A simple, transistorized circuit is described which analyzes the frequency composition of the photomultiplier current pulse from a phoswich scintillation counter. The circuit generates a gate waveform from the fast current pulse of an organic scintillator, but not from the slower pulse from an inorganic crystal. Such a circuit finds application when the phoswich is used to provide an anticoincidence particle shield around a &ggr;‐ray spectrometer.