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TY - UNPB AU - Zheltonozhskaya, M.V. ED - Kuzin, Maksim ED - Schaa, Volker RW TI - The Unwanted Neutrons in Radiation Therapy During the Medical Electron Accelerator Operation J2 - Proc. of RuPAC2018, Protvino, Russia, 1-5 October 2018 C1 - Protvino, Russia T2 - Russian Particle Accelerator Conference T3 - 26 LA - english AB - During radiotherapy using bremsstrahlung gamma quanta with energies greater than 8 MeV, nuclear reactions with neutron emission take place on the brake target and structural materials of a linear accelerator. Because of the high radiobiological danger of neutron radiation, especially fast neutrons, their contribution to the total beam flux substantially increases the dose received by the patient. We conducted studies of the braking gamma quanta and neutrons flows directly at the place of the patient's treatment at a distance of 1 m from the virtual source of gamma quanta with a radiation field size of 20x20 cm². The use of direct spectrometric methods for measuring the flux of gamma quanta and neutrons in this case is extremely difficult due to the high flux density (according to some estimates ~10¹² particles*cm⁻²*s). Therefore, for solving this problem, we used the photoactivation method. Registration of gamma quanta and neutrons was carried out using (gamma, n) and (n, gamma)-reactions. The natural tantalum 181Ta as one of the most studied nuclei in both photonuclear reactions and in reactions with neutrons in a wide energy range, was used as a detecting target. For the experiment, two Varian Trilogy medical accelerators with different operating life were used: accelerator 1 with long operating life (boundary energy 18 MeV) accelerator 2 with short operating life (boundary energy 20 MeV). PB - JACoW CP - Geneva, Switzerland ER -