Neutron Production in the Lunar Subsurface from Galactic Cosmic Rays

Paper in proceeding, 2009

The neutron production from galactic cosmic ray (GCR) protons and alpha particles in the lunar subsurface was estimated using the three-dimensional Monte Carlo simulation code PHITS. The PHITS simulations of equilibrium neutron density profiles in the lunar subsurface were compared with experimental data by the Apollo 17 Lunar Neutron Probe Experiment. By use of the latest GCR spectra based on BESS measurements and well-benchmarked nuclear interaction models, our calculations well reproduced the data within the experimental error of 15% (measurement) + 30% (systematic) at the region shallower than 300 g/cm2. However, our calculation showed 10-20% higher values in the deeper region.