Earth Planets Space, Vol. 60 (No. 4), pp. 313-319, 2008
Naoyuki Yamashita1, Nobuyuki Hasebe1, Takashi Miyachi1, Masanori Kobayashi2, Osamu Okudaira1, Shingo Kobayashi1, Takeshi Ishizaki1, Kunitomo Sakurai1, Mitsuhiro Miyajima1, Robert C. Reedy3, Claude d'Uston4, Sylvestre Maurice4, and Olivier Gasnault4
1Research Institute for Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555 Japan
2Nippon Medical School, 2-297-2 Kosugicho, Nakahara, Kawasaki, Kanagawa 211-0063 Japan
3Institute of Meteoritics, University of New Mexico, Albuquerque, NM 87131-1126 USA
4Centre d'Etude Spatiale des Rayonnements, 9 avenue Colonel Roche, B.P. 4346, 31028 Toulouse cedex 4, France
(Received March 19, 2007; Revised October 20, 2007; Accepted October 20, 2007; Online published April 9, 2008)
Assuming different abundances of the Apollo lunar soil samples and the average spectrum of galactic cosmic ray protons, energy spectra of neutrons and gamma rays and emission rates of gamma-ray lines from major elements have been estimated by using the reviewed Monte Carlo simulation library Geant4 and nuclear data. Previously, such libraries were not able to reproduce gamma-ray lines properly for the planetary application. Results clearly show that the emission rate of gamma rays heavily depends not only on the chemical abundance but also neutron flux within the lunar subsurface. While the intensities of gamma-ray lines are mostly proportional to elemental abundances, the intensity per unit elemental abundance can vary. Such a complex correlation is attributed to the change in neutron flux within the lunar subsurface and petrological restriction of elemental variation.
Key words: Gamma ray, neutron, lunar and planetary spectroscopy, moon, GRS, SELENE.