A Stabilized Scintillation Counter

A gain stabilization system for use with a scintillation counter is described. The system uses a Po210 α source sandwiched between two 0.020" thick discs of plastic phosphor as a reference light source, which is mounted between the NaI(Tl) crystal and the photomultiplier. This produces a stable Gaussian reference peak in the pulse height distribution, equivalent to 150 keV γ rays. A simple pulse shape discrimination circuit at the photomultiplier anode gates the circuitry such that it only responds to the reference pulses, thus making the system independent of any changes in the γ ray flux.