The absorbed dose in the vicinity of an interface between two media irradiated by a 60Co source

Monte Carlo techniques are used to generate the distribution of absorbed dose in the vicinity of an interface between two media. Computer-generated distributions for absorbers comprising the media carbon-copper, water-aluminium and aluminium-water are presented. The features of the distributions in regions of electron equilibrium and non-equilibrium, in particular finite discontinuities at the boundaries and subsequent build up or build down, are discussed both qualitatively and quantitatively. The difficulties inherent in interpreting ionization measurements in the neighbourhood of interfaces are outlined.