Enhancement of Compton suppression ratios in anti-Compton techniques: the Garching and Karlsruhe photon spectrometers

Two compact, high-purity germanium and sodium iodide detector systems with very high signal-to-background ratios are described. These systems are designed to identify weak photons emitted from radionuclides with single and multiple photon emissions in the presence of background radiation induced by photons of higher energy. The mounting and housing of the germanium detector are built for minimum gamma-ray absorption and is surrounded by three sodium iodide detectors. The fast and slow timing electronic circuits can be used for a wide range range of photon energies down to 10 keV, for both the pure 4π Compton suppression mode and the mixed energy and time coincidence/anticoincidence mode. The systems are also efficient for low-level spectrometry and high count rates up to 105 cps. These spectrometers exhibit Compton reduction ratios (unsuppressed/suppressed) of up to 23 for the single photon emission of 137Cs, up to 60 for the two-photon emission of 60Co, and in excess of 97 for the mixed 3- to 4-photon emission of 82Br.