Monte Carlo study of a method for lunar (surface) analysis based on spectroscopy of gamma rays following 14-MeV pulsed-neutron bombardment
In an investigation of the feasibility of analyzing the surface of the moon by gamma-ray spectroscopy techniques, Monte Carlo calculations were performed to estimate the spectral intensities of neutron-induced photons leaking from the moon surface during various time intervals following a burst of 14-MeV neutrons onto the surface. Four sets of calculations were done, all based on the lunar surface composition corresponding to an average composition of chondritic meteorites given by Urey and Craig, with varying amounts of carbon and hydrogen (or deuterium) added. The four spectra for the time interval 0-10 -6 s following the burst are all essentially the same, clearly showing the inelastic de-excitation gamma rays from O, Si, Mg, and Fe and also from C when that element was present. The spectra for later time intervals (10 -6-10 -5 s; 10 -5-10 -4 s, and 10 -4-10 -3 s) are predominantly capture spectra dominated by iron capture gamma lines at 6.0 and 7.63 MeV and by the 2.23-MeV hydrogen capture gamma line when hydrogen was present. An examination of all the spectra indicates that, providing proper calibrations are made, the abundances of the various isotopes present on the lunar surface can be determined by gamma-ray spectroscopy techniques.