Radiation Detection
Human senses cannot detect radiation. A variety of handheld and laboratory instruments are available for detecting and measuring radiation.
A variety of handheld and laboratory instruments are available for detecting and measuring radiation.
The most common handheld or portable instruments are:
- Geiger Counter, with Geiger-Mueller (G-M) Tube or Probe: A G-M tube is a gas-filled device that, when a high voltage is applied, creates an electrical pulse when radiation interacts with the wall or gas in the tube. These pulses are converted and displayed on the instrument meter. These probes are most often used with handheld radiation survey instruments for contamination measurements.
- MicroR Meter, with Sodium Iodide Detector: A solid crystal of sodium iodide creates a pulse of light when radiation interacts with it. This light pulse is converted to an electrical signal by a photomultiplier tube (PMT), which reads on the instrument meter. The pulse of light is proportional to the amount of light and the energy deposited in the crystal. If the instrument has a speaker, the pulses also give an audible click, a useful feature when looking for a lost source. Sodium iodide detectors can be used with handheld instruments or large stationary radiation monitors.
- Portable Multichannel Analyzer: A sodium iodide crystal and PMT described above, coupled with a small multichannel analyzer (MCA) electronics package, are becoming much more affordable and common. When gamma-ray data libraries and automatic gamma-ray energy identification procedures are employed, these handheld instruments can automatically identify and display the type of radioactive materials present. When dealing with unknown sources of radiation, this is a handy feature.
- Ionization (Ion) Chamber: This is an air-filled chamber with an electrically conductive inner wall and central anode and a relatively low applied voltage. When primary ion pairs are formed in the air volume from x-ray or gamma radiation interactions in the chamber wall, the central anode collects the electrons. A small current is generated and measured by an electrometer circuit and displayed digitally or on an analog meter.
- Neutron REM Meter, with Proportional Counter: A proportional counter tube is a gas-filled device that, when a high voltage is applied, creates an electrical pulse when neutron radiation interacts with the gas in the tube. These charged particles can then cause ionization in the gas, collected as an electrical pulse, like the G-M tube.
Knowledge Check Choose the best answer for the question.
1-6. When dealing with unknown sources of radiation, this tool tends to be the most useful.
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