PNNL

Abstract

Displacement cascades are simulated by molecular dynamics (MD) methods in alpha-Fe containing different concentrations of substitutional He atoms. Primary knock-on atom (PKA) energies, Ep , from 500 eV to 5 keV are considered at the irradiation temperature of 100 K. The concentration of He in Fe varies from 1% to 5%, and the results are compared with simulations performed in pure alpha-Fe. We find that the average number of Frenkel pairs per cascade (NF) at low concentrations of He atoms is nearly the same as that in pure Fe, but NF increases with increasing He concentration. The present studies demonstrate for the first time that small He-vacancy bubbles can be nucleated directly from displacement cascades, even for low temperatures at which the vacancies are not mobile. Furthermore, the production efficiency of He-vacancy clusters increases with increasing He concentration and PKA energy. The mechanisms of He bubble nucleation in displacement cascades are discussed in detail.