Аннотация:Abstract—The Bonner sphere technique with activation foil made of natural tantalum is used to estimate doses during secondary particle irradiation. The neutron spectrum in the isocenter of a Varian Trilogy medical linear accelerator (linac) is calculated. The average neutron energy and the effective neutron cross section are determined. The f lux of the (γ, n) reaction is calculated using a measured spectrum. The f luxes measured using Bonner spheres with a natural tantalum activation target correspond to the results from similar measurements obtained in other ways.