Anti-Compton shield for COMPEX germanium detector modules

A bismuth-germanate (BGO) anti-Compton shield (ACS) for COMPEX germanium detector modules was designed, built, and characterised. BGO performance was evaluated for light output and energy resolution. The response of the ACS shield and its impact on germanium detector spectra was measured for standard 60Co, 133Ba, and 137Cs sources. The results were compared to comprehensive Geant4 simulations. The similar to 70% improvement of the peak-to-total ratio for the 137Cs 662-keV y-ray peak is in good agreement with expectations from the simulations. A 133Ba source exemplifies decay schemes of odd-A superheavy nuclei. Congruence between measured and simulated spectra indicates that the COMPEX plus ACS multi-detector module is well understood.