REVISION/USAGE LOG REVISION NUMBER DESCRIPTION OF CHANGES DATE PAGES AFFECTED REVIEWED BY 0 Initial issue 1 General revision to enable lesson plan to be used as initial training and continuing training and to incorporate 10CFR20 changes. Body 1-56 Attach. 1: 1-3 Attach. 2: 1-4 Add attachment 3, “Portable Instrument Lab” Note – HPT001.021A can be used to track and award credit for Attachment 2. Verified technical accuracy; minor editorial adjustments. All All BAB Brian Fike 2 General Revision. Deleted Portable Instrument Lab. Deleted specifications on EDs as another lesson includes this. objective on thermoluminescense for continuing training. All Amy E. Burzese 3 General revision to update material for reactivation of initial training program. All C. Daphne Stephens 4 Added a 4 hour length for continuing training 3 Mahlon Tuck
5. Neutron Detection and Measurement a. Fission chambers are basically ion chambers with a fissionable material coating on the inner wall. b. Neutron detectors used for dose rate monitoring rely on nuclear reactions which result in charged particles such as protons or alpha particles. Used for neutron flux monitoring. D. Gas Filled Detectors 1. Types of Gas Filled Detectors: a. Ionization. b. Proportional. c. Geiger-Mueller. 2. Simple Gas Filled Detectors a. Detector consists of an air or gas filled chamber. b. Radiation forms ion pairs in the gas. Objective B.2 HO-3 Slide 1, Slide 2, and Slide 3 c. The detector has two electrodes. - positive charged center wire. cathode - negative charged chamber wall. d. The potential difference between the electrodes produces an electric inside the chamber. The anode is well insulated from the chamber wall.
e. The electric field between the anode and the cathode draws the ions toward the electrodes. (1) Positive ions are drawn to the cathode. (2) Electrons (negative charge) are to the anode. Objective B.2 f. A charge collects on the electrode causing a voltage change in the circuit (pulse). g. The pulse causes a current to flow in the meter. h. The amount of current flow is representative of the energy and amount of radiation that caused the ionization in the detector. 3. Factors That Affect The Number of Ions Pairs Created In A Gas Filled Detector: a. Type of radiation. b. Energy of the radiation. c. Quantity of radiation. d. Detector size and shape. e. Pressure and type of fill gas. f. Voltage potential across the electrodes. Objective B.3
(5) The advantages of detectors operating in the ionization region are: (a) Less regulated, less expensive, and more portable power supplies can be used. (b) The ion chamber response is directly proportional to the dose rate. Objective B.6.a Output current is independent of operating voltage. The preferred instrument for setting dose rates. (c) The number of primary ions is a function of the energy deposited in the detector by the radiation. (d) Very accurate. (e) Rugged. Objective B.6.a
(3) The ions are able to further ionization and these secondary ions continue to create ion pairs in a multiplicative process called an avalanche. (4) The gas amplification is proportional to the applied voltage. Objective B.5.b Gas amplification. (5) The gas amplification is responsible for the formation of a pulse. (6) Since the individual pulse can be measured it, is possible to distinguish radiation types. (7) It takes time for the ions to be collected and for the pulse to be generated. Likewise, it takes time for the pulse to decay. If another ionizing event occurs during this period, the ions from the second event will be collected along with the remaining ions from the first event. The resulting pulse may not be distinguishable as two pulses by the electronics. The reading will underestimate the actual radiation field.
3. Pocket chambers work on the principle of electrostatic discharge, similar to a gold-leaf electroscope. 4. The dosimeter consists of a small air-filled chamber in which a split quartz fiber is suspended. One side is fixed and the side is free to move. 5. The movable is displaced electrostatically by charging it. a. As both fibers are connected, they have the same charge and repel. b. Exposure to ionizing radiation will neutralize some of the charge, allowing the movable fiber to move towards its normal position. This movement is read on the scale. 6. Characteristics of Pocket Chambers a. Measure only X-rays or gammas. b. They are very sensitive to shock and will often go offscale if dropped. c. They are affected by humidity and geotropism d. They are subject to drift, a gradual loss of charge without the presence of radiation.
c. High voltage power supply – moves the charged particles. d. Pre-amp – converts the electrons to a shapes the pulse, and amplifies the signal. e. Amplifier- shapes and further amplifies the signal. f. Analog to Digital converter – converts the signal to digital values. The digital values become a memory location, channel, in the multi-channel analyzer. g. Multi-channel analyzer – analyzes the values in the channels and creates a spectrum that is processed by software to identify the radionuclide that emitted the incident gammas. Objective B.22 7. Spectroscopy Equipment Operational Checks a. Energy calibration – relates the energy of the gamma to a channel number. Performed during initial setup, after replacement of major components, or if unsatisfactory Method Quality Assurance, MQA, performance results are obtained. Objective B.23 Puts known peak in known channel. MQA is performed once every 6 months.