Shielding materials for high-energy neutrons

The authors used the Monte Carlo transport code Los Alamos High-Energy Transport (LAHET) to study the shielding effectiveness of common shielding materials for high-energy neutrons. The source neutron spectrum was from the interaction of an 800-MeV proton beam and iron target. In a normal incident, the neutrons collided with walls made of six common shielding materials: water, concrete, iron, lead, polyethylene, and soil. The walls were of four different thicknesses: 25, 50, 75 and 100 cm. They then tallied the neutron spectra on the other side of the shielding wall and calculated the neutron doses. For the high-Z materials--iron and lead--they find that many neutrons with energies between 1--10 MeV are created when high-energy neutrons interact with shielding materials. For materials containing low-Z elements--water, soil, concrete, and polyethylene--the spectra show higher energy peaks at about 100 MeV. The studies show that for a given wall thickness, concrete is more effective than the other materials. They also studied the effectiveness of combinations of materials, such as concrete and water, concrete and soil, iron and polyethylene, or iron polyethylene and concrete