Comparing the effects of various (p,xn) radionuclide production routes on induced radioactivity in the concrete walls of a cyclotron vault.

This article focuses on the neutron-induced long-lived radioactivity in concrete walls of cyclotron vaults used for medical isotope production in Taiwan. It systematically compares the activation effects of secondary neutrons generated from eleven (p,xn) nuclear reactions involving nine target materials across thirteen cyclotrons, highlighting that non-self-shielded cyclotrons can cause significant concrete activation. Using FLUKA Monte Carlo simulations, the study evaluates neutron fluxes and induced radionuclide activities, particularly of ^54Mn, ^60Co, and ^152Eu, and demonstrates that adding a neutron-absorbing layer (polyethylene and boron carbide) to concrete surfaces effectively reduces induced radioactivity, especially from thermal neutrons. The findings provide a broader understanding of concrete activation beyond the commonly studied ^18O(p,n)^18F reaction, offering practical insights for managing radioactive waste and shielding design in medical cyclotron facilities.