Effects of Channeling on Damage Production in Iron

The displacement efficiency $K\left(E\right)\mathrm{}$ for damage production by energetic iron atoms in $\alpha$ iron was computed by simulating complete elastic collision cascades in a bcc atomic array on a high-speed computer. Energies in the range $0.1<~E<~30$ keV were considered. Above 1 keV, $K\left(E\right)\mathrm{}$ decreased monotonically as a consequence of progressively more frequent knock-on channeling. Relative to their values in the low-energy, nonchanneling range, the energy-dependent displacement efficiency given by this study and that given by Sigmund's theory are in agreement. Our extrapolated $K\left(E\right)\mathrm{}$ value at 50 keV was 0.6 that at 1 keV. Damage production by primary knock-ons, per se, was attenuated by quasichanneling. Pure channeling was observed only for higher order knock-ons. In the case of reactor irradiation, the computed $K\left(E\right)\mathrm{}$ leads to an over-all damage reduction of 35% relative to that predicted by simple cascade theory. This indicates that the ignoration of channeling effects (crystal structure) in simple cascade theory is not totally responsible for its overestimation of damage production by at least a factor of 2.