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an instrument or apparatus by which numerical value is computed; in radiology, a device for enumerating ionizing events.
Coulter counter an automated instrument for performing blood counts, based on the principle that cells are poor electrical conductors compared with saline solution.
Geiger counter (Geiger-Müller counter) a radiation counter using a gas-filled tube that indicates the presence of ionizing particles. It is very sensitive to β particles but relatively insensitive to γ and x-rays.
scintillation counter a device for detecting ionization events, permitting determination of the concentration of radioisotopes in the body or other substance.