scintillation counter (scintillometer) An instrument which measures gamma radiation and is extensively used in airborne and ground radiometric surveys. It utilizes the flash of light emitted when the atoms of a suitable ‘phosphor’ (e.g. a large sodium iodide crystal ‘doped’ with thallium) are energized by gamma rays. The scintillations are detected by the light-sensitive cathode of a photomultiplier tube and are converted by the succession of electrodes in the tube into a stream of electrons which are collected and recorded on a meter. The scintillation counter has now been developed into the gamma-ray spectrometer (see GAMMA-RAY SPECTROMETRY) for portable and airborne use. It analyses the complex gamma-ray spectrum of uranium, thorium, and potassium, and indicates the relative gamma-ray contribution of each element to ground gamma-ray emission on a continuous readout.

scintillation counter A type of particle or radiation counter that makes use of the flash of light (scintillation) emitted by an excited atom falling back to its ground state after having been excited by a passing photon or particle. The scintillating medium is usually either solid or liquid and is used in connection with a photomultiplier, which produces a pulse of current for each scintillation. The pulses are counted to enable the radioactivity of the source to be calculated. The distribution of a radiolabelled compound, such as a drug, in an organism can be determined in this way by testing tissue samples from different organs after drug administration.