Figure 10.5
Growth and decay of a radionuclide (T = t1/2).10.2—
Instrumentation and Measurement of Radioactivity
In all except autoradiography which is a special case to be considered separately, radioactive emissions
are measured by causing them to activate a detector from which a series of electrical pulses are
generated. If the sample is maintained in a fixed relationship to the detector, the number of pulses
generated within a known time, i.e. the count, will be a measure of the radioactivity. With calibration
using standard sources, the proportionality between the activity of the source and the count may be
determined. In certain circumstances the height (size) of the pulses generated is directly proportional to
the energy of the incident particles or photons. Pulse height analysis can thus be applied to distinguish
between different emissions and radionuclides. The general layout of a counting system is summarized
in Figure 10.6. α-emitting tracers are rarely used and subsequent attention will focus on β– and γ
detection.
Figure 10.6
Schematic layout of radiation detection and measurement.