Detector unit with reference radiation source

A configuration is claimed of the detector unit and the reference source for instruments for automatic counting of samples labelled with radionuclides in automated gamma detectors or scintillation spectrometers. The reference source case is placed in a shaft that passes through the detector well. A cartridge with cuvettes containing the samples is placed under the reference source. The case with the reference source is pushed outside the calibration position when a cuvette with sample is inserted. Thus, no separate plug-in mechanism is needed for source motion. In the absence of a sample the measuring path is automatically stabilized. (M.D.). 2 figs