Ionizing radiation has the same effect as light on photographic film and the extent of blackening of the film is related to the amount of radiation. Autoradiography is particularly useful for demonstrating the location of radioactive isotopes in tissues or chromatograms (Figure 5.6).
The sample is placed on a photographic film which is protected from the light and allowed to remain in contact long enough for an adequate exposure. The exposure time is dependent upon the intensity of the radiation and can usually only be determined by trial and error. It is possible, however, to predict an approximate exposure time from the fact that a total emission of 107 beta particles per square centimetre is often required.
Autoradiography is also a convenient way of monitoring the amount of radiation to which a worker has been exposed (dosimetry). If a small badge containing photographic film is worn continually and the photographic film developed after a set period of time, an estimate of the radiation received can be made from the degree of darkening of the film. No sophisticated instrumentation apart from photographic facilities are required for these types of application.
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