Results 251 to 260 of about 60,044 (291)

Stable isotope abundances in calcretes

Geological Society, London, Special Publications, 1983
Summary About 300 published and unpublished measurements of carbon and oxygen stable isotope ratios of calcretes are compared in an attempt to define general trends. The δ 13 C values of the carbonates range from − 12 to + 4‰ PDB. On a global scale the main factor responsible for the average 13
A. S. Talma, F. Netterberg
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Isotopic magnesium abundances in stars

Monthly Notices of the Royal Astronomical Society, 1988
Les spectres a haute resolution du systeme MgH A-X pres de 5130 A fournissent les rapports d'abondance isotopique de 25 Mg/ 24 Mg et 26 Mg/ 24 Mg, pour un echantillon d'etoiles incluant plusieurs etoiles naines et geantes du vieux disque, une etoile baryum classique et une mixte, et une geante faible de la bande ...
A. McWilliam, D. L. Lambert
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Carbon Isotope Abundance in Meteoritic Carbonates

Science, 1963
The C 13 /C 12 ratio in the carbonate minerals of Orgueil, a carbonaceous chondrite, is 6 percent greater than the ratio in any known terrestrial carbon. The effect may be produced by a chemical isotope fractionation involving processes not common on earth, or it may be the result of ...
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Interpretation of Lead Isotope Abundances

Nature, 1962
I SHOULD like to make further comment about two points which have arisen in the correspondence from Aswathanarayana1,2 and Russell and Slawson3. The first is to support the observations of the latter authors about the importance of proper allowance for mass-spectrometric tail effects.
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Lithium Isotopic Abundances in Stars

2008
The Li isotope ratio, 6Li/7Li, in stars can be determined from the isotopic shift in the Li I 670.8 nm resonance line. Because of the small effect this however requires truly precision spectroscopy: spectral resolving power R ≥ 105 and S/N ≥ 500. In this review we discuss the method and what one can learn from Li isotopic abundances in terms of Big ...
Poul Erik Nissen, Martin Asplund
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Elemental Composition Determinations Using the Abundant Isotope

Journal of the American Society for Mass Spectrometry, 2019
Elemental compositions are commonly determined from the exact m/z of the monoisotopic peak, which is often the lightest isotope. However, the lightest isotope peak is often weak or absent and the monoisotopic peak can be difficult to identify for organometallics, polyhalogenated compounds, or large molecules.
Robert B, Cody, Thierry, Fouquet
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Isotopic Abundances in RGB- and AGB-Stars

2006
Asymptotic Giant Branch stars contribute significantly to the chemical evolution of their host galaxies. All stars with a main-sequence mass = 8M ? will return eventually 30-80% of their mass to the interstellar medium. In parallel to the He-burning phase, which follows the original main sequence H-burning, AGB stars are known to produce heavy elements.
Käufl, Hans Ulrich, Aringer, Bernhard, Uttenthaler, Stefan, Hron, Josef   +3 more
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Isotopic Abundance Variations in Meteorites

Science, 1963
H C, Urey, V R, Murthy
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Isotopic abundance challenge

Analytical and Bioanalytical Chemistry, 2008
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Isotopic Abundances in Interstellar Clouds

1977
The observation of microwave spectra of molecules in interstellar clouds allows separation and detection of the lines of isotopes of many of the more common elements. Comparison of intensities of isotopic lines shows that the relative isotopic abundances for C, O, S, N, and Si are generally rather similar to those found on Earth.
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