Science and Education Publishing Biomedicine and Biotechnology 2328-4137 2 4 2014 11 23 Evaluation of the Average Weighting Factor in Thin Layer Irradiation by Bremsstrahlung 80 84 EN A.V. Belousov Physical department, M.V. Lomonosov Moscow State University, Moscow, Russia U.A. Bliznyuk A.P. Chernyaev BB2014243 10.12691/bb-2-4-3 2014 10 04 2014 11 19 2014 11 23 Photon radiation passing through biological tissues induces streams of secondary particles. Photonuclear reactions produce radiation with high linear energy transfer values and, consequently, a high value of radiation weighting factor (wR). When irradiating thin layers, secondary electrons don't have enough time to transfer all of their energy to the matter of the layer, due to their large range. The heavy particles produced in this process transfer their energy to the matter almost at the location of their production. As a result, the secondary heavy particles may greatly contribute in the equivalent dose, despite the low probability of photonuclear reactions. In this article, the average value of wR is assessed for all types of radiation induced by bremsstrahlung when thin layers are irradiated.