Experimental simulations of planetary gamma-ray spectroscopy using thick targets irradiated by protons

To simulate planetary gamma-ray spectroscopy, gamma rays were measured during a series of five irradiations of up to 30-ton thick targets with protons beams of 1.5 and 2.5 GeV. The targets were steel (iron), basalt with structural steel, basalt with added S and Cl, and basalt with added H, S, and Cl. The pulsed proton beam was carefully monitored and counted. Spectra were collected with both proton beam on and beam off and with a lead shield both between the target and the germanium detector and with the lead shield removed. This set of four spectra was used to determine the fluxes of prompt gamma rays emitted from the target. Over 200 discrete gamma-ray lines per irradiation were observed and identified. Counting results for the more intense gamma rays were compiled, and gamma-ray fluxes determined for about 25 gamma rays of interest to planetary gamma-ray spectroscopy. The ratios of thermal and fast neutron induced gamma-ray fluxes between irradiations were similar. Thus the relative gamma-ray fluxes can be used in testing model calculations and interpreting planetary gamma-ray spectra.