A Ge/Li/ spectrometer for gamma ray astronomy

A space-borne instrument to measure the spectral and temporal characteristics of astronomical gamma rays in the .05 to 10 Mev energy range is described. The spectrometer consists of four 60 cc Ge(Li) detectors with an energy resolution of 2.5 Kev (FWHM) at 1.33 Mev. The Ge(Li) detectors are actively shielded with CsI(Na) for angular collimation and background reduction. Cooling of the Ge(Li) detectors to 88 K for orbital lifetimes of up to two years is provided by a two-stage solid subliming refrigerator.