This study is devoted to the investigation of the interaction of photon radiation with an energy of up to 30 MeV with thin layers, which simulates the conditions of radiobiological experiments on determination of the relative biological efficiency (RBE). The values of the absorbed dose of all of the produced particles in irradiated layers were determined via computer simulation using Geant4 and the equivalent dose was calculated. Computer experiments were performed in media of different elemental compositions: water and model biological tissue. We demonstrate that starting from the threshold of photonuclear reactions on light elements the equivalent dose of monochromatic radiation differs from the absorbed dose by a factor of 3‒15 depending on the layer thickness and composition. Similar calculations for bremsstrahlung spectra also demonstrate a noticeable difference between the absorbed and equivalent doses in a layer.
Department of Physics, Moscow State University, Moscow, 119991 Russia