High Energy Gamma Spectroscopy

Gamma ray energies from 50 mev to 2 bev have been measured with a total absorption method. The gamma rays produce electron showers in a transparent, high Z material. A photomultiplier views the visible light produced, due either to Cerenkov radiation or scintillation. Limits on the energy resolution of this device are the loss of part of the shower from the sides and end, varying efficiency of light collection from different parts of the material, and pauclty of Cerenkov photons when that technique is used. Factors involved in choosing the material and shape of the shower producer will be discussed. Because of the small size and high efficiency, this type of spectrometer is very useful for experiments with high energy accelerators. Descriptions and characteristics of several versions of this instrument are given.