A Ge(Li) Concentric Duode Spectrometer for Compton Suppression

A Ge(Li) Compton sum coincidence spectrometer which greatly reduces the Compton continuum and essentially eliminates the Compton edges for low energy gammas has been fabricated. This spectrometer was made from a single cylinder of germanium in which lithium was drifted to form two separate and equal depth concentric detectors. An event in the full energy peak is recorded only if the total energy deposition occurs as the result of multiple events, with each detector sharing in the absorption process. Several types of gamma-ray spectra are presented which show the reduction of the Compton continuum. For the case of the 1275 keV gamma from 22Na the ratio of the full energy peak to Compton edge (in this case a multiple Compton event edge) increases from 2.8 to 1, when the device is used as the sum of two single spectrometers, to 13.5 to 1 when it is used in the sum coincidence mode with a decrease of efficiency of a factor of five. This ratio for the 511 keV line from 22Na increases from 3.6 to 1, to 18 to 1. Other spectra are shown and a discussion of efficiency is presented.