Simulation of Primary Radiation Damage in Nickel

The process of radiation damage formation in collision cascades initiated by primary knock-on atoms (PKAs) with energy E_PKA = 5, 10, 15, and 20 keV in nickel at temperatures T = 100, 300, 600, 900, and 1200 K was studied using the molecular dynamics method. To ensure the statistical validity of the results, a series of 24 cascades was modeled for each pair of (E_PKA, T) parameters. The simulation results were analyzed to determine the number N_FP of Frenkel pairs, fractions of vacancies σ_vac and interstitial atoms σ_SIA in clusters of point defects, average sizes of vacancy 〈N_vac〉 and interstitial 〈N_SIA〉 clusters, and average numbers of vacancy 〈Y_vac〉 and interstitial 〈Y_SIA〉 clusters produced in collision cascades as functions of the PKA energy and simulation temperature. It was found that the relation 〈N_FP〉 = 2 ± 0.9 × \(E_{\text{PKA}}^{{1.1 \pm 0.1}}\) holds true at all the examined values of (E_PKA, T). The functional dependences of 〈σ_vac〉 and 〈σ_SIA〉 on E_PKA were identical. The dependence of 〈σ_vac〉 follows that of 〈Y_vac〉, while 〈σ_SIA〉 is governed by 〈N_SIA〉 and the mobility of interstitials. The value of 〈N_vac〉 depends on the irradiation temperature and the thermal stability of vacancy clusters. These clusters are stable at T ≤ 300 K, and 〈N_vac〉 ∝ E_PKA; at 600 ≤ T ≤ 900 K, 〈N_vac〉 ≈ 6 and 10, which corresponds to the sizes of regular stacking fault tetrahedra. The value of 〈Y_SIA〉 is proportional to 〈N_FP〉 and, consequently, to E_PKA in the entire range of PKA energies.