The coincidence spectrometer consists of two scintillation spectrometers, each of which can be used as either a beta-ray or a gamma-ray spectrometer, depending on what crystals are used. The pulses from the first spectrometer are analyzed with a single channel analyzer. The pulses corresponding to a certain energy are picked out with the analyzer and are fed into one channel of a coincidence circuit. The pulses from the second spectrometer are fed into the other channel of the circuit. The coincidence output pulses are used to trigger an oscilloscope. The pulses from the second spectrometer are displayed on the screen of the scope. Because the scope is triggered by the coincidence circuit, only those pulses from the second spectrometer which are in coincidence with the selected pulses from the first spectrometer are seen. The pulse distribution of the displayed pulses is recorded by photographic methods. Gamma-ray spectra are recorded by taking still pictures of the screen. Beta-ray spectra are recorded by photographing the screen with a movie camera, s~ that each individual pulse is recorded separately.
Johansson, Sven A. E., "A coincidence scintillation spectrometer" (1953). Ames Laboratory ISC Technical Reports. 67.