The potential primary component composition of xenon in nanodiamond-enriched fractions (NDFs) of meteorites was determined under the assumption that it contains two almost normal, but different isotopic components (Xe-P3 and Xe-P3n). The Xe-P3n component is contained in the individual population of diamond grains, while the Xe-P3 component is contained in diamond-like rims on the diamond grains. The presence of the Xe-P3n component made it possible to use radioactive products of the classical r-process of nucleosynthesis during a type II supernova explosion to form, according to the hypothesis of Ott (1996), two xenon components with an anomalous isotopic composition (Xe-pr1n and Xe-pr2n) without an increased isotope content of 132Xe relative to the isotope content of 136Xe. It is assumed that the implantation (sorption) of isotopes of the Xe-pr1n and Xe-pr2n components into their carrier phases probably occurred in turbulent mixing zones of different compositions in the outer and inner shells of a type II supernova after its explosion. The Xe-pr1n component is contained in an individual population of nanodiamond grains, while the Xe-pr2n carrier phase is first suggested to be SiC-X grains, the evolution of which is associated with a type II supernova. Therefore, when SiC-X grains are destroyed, for example, under laboratory conditions, a mixture of Xe-S and Xe-pr2n components is released, which we denote as Xe-X. Thus, according to the concept we proposed, the primary component composition of xenon consists, in addition to Xe-S, of Xe-P3, Xe-P3n, Xe-pr1n and Xe-X, contained in different individual carrier phases. Successful calculations of the abundances of these components in the NDF of such different meteorites as Murchison CM2 and Allende CV3 and their analysis have shown that the above components may be real components.

Анализ кинетики выделения C, N и Xe из промежуточной по размерам зерен фракции наноалмаза метеорита Orgueil (CI) при впервые проведенном изотермическом пиролизе и последующем окислении показал следующее: (а) при постоянной температуре пиролиза скорость выделения углерода, также как азота и ксенона, уменьшается со временем; (б) относительное количество выделенного ксенона, в основном нормального по изотопному составу (Хе-Р3), при разной продолжительности пиролиза до 800°С определяется, главным образом, температурой нагрева, тогда как азота – как температурой, так и продолжительностью нагрева; (в) продолжительный пиролиз приводит к существенному изменению распределения в зернах алмаза нормального ( 15N = 0) и аномального ( 15N = –350 ) по изотопному составу азота. Выявленные особенности кинетики выделения углерода и азота объяснены на основании различной энергии связи хемосорбированного кислорода с поверхностными атомами углерода и нахождения основной доли азота в протяженных дефектах кристаллической решетки наноалмаза. Основными факторами уменьшения скорости выделения Хе-Р3 при изотермическом пиролизе наноалмаза являются либо различие графитоподобных фаз-носителей Хе-Р3 по величинам параметров десорбции ксенона из ловушек в этих фазах, либо различная степень радиационной дефектности зерен популяции, содержащей имплантированный Хе-Р3. Сделаны выводы, что (1) в наноалмазе метеоритов фаза-носитель инертных газов Р3 компоненты, независимо от ее природы, по относительному содержанию углерода является незначительной и (2) процесс образования популяции зерен наноалмаза, содержащих основное количество аномального по изотопному составу азота, протекал с высокой скоростью, что обеспечило его сохранность, главным образом, в протяженных дефектах кристаллической решетки алмаза.

Introduction: The nature of the planetary noble gas carrier (Q) in meteorites remains uncertain. It is known that it is likely to be carbonaceous, but represents only a small fraction of the total macromolecular material. Q is oxidisible with nitric and other oxidizing acids. It seems to be partly destroyed with pyridine and may have an organic structure. Previously, we have shown that during parent body thermal metamorphism Q is less affected than the majority of other carbonaceous materials. If organic matter is graphitized, as has happened in the enstatite chondrite parent bodies, Q remains unaffected. In the present study we have found that Q is also separable from the majority of carbon in type 2 and 3 CR chondrites during stepped combustion. It is possible that this is because Q has become encased within the matrix, in contrast to other carbon phases, during parent body metamorphism.

We hypothesize the formation of neon associated with isotopically anomalous xenon (Xe-HL) in meteoritic nanodiamonds and designated as Ne-X through the mixing of the Ne-HL and Ne-S subcomponents. The Ne-HL subcomponent is neon from the helium (He/C) zone of a type II supernova or a mixture of neon from this zone and its hydrogen zone, while the Ne-S subcomponent is spallation neon formed during a supernova explosion in nuclear spallation reactions induced by high-energy protons. Based on this hypothesis and the presumed abundances of neon isotopes in the zones of a high-mass (25 M ⊙ ) supernova after its explosion, we have calculated the abundances of neon components in nanodiamond separates and its grain-size fractions. Our calculations have shown the following. (1) The main source of Ne-HL is neon from the helium zone of the supernova; as a result, the 20 Ne/ 22 Ne and 21 Ne/ 22 Ne ratios for Ne-X are 0.26 ± 0.03 and 0.19 ± 0.04, respectively. The isotopic composition of Ne-X is identical to that for Ne-A2 if Ne-HL is produced by the mixing of neon from the helium and hydrogen zones in proportion 1: 1.06. (2) In meteoritic nanodiamonds, the main neon abundance is determined by neon of the P3 component (Ne-P3). Ne-P3 is retained during thermal metamorphism, because it is sited in traps of the crystal lattice of diamond with a high energy of its activation. (3) The Ne-X/Ne-P3 ratio increases with nanodiamond grain size; as a result, there is no need to invoke an additional neon component (Ne-P6) to interpret the data on neon in meteoritic nanodiamonds.

Based on an analysis of possible distributions of xenon, nitrogen, and carbon components between two populations of diamond grains from the Orgueil CI and Allende CV3 meteorites, the following conclusions were drawn concerning the properties of nanodiamond grain populations in the meteorites. (1) The isotopically anomalous HL component of noble gases, at least Xe-HL, and the major portion of nitrogen consisting of an isotopically light component (delta(15)N = -350parts per thousand) occur in different nanodiamond grain populations (referred to as populations HL and N, respectively). The abundance of population HL grains is at least 14 wt % for the diamond of Orcueil CI and increases by a factor of almost 1.5 in the diamond of the thermally metamorphosed carbonaceous chondrite Allende CV3. (2) The diamond grains of population HL have a protosolar origin, whereas population N grains provide no compelling evidence for such an origin. Compared with population N grains, the nucleation and initial growth of population HL grains occurred from heavy-isotope enriched carbon. The grains of population N began growing from carbon with a delta(13)C value of about -43.7parts per thousand, whereas this value ranged from about -7 to similar to-32parts per thousand in population HL grains. In addition, the gas medium of population HL formation was either nitrogen-free, or nitrogen entrapment by the growing diamond was inhibited. (3) Diamond grains of both populations contain equal amounts of surface-bound nitrogen, whose delta(15)N is constrained from about 0 to similar to18000parts per thousand depending on the astrophysical source of this nitrogen. Nitrogen with delta(15)N similar to 0 is probably most plausible. Such nitrogen could be chemisorbed and (or) adsorbed from the terrestrial atmosphere by diamond grains during their separation from meteorite material. (4) During thermal metamorphism, population HL grains were destroyed to a lesser extent compared with population N grains. For instance, during the metamorphism of the Allende material, the mass fraction of population HL grains decreased by a factor of 2.1 +/- 0.4, whereas that of population N decreased by a factor of no less than 3.3 +/- 0.5. A possible explanation for the better preservation of population HL grains compared with population N is the relatively high defect density in the lattice of the latter produced by atoms of volume-bound nitrogen.

Presolar diamond recovered from the Boriskino CM2 meteorite was separated into size fractions by sedimentation in an ultracentrifuge. The average grain sizes of the fractions ranged from similar to1.4 to similar to5.3 nm. Noble gases were measured in each diamond fraction and in the bulk sample in the course of stepped pyrolysis up to 700degreesC and subsequent oxidation between 600 and 900degreesC. The following main results were obtained: (a) fine diamond fractions are strongly different from coarse ones in the elemental composition of the P3 component of noble gases, which is most likely related to element fractionation during implantation into diamond grains; (b) in presolar diamond from a single meteorite, a wide range of the Xe-P3/Xe-HL ratio was detected for the first time, from 0.13 +/- 0.06 for the fine fraction to 3.95 +/- 0.37 for the coarse fraction, which is suggestive of different energies of ions of the P3 and HL noble gas components during their implantation into diamond grains; (c) the calculated upper Xe-136/Xe-132 for isotopically anomalous xenon (0.71 +/- 0.04) in the fine fraction is identical to a value of 0.7 determined by Hass and Lewis (1994) for Xe-LH in diamond from thermally metamorphosed meteorites. Such a coincidence suggests that Xe-HL was formed as an individual component before its implantation into the grains of presolar diamond as a result of mixing of the products of the r- and p-processes of nucleosynthesis during a supernova explosion with xenon of the isotopically normal component of noble gases. The elemental composition of the latter component is significantly different from that of the P3 component, at least with respect to Ar-36/Xe-132.

The diamond obtained from the Novo-Urei meteorite by acid leaching was examined using a combination of X-ray diffractometry (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The micromorphology, orientation of the crystal structure relative to crystal faces (crystallometry of developed crystal surfaces), and other structural features of the diamond particles suggest that they have been formed by means of martensite transformation of:graphite crystals under the effect of shock metamorphism. The fact that impact diamonds from the Novo-Urei meteorite belong to a single phase and have little defects points to their origin in the region of high impact pressures and residual temperatures, i.e., as a result of a large-scale impact event.

Amounts and isotopic compositions of C, N, and noble gases were measured in the same gas portions extracted by step heating (over the temperature interval of 300–2000°C) of two different-size fractions of interstellar diamond from the Efremovka CV3 chondrite. The analysis of these data and their comparison with the data obtained for the same fractions during their oxidation and with results of the pyrolysis of whole-rock diamond samples from other chondrites led us to conclude that (1) the fine-grained diamond is more heat-resistant than the coarse-grained diamond, perhaps, because of an increase in the percentage of defect grains and the concentrations of defects in them with an increase in the grain size; (2) graphitization and oxidation of nanometer-sized diamond grains result in an uniform (for example, layer by layer) mechanism of destruction; (3) N, He, and, to a lesser degree, Ne release during pyrolysis proceeds predominantly by means of diffusion, whereas Ar and Xe are liberated mostly during grain destruction; (4) coarse-grained diamond is enriched in associations of two and more N atoms, which can be released at lower temperatures than those of single N atoms; and (5) an increase in the thermal-metamorphism grade of the parental material of chondrites leads to a more rapid destruction of coarse-grained diamond than its fine-grained analogue. For example, the material of the Indarch chondrite, which was affected by the most intense thermal metamorphism among all chondrites considered, contains mainly fine-grained interstellar diamond.

The Open University's repository of research publications and other research outputs C, N and noble gases in different pH and grain size fractions of pre-solar diamonds from Boriskino chondrite Conference Item and noble gases in different pH and grain size fractions of pre-solar diamonds from Boriskino chondrite.

Concentrations anti isotopic compositions of carbon, nitrogen, and noble gases were determined in interstellar diamond separated from the CR and CI carbonaceous components of the Kaidun meteoritic breccia. The diamonds in the CR and CI components were found to be very similar and resemble diamonds in the Orgueil CI and Murchison CM2 chondrites. These facts indicate a homogeneous mixing of interstellar diamond grains of different populations in the protoplanetary nebula, including in the area of formation of parent bodies for CR meteorites. It is shown that the carbonaceous matter of the Kaidun meteorite suffered heterogeneous heating. i.e., some portions of the meteorite did not experience long-term heating above 100 degreesC, which resulted in preservation of all noble gas components in the diamond grains.