Neutron and capture gamma along the mazes of linear accelerator vaults

Neutron and photon dose equivalents at various points along the mazes of the vaults for two 15 MV linear accelerators were measured. The measurements were made with the machines set at various gantry angles with and without the scattering phantom, and with the collimators set at the maximum and the minimum field sizes. Neutron dose equivalent measurements were made for five other accelerator vaults. Empirical equations were used to fit the dose data at points along the center of the maze, at 1 m above floor level, with the primary radiation beam pointing downward. It is reported here that both the capture gamma and the neutron dose attenuations along the maze are in agreement with the literature. The neutron dose is dependent on the square root of the ratio of the cross-sectional areas of the inner maze entrance and the maze. The tenth value distance (T(N)) is proportional to the square root of the cross-sectional area of the maze.