Instrumentation for Medium Energy Gamma-Ray Scattering Measurements

Abstract

A system for the energy analysis of scattered gamma rays of up to 70‐Mev energy is described. A 5‐in. diam, 4‐in. long NaI(Tl) crystal was the energy sensitive element. The net amplification between the ten‐stage photomultiplier output and the pulse‐height analyzer input was 1.8. The pulse‐height‐to‐channel transfer characteristic of the system departs from linearity by less than 0.05 channel between the 50th and 16th channel and by one channel between the 16th and sixth. It is demonstrated that the light‐to‐voltage transfer characteristic of the photomultiplier is linear up to at least 30‐v output levels. Provision for direct determination of the effect of superposed pulses (pileup) is incorporated into the system. Careful shaping of the pulses reduced pileup to a minimum, commensurate with obtaining good resolution from the NaI(Tl) crystal. Some typical pulse‐height spectra are given, and the novel features of the circuits are described.