Detector for Low Energy Gamma-Ray Astronomy Experiment

A detector developed specifically for rocket and satellite borne low energy gamma-ray astronomy experiments is described. The detector consists of a 2" long × 1" diameter CsI(T1) crystal viewed by a single photomultiplier tube together with a 8.75" long × 5.75" diameter CsI(T1) crystal viewed by four photomultiplier tubes. The small crystal is inserted into a well of the larger crystal, the output of the smaller crystal being run in anticoincidence with the large crystal. The output from the small crystal surviving the anticoincidence circuit is fed into a pulse height analyzer. This detector and its mode of operation provides a gamma-ray spectrometer which has: angular collimation, low background sensitivity, suppression of the compton continuum and relatively high photopeak efficiency. Data on the photopeak efficiency, angular response, and suppression of the compton continuum at various energies are presented. Reasons for using anticoincidence shielding rather than bulk shielding with lead to contend with background problems are discussed.