Mapeamento do fluxo e estimativa do termo fonte de radiação de campos neutrônicos gerados pelo cíclotron GE PETtrace-8

Abstract

The use of spectrometric techniques in a cyclotron facility is strongly advised for the complete characterization of the neutron radiation field. In recent years, several studies of neutron spectrometry have been carried out at the Cyclotron of the Development Center of Nuclear Technology (CDTN). The main objective of this work is to propose a methodology for mapping of the flux and estimate of the radiation source term of neutron fields generated by the GE PETtrace-8 cyclotron. The method of neutron activation analysis with gold, indium and nickel activation foils was used to measure the activities induced at specific points in the cyclotron bunker. The irradiations of the activation foils were performed using the intermittent irradiation method to optimize the radiation field during 18F production. The study of the neutron spectrum was performed using three radiation source terms. The first source term was constructed based on data provided by the cyclotron manufacturer using the neutron cross sections of the ENDF/B-VII library. The other two were proposed considering the irradiation process used in the routine of 18F production. Both radiation source terms used the LA150H proton cross sections and for the 18O, the cross sections of the physical model CEM03 (Cascade-exciton model) and TENDL (TALYS-based Evaluated Nuclear Data Library) were used. The results of the source terms in relation to the experimental results, in terms of neutron fluence rates, reaction rates and dose equivalent rates, showed that are in the same order of magnitude as those obtained by Ogata et al, Fujibuchi et al, and Gallerani et al., for the same cyclotron; and by Mendez et al. for a different manufacturing cyclotron. The models of the proposed radiation source terms were validated to obtain the spectra generated during the 18F production when water enriched at 18O is bombarded with a proton beam of 16.5 MeV. Finally, the model of the LA150H - TENDL - 2015 radiation source term is closest to the experimental results. This radiation source term can be used for the study in the development of new dosimeters, improved shielding and in the support of future decommissioning studies, concerning PET cyclotrons producing 18F by 18O(p,n)18F nuclear reactions, for the case of proton beams with energies up to 16.5 MeV.