Attenuation characteristics of MagnaDense high-density concrete at 6, 10 and 15 mv for use in radiotherapy bunker design.

The attenuation characteristics of MagnaDense high-density concrete are measured using the x-ray beams from two Varian linear accelerators at nominal 6, 10, and 15 megavolt energies. The tenth value layers for the primary beam are evaluated under broad- and narrow-beam conditions. The attenuation of secondary radiation is also investigated. Measured data are compared with existing data used in radiotherapy bunker design, derived from the scaling of published tenth value layers for ordinary concrete according to physical density. Instantaneous dose rates around an existing bunker with MagnaDense concrete walls and a conventional concrete roof are predicted using the various different data and compared to actual dose-rate measurements. Primary beam tenth value layer values derived from the broad-beam measurements are found to represent the attenuation properties of the MagnaDense more accurately than those produced by density-based scaling or from narrow-beam measurements.