A Scintillation Pair Spectrometer

Abstract

A scintillation pair spectrometer involving the use of three NaI(Tl) crystals has been developed which has a high rejection of all unwanted pulses. As in the usual scintillation pair spectrometer, the gamma rays pass into a center crystal and the pair events are selected by detecting the two annihilation quanta in two side crystals. High rejection of unwanted coincidences is obtained by using a cathode-ray tube differential discriminator set on the photoelectron peaks of the annihilation quanta in the side crystals, along with coincidence circuits of moderately good resolution (0.15 μsec). In this way pair distributions from Na24 (1.38 and 2.76 Mev) and Co60 (1.17 and 1.33) have been observed with almost no background. The apparatus has also been found useful in many other scintillation counter applications involving energy differentiation and coincidence counting.