Activation products in a treatment room of a 15 MV linear accelerator for medical use

Linacs working above 8 MV produce an undesirable neutron field mainly through (γ, n) nuclear reactions. Due to room-return effect inside the vault there is a thermal neutron flux that is constant regarded the distance to the isocenter. When thermal neutrons collide with the bunker walls and the Linac head some radioisotopes are induced in the concrete, wedges and collimators due to neutron and photon activation. The aim of this work is to study the induced radioisotopes in concrete samples and a wedge, which emits gamma-ray during its decay, the presence of this protons will represent a radiological risk for the patient. Induced radioisotopes were studied with a 15 MV Linac, and a gamma-ray spectrometer with a Nal(Tl) scintillator where 846.8, 1368.6 and 1778.8 keV gamma-rays were observed, these photons are produced during the decay of 54Mn, 24Na and 28Al respectively, being in agreement with radionuclides reported in the literature. (Author)