Assessment of photon and proton-induced activation in particles accelerators.

Nuclear activation affects all operating, future, or dismantled particle accelerators used in various fields, from medical applications to industrial applications. This work is concerned with the study of the radioactivity induced in various materials (Sc, Cu, Tb, Ta, W, Au) irradiated by hard Bremsstrahlung photons from an electron beam and by secondary neutrons induced by a proton beam. In both cases, the primary beam features an 18 MeV kinetic energy. We have performed Monte Carlo simulations with MCNP, GEANT4, FLUKA, and PHITS, coupled with the analytical codes CINDER'90 or FISPACT-II, to estimate the threshold reaction rates and the induced radioactivity in the samples. We compared the simulations with experimental activation measurements performed by high-resolution gamma spectrometry at a decommissioned medical LINAC and around the CYRCé cyclotron. We also used CR-39 solid-state nuclear track detectors to characterize the thermal and fast neutron components of the secondary fields.