Molecular dynamics approach for predicting release temperatures of noble gases in pre-solar nanodiamonds

Abstract

Pre-solar meteoritic nanodiamond grains carry an array of isotropically anomalous noble gas isotopes and provide information on the history of nucleosynthesis, galactic mixing and the formation of the solar system. In this paper, we develop a molecular dynamics approach to predict thermal release distribution of implanted noble gases (He and Xe) in nanodiamonds. Our simulations show that low-energy ion-implantation is a viable way for the incorporation of noble gases into nanodiamonds. Accordingly, we provide atomistic details of the unimodal temperature release distribution for helium and a bimodal behavior for xenon. Intriguingly, our model shows that the thermal release process of noble gases is highly sensitive to the impact and annealing parameters as well as to crystallographic orientation. In addition, the model elegantly explains the unimodal and bimodal behaviour via the interstitial and substutional types of defects formed. In particularly, our approach explains the origin of the famous Xe-P3 and Xe-HL peaks, and shows that P3 component in meteoritic literature releases not only at the low-temperature but also at the high-temperature along with HL component. This means that an isotopically anomalous HL component must be the sum of high temperature part of P3 component and a pure-HL component.