Analysis of Neutron Effects for Asteroid Disruption

The use of nuclear weapons is one possible method for disrupting or deflecting an asteroid on a trajectory to impact the earth. A largely unexplored component of weapon yield in a disruption scenario is the impact of the neutron output. The results of MCNP-6 simulations are presented demonstrating the effect that incident neutron energy has on the total energy deposited in an asteroid, including that the efficiency of energy deposition in a material is inversely proportional to the incident neutron energy due to negative Q-value reactions. The effects of material composition on the total energy deposited as well as the spacial distribution are also explored. The neutron energy deposition profilesles are further assessed using the hydrodynamics code Spheral, to evaluate the effect of varying energy deposition proles on disruption effectiveness. In most materials, an increase in neutron energy results in an increase in per-neutron energy deposition. In meteoric iron, however, an increase in incident neutron energy above 12 MeV results in lower per-neutron energy deposition due to a sharp rise in the occurrence of the (n,2n) reaction in some of the isotopic constituents. This suggests that isotopic composition, and not just elemental composition, could influence the energy deposition due to the neutron yield of a nuclear weapon. Neutron yield coupling efficiency and disruption efficiency for 14.1 MeV neutrons is significantly lower than for 2.45 MeV neutrons or a thermonuclear neutron spectrum