Validation of Monte Carlo simulations by experimental measurements of neutron-induced activation in cyclotrons

Abstract

Nuclear activation is the process of production of radionuclides by irradiation. This phenomenon concerns particle accelerators used in various fields, from medical applications to industrial ones, both during operation and at the decommissioning phase. For more than three decades, the possibility of using cyclotrons for nuclear power generation and nuclear waste reduction has also been discussed, i.e. in the case of Accelerator-Driven Systems [1]. The radioprotection and dismantling issues of accelerator facilities, that have been raised recently, is even more potent for such installations. In our study, we are particularly interested in the activation due to secondary neutrons produced by (x,n) reactions, mostly (p,n) occurring in the accelerator’s components. This work focuses on the study of the radioactivity induced in various materials (V, Sc, Tb, W, Ta) irradiated by fast and thermal neutrons, in two different scenarios: through direct irradiation -with an AmBe sourceand around an operating cyclotron at the CYRCé facility (Strasbourg). A broad Monte Carlo study including FLUKA, GEANT4, PHITS and MCNP simulation has been performed, with and without a FISPACT-II coupling, to estimate the reaction rates and to trace the induced radioactivity in samples of known composition. The results of the simulations are compared with the values extracted in two dedicated experimental campaigns in which activated samples underwent high resolution gamma-ray spectrometry.