Estimation of effective dose using two ICRP criteria, applied to radiation protection of personnel in an unshielded PET cyclotron facility

Abstract

Neutrons have no charge, but ionize indirectly through secondary particles.Neutron radiation is a source of exposure to ionizing radiation for personnel working withcyclotronsthat produce isotopes forpositron emission tomography (PET) radiopharmaceuticals.During production of isotopes in cyclotron in nuclear reactions beside gamma radiation are created also neutrons. The new recommendations of the International Radiological Protection Commission (ICRP) −103 have changed the method of calculating the neutron radiation weighting factor and the tissue weighting factor value that were defined in earlier ICRP recommendations (ICRP, 2007; ICRP, 1991; ICRP, 1996).The aim of this work is to estimate how this change influencesthe calculation of an effective dose in neutron radiation with a complex energy spectrum. This spectrum consists of three regions: a plateau area for thermal neutrons, a peak in the area of fast neutrons with a sharp edge from the high-energy side, and a mild field of decline for intermediate and epithermal neutrons.The application of new recommendations reduces the calculated effective dose by more than 10 mSv. The effect of increasing the effective dose for the maximum fluence area, i.e. energy near 1 MeV,by using a higher value of wR is negligible. The study finds that the new recommendations are less restrictive, and this is of great practical importance becauseno modification to the used shields is required.