Gamma counter

A gamma counter is a machine to measure gamma radiation emitted by a radionuclide. They are usually scintillation counters. In a typical system, a number of samples are placed in sealed vials or test tubes, and moved along a track. One at a time, they move down inside a shielded detector, set to measure specific energy windows characteristic of the particular isotope. Within this shielded detector there is a scintillation crystal that surrounds the radioactive sample. Gamma rays emitted from the radioactive sample interact with crystal, which are then absorbed and light is the product. If the photon has too low of an energy level it will be absorbed into the scintillation crystal and never be detected. If the photon has too high of an energy level the photons may just pass right through the crystal. Thus the thickness of the crystal is very important when sampling radioactive materials using the Gamma Counter.^[1][2] Depending on the half-life and concentration of the sample, measurement times may vary from 0.02 minutes to several hours. Gamma counters are standard tools used in the research and development of new radioactive compounds used for diagnosing and treating disease, (as in PET scanning). Gamma counters are used in radiobinding assays,^[3] radioimmunoassays (RIA) and Nuclear Medicine measurements such as GFR^[4] and hematocrit.^[5]

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