1. Radiation Safety Program Annual Refresher Training
Radiation Detection Instrumentation
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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.
UCLA Radiation Safety Annual Refresher Training

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.
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4. UCLA Radiation Safety Annual Refresher Training
Agenda
In this training we will cover:
Radiation detector theory
Common types of detectors at UCLA
Annual calibration requirements
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5. Radiation Detection Principles
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6. UCLA Radiation Safety Annual Refresher Training
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
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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
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Gas-Filled Detectors
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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.
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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)
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13. Gas-Filled Detector: Ionization Region
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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
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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)
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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]
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18. Gas-Filled Detector: Proportional Region
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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-
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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
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Applications
Gas-Flow Proportional
Alpha/beta counting
Tritium measurement
Air Proportional Counting
Alpha counting only
Sealed Proportional
Neutron measurement (BF3, He-3)
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22. Gas-Filled Detector: Geiger-Müller Region
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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.
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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.
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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.
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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-
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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).
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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%.
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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
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30. Scintillation Detectors
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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
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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-
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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
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34. Liquid Scintillation Counting
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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
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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
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Efficiencies
Typical efficiencies of LSC’s can be found in your Radiation Safety Journal on the Monthly Radiation Survey Report
50%
95%
95%
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38. UCLA Radiation Safety Annual Refresher Training
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
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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)
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40. UCLA Radiation Safety Annual Refresher Training
If you have any questions regarding the topics discussed during this presentation, please contact the Instrumentation Manager at ext
UCLA Radiation Safety Annual Refresher Training

41. UCLA Radiation Safety Annual Refresher Training
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.
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42. UCLA Radiation Safety Annual Refresher Training
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
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43. UCLA Radiation Safety Annual Refresher Training
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. or
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44. UCLA Radiation Safety Annual Refresher Training
Thank you for attention and congratulations on completing your annual continuing training credit with the UCLA Radiation Safety.
UCLA Radiation Safety Annual Refresher Training
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