Secondary neutron emissions and induced activity quantification during 14 MeV proton irradiation of thick natural...

Present work provides a comprehensive insight of the secondary neutron environment as well as the production of medically significant radioisotopes, ⁸⁹Zr, ⁸⁸Zr and ⁸⁸Y during proton irradiation of natural yttrium target. The emission neutron energy spectra, ambient dose equivalents and the fluence rate at different directions with respect to the incident proton beam were estimated using the Monte Carlo simulations. The estimated quantities were validated using calibrated dosimetric instruments. Based on the neutron dosimetric estimates, possible neutron induced activations in the structural and shielding materials are expected and selection of raw materials with low induced activity potential is strongly recommended during design of accelerator based ⁸⁹Zr production facilities. The ⁸⁹Zr yield estimation and possible production pathways for ⁸⁸Zr and ⁸⁸Y were also investigated. The effect of Fe impurity in the yttrium target and quantification of induced cobalt (⁵⁶Co and ⁵⁸Co) isotopes were performed. These cobalt impurities can contribute significantly if the bio-kinetic removal is slow; hence minimization of the Fe-impurity concentration in yttrium target is crucial in medical radioisotope production facilities. During this study, the ⁸⁹Zr production through neutron absorption of ⁸⁸Zr could not be observed due to lower neutron fluence around the target and possible proton irradiation experiments of prolonged duration with high proton current may be emphasized in future.