Radiation detectors, a summary

Ionising radiations as normally used cannot be observed by the unaided human senses. They were discovered thanks to photographic emulsions which remain important detectors to this day, particularly in the biological sciences. There are many designs of detectors developed to respond to specific characteristics of the different types of ionising radiations discussed in earlier chapters and notably in Section 4.3.3.

Sections 5.2 and 5.3 will deal with ionisation detectors used for β and γ radiations, Section 5.4 will deal with liquid scintillation (LS) counting, adding to the material presented in Section 4.2.4. This will be followed by a description of microcalorimetry, an efficient detection method when working with high activities of many β and γ ray emitters. Section 5.4 will also cover the detection of neutrons at low and high intensities. Section 5.5 will deal with semiconductor detectors, which have long been indispensable for photon as well as for charged particle spectrometry.

Readers who seek details about specialist applications in any branch of radioactivity measurements are referred to the work of Knoll (1989), who deals with the scientific principles underlying these procedures over a broader range than other currently available textbooks.

Characteristics of ionisation detectors

Saturation currents and gas multiplication

A long established method for measuring the intensity of nuclear radiations uses their ability to ionise air or other gases such as argon or methane. Instruments that use an electric field to collect the ions and serve to measure the resultant ionisation current are known as ionisation chambers, but ionisation detectors can also be operated as pulse counters.