Neutron fluences and doses behind shielded environments in space

Transport code calculations with the code PHITS have been performed to determine the nature of the secondary neutron field produced by galactic cosmic ray (GCR) interactions in aluminum and water shielding. The neutron production from each elemental component of the GCR spectrum was calculated separately, and the total neutron spectrum from the entire incident GCR field was determined from the weighted sum of the individual GCR components. Analysis was then performed on those results to determine the relative importance of specific ranges of neutrons energies in regards to the total neutron fluence and total neutron effective dose. Results indicate that high energy neutrons (above 20 MeV) contribute a significant fraction to both fluence and effective dose. Thus, any new detectors or methodologies being developed for the purpose of neutron detection or neutron dosimetry in space must develop a reliable means of accounting for neutrons above 20 MeV.