Effect of Phantom Geometry on the Conversion Factor from Exposure to Absorbed Dose

Abstract

The conversion factors from exposure to absorbed dose in water phantoms of slab and spherical geometries are deduced from TLD measurements in polymethylmethacrylate phantoms, for photon energies between ~20 keV and 1.25 MeV, and for depths in the phantom ranging from as close to the surface as feasible to ~1.8 g.cm-2. The conversion factors measured in the slab are found to exceed those measured in the sphere by up to ~10% for the shallow dose equivalent and by somewhat less for the deep dose equivalent. The effect is most pronounced for photon energies between 80 and 140 keV. The results are compared with those deduced from calculations and measurements available in the literature.