Simulation of neutron-induced damage in tungsten by irradiation with energetic self-ions

A direct comparison of the deuterium (D) decoration of radiation-induced damage in polycrystalline tungsten irradiated with self-ions [present work] and neutrons in the high-flux isotope reactor (HFIR) (Hatano et al., 2013) shows a reasonably good agreement at least up to 0.3 displacement per atom indicating that MeV heavy ions can be a good proxy to simulate neutron-produced damage at room temperature and low dpa. The coefficient of similarity between two kinds of irradiation was obtained experimentally to be K_exp ∼ 0.65 ± 0.1 in the case of the deuterium decoration of both kinds of radiation-induced defects with low and high de-trapping energies for deuterium. We introduced the theoretical estimation for coefficient of similarity between neutron- and self-ion-irradiations, which is a fraction of common area under the curves of two overlapping damage energy spectra of primary knock-on atom (PKA) produced in tungsten by these two types of irradiation. In other words, K_sim is a part of displaced atoms produced in the similar conditions under two different types of irradiation. The theoretical values of K_sim = 0.34 and K_sim = 0.29 were obtained for tungsten target irradiated with 20 MeV self-ions in comparison to irradiation with neutrons in HFIR reactor (>0.1 MeV) and 14 MeV neutrons, respectively. The theoretical value of K_sim = 0.34 is about two times less than the experimental value of K_exp = 0.65. It means that high energy PKAs can play more important role in the production of similar damage structure by irradiation with self-ions and neutrons which is responsible for deuterium retention. The model assuming that all cascades with an energy higher than T_c = 150 keV split into identical sub-cascades gives the value of K_sim = 0.64 ± 0.01 for the coefficient of similarity between HFIR-neutron and 20 MeV self-ion irradiations that is in an agreement with experimental value of K_exp = 0.65 ± 0.1. Consequently, splitting of high-energy part of cascades might take place in W that results in a reduction of the effective PKA spectrum and a change of types and density of post-radiation defects