A precise radiation counting instrument designed to measure radioactivity emanating from a radioactive tracer on labelled samples. Primarily used to count beta particles, the radioactive sample is dissolved or suspended in an organic scintillation fluid where the emission of a beta particle causes the liquid to emit light which is detected and counted. The instrument typically consist of vials containing the radioactive samples and scintillation fluid, and electronics. It is typically applied as a detector for radioimmunoassay or immuno-radiometric assay for clinical use.