Secondary shielding barriers for diagnostic x-ray facilities: scatter and leakage revisited.

Methods are presented for determining the thickness requirements for barriers against scatter and leakage radiation generated in a diagnostic x-ray facility. Equations are developed that express the shielded doses due to scatter and leakage with explicit dependence on the operating potential used in clinical settings. The 1972 scatter experiment of Trout and Kelley is revisited, with suggested values for the scatter fraction that are somewhat different from those used in Report Number 49 of the NCRP. The dose from leakage radiation due to operation at clinical kVp settings is seen to be orders of magnitude below that predicted by the model in NCRP49. The unshielded secondary radiation dose in air at unit distance and workload is presented as a function of operating potential and for clinical workload distributions. The net transmission of secondary radiations through common shielding materials is presented. Compared to that for the primary beam at the same potential, the transmission of secondary radiation is more penetrating due to the inclusion of leakage radiation that has been hardened by the tube housing. Sample shielding calculations illustrate the utility of this scheme.