Energy spectra of primary knock-on atoms under neutron irradiation

TL;DR

This paper introduces a rigorous methodology for calculating primary knock-on atom spectra under neutron irradiation, providing a detailed understanding of damage mechanisms beyond the traditional dpa measure.

Contribution

It presents a new approach to compute PKA spectra considering various recoiling species and energies, improving damage assessment accuracy in neutron-irradiated materials.

Findings

PKA spectra are complex and species-dependent.

PKA spectra vary with time, neutron field, and material.

Different damage quantification methods yield comparable results.

Abstract

Materials subjected to neutron irradiation will suffer from a build-up of damage caused by the displacement cascades initiated by nuclear reactions. Previously, the main "measure" of this damage accumulation has been through the displacements per atom (dpa) index. There are known limitations associated with the dpa quantity and its domain of application and therefore this paper describes a more rigorous methodology to calculate the primary atomic recoil events (often called the primary knock-on atoms or PKAs) that lead to cascade damage events as a function of energy and recoiling species for any simulated or measured neutron irradiation scenario. Via examples of fusion relevant materials, it is shown that the PKA spectra can be complex, involving many different recoiling species, potentially differing in both proton and neutron number from the original target nuclei, including high energy recoils of light emitted particles such as alpha-particles and protons. The variations in PKA spectra as a function of time, neutron field, and material are explored. Example PKA spectra are applied to radiation damage quantification using the binary collision approximation and stochastic cluster dynamics, and the results from these different approaches are discussed and compared.