Measured neutron beam line shielding effectiveness of several iron/polyethylene configurations

Neutron and gamma-ray leakage measurements were taken at various stages of shield construction for neutron flight path 5 (the Lash-up flight path) at LANSCE, to compare the relative effectiveness of several configurations. Dose equivalent rates were determined for three categories: low-energy neutrons, below 20 MeV; high-energy neutrons, above 20 MeV; and gamma rays, as measured by hand-held survey instruments. The low-energy neutrons were measured by activation of an indium foil in a paraffin-filled cadmium cannister, sized to be generally insensitive above 20 MeV. High-energy neutrons were measured by (n,2n) production of Carbon 11 in a plastic scintillator with a 20-MeV threshold. Thermal neutrons were not measured at the shield-leakage test points. Room-scattered neutrons were observed by Albatross IV detector readings, which were taken beside the shield as a measure of variation of room background as the shield configuration changed. 1 fig., 1 tab