Optimization of gamma-ray detectors in neutron-induced gamma-ray spectroscopy for geophysical applications

A logging sonde was designed for neutron-induced gamma-ray spectroscopy in a geophysics project by re-evaluating the previous design method and modifying it for an improvement. This study further considered radiation interaction with materials and detector responses. The detector responses were calculated with pulse height (f8) tallies with a Monte Carlo transport simulation code and they were compared with the flux (f4) tally results which were mainly used for the previous sonde design. Analyses were focused on gamma rays produced from neutron capture reactions with silicon, sodium, and potassium and neutron inelastic scattering reactions with oxygen in Korean geostandard formations. Simulated responses from sodium iodine (NaI), bismuth germanate (BGO), gadolinium oxyorthosilicate (GSO), and lanthanum bromide (LaBr3) detectors were studied to compare the anticipated performances of the logging sonde depending on detector materials. We attempted to determine optimal detector locations from the simulated energy spectra, in which one can observe differences in capture and inelastic scattering gamma-ray peaks depending on the given formation configurations in a clearer manner. A comprehensive evaluation on the physical properties of detectors and the simulation result tentatively concluded that GSO detectors placed at 30, 70, and 90 cm positions can efficiently collect the data of interest from the Korean geostandard formations.