  Neutrons are encountered in many different fields, including condensed matter
physics, space exploration, nuclear power, and healthcare. Neutrons interacting
with a biological target produce secondary charged particles that are damaging
to human health. The most effective way to shield neutrons is to slow them to
thermal energies and then capture the thermalized neutrons. These factors lead
us to consider potential materials solutions for neutron shields that maximize
the protection of humans while minimizing the shield mass, and which adapt well
to modern additive manufacturing techniques. Using hexagonal boron nitride
(hBN) as a capture medium and high-density polyethylene (HDPE) as a
thermalization medium, we aim to design the optimal internal structure of
h$^{10}$BN/HDPE composites by minimizing the effective dose, which is a measure
of the estimated radiation damage exposure for a human. Through Monte Carlo
simulations in Geant4, we find that the optimal structure reduces the effective
dose up to a factor of 72x over aluminum (Al) and 4x over HDPE; this is a
significant improvement in shielding effectiveness that could dramatically
reduce the radiation exposure of occupational workers.
