PRESOLAR GRAINS FROM NOVAE: EVIDENCE FROM NEON AND HELIUM ISOTOPES IN COMET DUST COLLECTIONS

Comets are primitive, kilometer-sized bodies that formed in the outer regions of the solar system. Composed of ice and dust, comets are generally believed to be relic building blocks of the outer solar system that have been preserved at cryogenic temperatures since the formation of the Sun and planets. The analysis of cometary material is particularly important because the properties of cometary material provide direct information on the processes and environments that formed and influenced solid matter both in the early solar system and in the interstellar environments that preceded it.The first direct analyses of proven comet dust were made during the Soviet and European spacecraft encounters with Comet Halley in 1986. These missions carried time-of-flight mass spectrometers that measured mass spectra of individual micron and smaller particles. The Halley measurements were semi-quantitative but they showed that comet dust is a complex fine-grained mixture of silicates and organic material. A full understanding of comet dust will require detailed morphological, mineralogical, elemental and isotopic analysis at the finest possible scale. Electron microscopy and related microbeam techniques will play key roles in the analysis. The present and future of electron microscopy of comet samples involves laboratory study of micrometeorites collected in the stratosphere, in-situ SEM analysis of particles collected at a comet and laboratory study of samples collected from a comet and returned to the Earth for detailed study.

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Path-integral calculation of the fourth virial coefficient of helium isotopes

The Journal of Chemical Physics ◽

10.1063/5.0043446 ◽

2021 ◽

Vol 154 (10) ◽

pp. 104107

Author(s):

Giovanni Garberoglio ◽

Allan H. Harvey

Keyword(s):

Path Integral ◽

Virial Coefficient ◽

Helium Isotopes

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Helium Isotopes Quantum Sieving through Graphtriyne Membranes

Nanomaterials ◽

10.3390/nano11010073 ◽

2020 ◽

Vol 11 (1) ◽

pp. 73

Author(s):

Marta I. Hernández ◽

Massimiliano Bartolomei ◽

José Campos-Martínez

Keyword(s):

Low Temperatures ◽

Quantum Tunneling ◽

Transition State Theory ◽

Selective Adsorption ◽

State Theory ◽

Helium Isotopes ◽

Quantum Calculations ◽

Approximate Methods ◽

Helium Atoms ◽

Quantum Behavior

We report accurate quantum calculations of the sieving of Helium atoms by two-dimensional (2D) graphtriyne layers with a new interaction potential. Thermal rate constants and permeances in an ample temperature range are computed and compared for both Helium isotopes. With a pore larger than graphdiyne, the most common member of the γ-graphyne family, it could be expected that the appearance of quantum effects were more limited. We find, however, a strong quantum behavior that can be attributed to the presence of selective adsorption resonances, with a pronounced effect in the low temperature regime. This effect leads to the appearance of some selectivity at very low temperatures and the possibility for the heavier isotope to cross the membrane more efficiently than the lighter, contrarily to what happened with graphdiyne membranes, where the sieving at low energy is predominantly ruled by quantum tunneling. The use of more approximate methods could be not advisable in these situations and prototypical transition state theory treatments might lead to large errors.

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