Bombardment experiments with thick targets made of each of Al and Fe were performed using 230 MeV/nucleon helium and 210MeV proton beams. The energies and intensities of prompt gamma rays emitted by inelastic nuclear scattering of energetic neutrons were measured by a high-purity Ge detector. This work presents the first experimental results concerning the emission of prompt gamma rays from thick targets anticipated by helium component in galactic cosmic rays, since no foregoing work related to this one has been done. It is concluded that helium has the capability of prompt gamma ray line emission through the inelastic nuclear reaction of neutrons with target material by a factor of 3.5 on average in comparison with proton. As regards the lunar and planetary nuclear spectroscopy, a consideration is given on the role of helium particles to the total production of gamma rays emitted from a planetary surface.
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