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3.8.2 Display and recording equipment

Radiation detectors are connected to electronic devices to:

  • Provide a source of power for detector operation;
  • Enable measurement of the quantity and/or quality of the radiation interactions that are occurring in the detector.

The quality of the radiation interaction refers to the amount of energy transferred to the detector. In many cases, radiation interacts with other material (e.g., air) prior to interacting with the detector, or only partially interacts with the detector (e.g., Compton scattering for photons). Because the energy recorded by the detector is affected, there is an increased probability of incorrectly identifying the radionuclide.

The most common recording or display device used for portable radiation measurement systems is a ratemeter – analog or digital. This device provides a display representing the number of events occurring over some time period (e.g., counts per minute). The number of events can also be accumulated over a preset time period. The resulting information from a scaling device is the total number of events that occurred over a fixed period of time, where a ratemeter display varies with time and represents a short term average of the event rate. Determining the average level on a ratemeter will require judgment by the user, especially when a low frequency of events results in significant variations in the meter reading.

Pulse height analyzers are specialized electronic devices designed to measure and record the number of pulses or events that occur at different pulse height levels. These types of devices are used with detectors which produce output pulses that are proportional in height to the energy deposited within them by the interacting radiation. They can be used to record only those events occurring in a detector within a single band of energy or can simultaneously record the events in multiple energy ranges. In the former case, the equipment is known as a single-channel analyzer; the latter application is referred to as a multi-channel analyzer.