs] UCLA Radiation Safety Annual Refresher Training

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

19. Proportional Region • 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. ß- UCLA Radiation Safety Annual Refresher Training

20. Pulse vs. Current • 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) • The size of the pulse can be used to identify the type and energy of the incident radiation • Large pulse = alpha particle • Small pulse = beta particle • Smaller pulse = gamma/x radiation UCLA Radiation Safety Annual Refresher Training

21. Applications • Gas-Flow Proportional • Alpha/beta counting • Tritium measurement • Air Proportional Counting • Alpha counting only • Sealed Proportional • Neutron measurement (BF3, He-3) UCLA Radiation Safety Annual Refresher Training

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

23. Geiger-Müller Region • 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. UCLA Radiation Safety Annual Refresher Training

24. Geiger-Müller Region • 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. UCLA Radiation Safety Annual Refresher Training

25. GM Detectors • 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. UCLA Radiation Safety Annual Refresher Training

26. GM Discharge • 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). ß- UCLA Radiation Safety Annual Refresher Training

27. Resolving Time • 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 • 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). UCLA Radiation Safety Annual Refresher Training

28. Efficiency • 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 (Emax) = 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 (Emax = 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%. 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 UCLA Radiation Safety Annual Refresher Training

30. Scintillation Detectors UCLA Radiation Safety Annual Refresher Training

31. Scintillation Detectors • 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 Scintillator Ionizing Radiation UCLA Radiation Safety Annual Refresher Training

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

33. Gamma Spectrum • 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 UCLA Radiation Safety Annual Refresher Training

34. Liquid Scintillation Counting UCLA Radiation Safety Annual Refresher Training

35. Liquid Scintillation • The scintillating material is the “cocktail” • 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 • The scintillations are captured by two PMTs UCLA Radiation Safety Annual Refresher Training

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

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

38. Annual Calibration • 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 UCLA Radiation Safety Annual Refresher Training

39. 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 • Central Services Desk hours are Monday to Friday 9:00am – 4:00pm (Closed from 11:30am – 1:00pm daily) • Phone: (310) 825-5396 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. 5-8797 UCLA Radiation Safety Annual Refresher Training

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

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. 1 Jan 2011 AE UCLA Radiation Safety Annual Refresher Training

43. If you have any questions regarding the annual refresher training requirement or need a copy of your lab group’s form, please contact your responsible health physicist or the Radiation Safety training manager at ext. 4-1876 or eesparza@ehs.ucla.edu 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. UCLA Radiation Safety Annual Refresher Training END