title: C, N, and noble gas isotopes in grain size separates of presolar diamonds from Efremovka.
abstract: Nanometer-size presolar diamonds from the Efremovka CV3 chondrite were physically separated into several grain size fractions by ultracentrifugation. The coarsest size fraction is the most enriched in carbon-12; the others have broadly similar carbon isotopic compositions. Measurement of noble gases shows that their concentration decreases with decreasing grain size. This effect is attributed to ion implantation. Such an episode could occur in the envelope of a supernova that produced the diamonds, or in interstellar space; in either case, ions with energies above a certain threshold pass completely through the smaller diamond grains without being captured. Concentrations of nitrogen show only minor variations with grain size, indicating a different mechanism of incorporation into the diamonds.
authors.affiliation: Planetary Sciences Research Institute, Open University, Walton Hall, Milton Keynes, UK.
authors.forename: A B
authors.initials: AB
authors.lastname: Verchovsky
authors.forename: A V
authors.initials: AV
authors.lastname: Fisenko
authors.forename: L F
authors.initials: LF
authors.lastname: Semjonova
authors.forename: I P
authors.initials: IP
authors.lastname: Wright
authors.forename: M R
authors.initials: MR
authors.lastname: Lee
authors.forename: C T
authors.initials: CT
authors.lastname: Pillinger
mesh_terms: D002244:Carbon / Q000032:analysis*; D018130:Diamond; D007554:Isotopes; D019110:Meteoroids; D009584:Nitrogen / Q000032:analysis*; D005741:Noble Gases / Q000032:analysis*
chemical_list: D007554:Isotopes; D005741:Noble Gases; D002244:Carbon; D018130:Diamond; D009584:Nitrogen