The Influence of Radiation Defects in Meteoritic Nanodiamond on the Elemental Composition of the P3 Noble Gas Component

Abstract

Radiation defects in meteoritic nanodiamond produced during noble gas implantation have been ignored so far. At the same time, since the density of the defects depends on the mass of implanted ions with the same energy, graphitization of diamonds with a high density of defects during their thermal metamorphism could be an additional cause of the elemental fractionation of noble gases in the nanodiamond remaining after metamorphism. It has been shown that this factor allows one to explain the variations observed in the elemental composition of one of the main components (P3) of noble gases in the nanodiamond of meteorites thermally metamorphosed to a variable degree. It is also supposed that the bimodal release of the P3 noble-gas component upon pyrolysis of the nanodiamond can be caused by a different density of the radiation defects produced in the crystal lattice of nanodiamond grains during noble gas implantation. In this case, a low-temperature peak of gas release results from the destruction of the grains with a defect density higher than the critical one, at which diamond graphitization occurs at a relatively low pyrolysis temperature, while a high-temperature peak of release arises from the destruction of the nanodiamond grains, where the radiation defects have a weak influence on their graphitization temperature.