Depth dependency of neutron density produced by galactic cosmic rays in the lunar subsurface

Ota, Shuya; Sihver, L.*; Kobayashi, Shingo*; Hasebe, Nobuyuki*

Neutron production by galactic cosmic rays (GCR) in the lunar subsurface plays an important role in the radiation environment on the surface and subsurface of the Moon and to make its accurate estimation is therefore very important for lunar and planetary nuclear spectroscopy and space dosimetry. In this work, the depth dependency of neutron production from protons and alpha particles in galactic cosmic ray (GCR) was estimated using the three-dimensional particle and heavy ion transport simulation code PHITS incorporating the latest high energy nuclear data, JENDL-HE. Our estimation of equilibrium neutron density profiles in the lunar subsurface was compared with the experimental data obtained by Apollo 17 Lunar Neutron Probe Experiment (LNPE). As the results, our calculation successfully reproduced the LNPE data within experimental errors of 15% (measurement) + 30% (systematic).