Neutron production from 100 and 230 AMeV He interactions in water, PMMA and iron

Neutrons produced by galactic cosmic ray (GCR) interactions in spacecraft and habitat materials can comprise a significant fraction of the effective dose received by humans in thickly shielded environments in space. Calculations done by the University of Tennessee group indicate that cosmic ray He interactions in both thin and thick shields can produce up to 30% of the total neutron fluence. However, little information is available on neutron production by medium-energy He particles, especially in the critical 100 to 2000 AMeV range of He energies. Here we have measured neutron yields from 100 and 230 AMeV He stopping in water, iron, and PMMA targets. Water and PMMA both have excellent GCR shielding properties due to their hydrogen content. Iron is a common elemental component of Martian regolith, and is also part of some man-made structures in space. Measurements were conducted at the HIMAC facility at the National Institute of Radiological Sciences in Chiba, Japan. Neutrons were measured at laboratory angles between 0 and 120 degrees in the laboratory, and were measured at neutron energies above 2 MeV. Experimental results will be presented, along with FLUKA and MCNP transport model simulations of the experiments.