The effect of neutron-moderating materials in high-energy linear accelerator mazes

A study was undertaken to examine the effect of lining high-energy linear accelerator mazes with neutron-moderating materials in order to reduce scattered neutron dose at the accelerator room door. Polyethylene alone reduced neutron dose by no more than 27% and did not significantly reduce gamma ray dose. Polyethylene combined with flexboron panels reduced neutron dose by 50% at most, reducing gamma ray dose by a maximum of 32%. Much greater reductions in both neutron and gamma ray dose (by 92% and 55% respectively) can be obtained by incorporating polyethylene and boron into either internal or external maze doors. Our results support the conclusion that neutrons directly incident on the maze from the accelerator contribute little to the neutron dose at the door, and that the majority of neutron dose is due to scattered and thermal neutrons.