Simulation of 4π Ge Spectrometer by Geant4.

We are developing a 4π Ge-spectrometer for the measurement of neutron capture cross sections of minor actinides. The 4π Ge-spectrometer consists of Ge detectors that cover a large solid angle of a sample; the spectrometer has high efficiency and good energy resolution for γ-ray detection. This feature enables us to discriminate desired events from backgrounds based on the measurement of total excitation energy following the neutron capture reaction. In this work, we determined an optimal configuration and evaluated performances of 4π Ge-spectrometer using a Geant4 simulation. From comparison of performances, two configurations that have uniform count rates or a high efficiency were determined. Therefore one of the two configurations is used properly to reduce an experimental error for the neutron capture cross section. Further simulations were made with a full geometry including BGO shields; absolute efficiency for the high-efficiency configuration was estimated to be 15% for a 1-MeV γ ray. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]