Radiation Detectors Flashcards
State the basic theory of operation of a scintillation radiation detector.
When alpha particles, beta particles, or energetic rays such as X-rays or gamma rays interact with certain materials, scintillations (light flashes) are created in the materials. These materials are known as scintillation crystals. This property is also called luminescence. A photomultiplier tube is connected to detect these flashes. The tube converts the light flashes into amplified electrical signals that can be used by a pulse amplifier to indicate radiation intensity.
State the basic theory of operation of an ion chamber radiation detector.
A cylindrical gas-filled chamber with a central electrode. , the anode, which is positively charged and collects negative charges. It is insulated from the chamber wall, the cathode, which is negatively charged and collects positive charges. A voltage is applied between the central, positively charged anode and the negatively charged chamber walls, such that the central anode is at a positive voltage relative to the chamber wall. A chargedparticle passing through the gas-filled chamber ionizes some gas atoms along its path. The negative particles (electrons) produced by ionization move toward the positively charged central anode, and the positive ions move toward the negatively charged chamber walls, thecathode. This collection of charges reduces the voltage across the capacitor, resulting in a pulse that is recorded by an electric circuit.
How are scintillation detectors useful for detecting alpha radiation?
The scintillation detector produces pulses at a ratethat is directly proportional to the frequency of the incident gamma radiation coming from the process being monitored, and pulse heights are proportional to the energy of the incident radiation. This allows scintillation detectors to be used to determine the energy, as well as the number, of the exciting particles. This is one reason scintillation detectors are commonly used and particularly useful for detecting alpha radiation.
Draw, label and explain the gas-filled detector characteristics curve.
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State the basic principles of operation of a Geiger-Mueller tube radiation detector.
Operates in the Geiger-Mueller region. The region has a high gas amplification factor, typically on the order of 10 to the 8. The output pulses are often as large as several volts, which minimizes the complexity of the externalcircuitry. The second characteristic is that the magnitude of the pulse is independent of the specific ionization of the original event. Geiger-Mueller counter is not normally used for high levels of radiation.
List the four instrument checks required prior to the use of a portable radiation monitoring instrument.
- Chick that it is within calibration by observing the calibration sticker date.2. Visual inspection of the instrument for damage.3. Instrument battery check4. Verify a source check has been performed and is current by checking the source check sticker.
List the four instrument checks required prior to the use of a portable radiation monitoring instrument.
- Check that it is within calibration by observing the calibration sticker date.2. Visual inspection of the instrument for damage.3. Instrument battery check4. Verify a source check has been performed and is current by checking the source check sticker.
List the four instrument checks required prior to the use of a portable radiation monitoring instrument.
- Check the calibration sticker date. Is it in cal?2. Visual inspection of the instrument for damage.3. Instrument battery check4. Verify a source check has been performed and is current by checking the source check sticker.
Explain the construction and basic theory of operation of a Thermoluminescent dosimeter (TLD).
They contain small chips or rods of thermoluminescentcrystals that emits light when the crystals are heated after being exposed to radiation. Done in a reader.
Explain the construction and basic theory of operation of a Thermoluminescent dosimeter (TLD).
They contain small chips or rods of thermoluminescentcrystals that emits light when the crystals are heated after being exposed to radiation. When the crystals are exposed to radiation, the radiation excites orbital electrons to a higher energy state. The electrons remaintrapped in the higher energy state due to the crystal lattice structure of the material and impurities added to the crystal.
Explain the construction and basic theory of operation of a direct reading dosimeter (DRD).
It consists of a fixed quartz electrode and a moveable quartz fiber in a metal case that serves as the outerelectrode. The moveable quartz fiber and fixed electrode are initially positively charged in relation to the external case. Since the fixed electrode and quartz fiber have identical charges and the fixed central electrode cannot move, the quartz fiber deflects away from the fixedelectrode. When the dosimeter is exposed to a gamma radiation field, (alpha and low energy beta radiation cannot pass through the metal case and neutrons do not interact significantly), the gamma radiation interacts with the metal case to produce secondary electrons. They migrate to the positively charged fixed electrode and quartz fiber, reducing their charges. The quartz fiberthen deflects back toward the fixed electrode. An internal scale allows the deflection to be interpreted as dose received.
Explain the construction and basic theory of operation of a direct reading dosimeter (DRD).
It consists of a fixed quartz electrode and a moveable quartz fiber in a metal case that serves as the outerelectrode. The moveable quartz fiber and fixed electrode are initially positively charged in relation to the external case. Since the fixed electrode and quartz fiber have identical charges and the fixed central electrode cannot move, the quartz fiber deflects away from the fixedelectrode. When the dosimeter is exposed to a gamma radiation field, (alpha and low energy beta radiation cannot pass through the metal case and neutrons do not interact significantly), the gamma radiation interacts with the metal case to produce secondary electrons. They migrate to the positively charged fixed electrode and quartz fiber, reducing their charges. The quartz fiberthen deflects back toward the fixed electrode. An internal scale allows the deflection to be interpreted as dose received.
Explain the construction and basic theory of operation of an electronic dosimeter.
They are battery-operated GM tube devices that respondto gamma and X–ray type radiation. Electronic dosimeters can measure accumulated dose and actual dose rate. Most units are autoranging with a range of μR/hour to several hundred R/hour.
Explain the construction and basic theory of operation of an electronic dosimeter.
They are battery-operated GM tube devices that respondto gamma and X–ray type radiation. Electronic dosimeters can measure accumulated dose and actual dose rate. Most units are autoranging with a range of μR/hour to several hundred R/hour.
Explain the construction and basic theory of operation of a film badge.
The badge consists of a small piece of photographic or X-ray film inserted into a metal or plastic jacket. Inside the jacket is a front and rear filter composed of lead, cadmium, or some other shielding material. Between these are inserted one or more bits of film with varyingsensitivities. In one portion of the jacket, there is a window to admit beta radiation. After the film badge has been worn for a time, the film is removed and developed by standard photographic techniques. The film will bedarkened in proportion to the amount of radiation received. Film badges do not react to alpha radiation.
