Separately Housed Ge(Li) Detectors Operating in Parallel and as a Summing Compton Spectrometer

Coaxial as well as planar Ge(Li) ¿-ray detectors housed in separate cryostats have been operated in parallel and as a summing Compton spectrometer. The linear signals from two detectors were direct coupled into a single charge-sensitive preamplifier, thus eliminating the need for matching electronic gain and linearity of two separate channels. The full-energy peak efficiency of two parallel coaxial detectors is nearly equal to the sum of the efficiencies of the individual detectors. Similar increase in efficiency was also observed for double-escape peaks when two small planar detectors were paralleled. The FWHM of the 1.33 MeV 60Co line was 2.94 keV in the parallel mode as compared with 2.23 and 2.38 keV for the constituent 22cc coaxial detectors. When the latter detectors were used as a summing Compton spectrometer, the Compton edge was completely eliminated. The peak-to-Compton ratio in a 137Cs spectrum was 25:1 in the singles mode and 125:1 in the coincidence mode. However, in the complex Th C" spectrum the Compton spectrometer was not very effective in resolving a weak low energy line from the continuum of several intense ¿-rays of higher energy. Thus, one large, high resolution detector or several in parallel is not only simpler and more efficient, but may also be more effective than the summing Compton spectrometer.