Investigation on the contribution of secondary particles to an absorbed dose for local irradiation by 200-MeV protons

The contribution of secondary particles to an absorbed dose for a narrow 200-MeV proton beam has been investigated on the medico-biological proton beam of the ITEP synchrotron. The authors consider the contribution of secondary particles generated in the inner-nuclear cascade as well as particles formed in the process of decay of excited nuclei. Results of measuring dose of secondary radiation by means of nuclear photo-emulsions are presented. It is concluded that the magnitude of the correction in the absorbed dose depends linearly on the size of the beam. When hypophyse is irradiated by a narrow 6-mm diameter beam, this correction amounts to 5.5% of the dose of secondary protons