Cosmic isotopic composition

The composition of the Earth was determined both by the chemical composition of the solar nebula, from which the sun and planets formed, and by the nature of the physical processes that concentrated materials to form planets. The bulk elemental and isotopic composition of the nebula is believed, or usually assumed to be identical to that of the sun. The few exceptions to this include elements and isotopes such as lithium and deuterium that are destroyed in the bulk of the sun s interior by nuclear reactions. The composition of the sun as determined by optical spectroscopy is similar to the majority of stars in our galaxy, and accordingly the relative abundances of the elements in the sun are referred to as "cosmic abundances." Although the cosmic abundance pattern is commonly seen in other stars there are dramatic exceptions, such as stars composed of iron or solid nuclear matter, as in the case with neutron stars. The... 

The most abundant isotope is which constitutes almost 99% of the carbon in nature. About 1% of the carbon atoms are There are, however, small but significant differences in the relative abundance of the carbon isotopes in different carbon reservoirs. The differences in isotopic composition have proven to be an important tool when estimating exchange rates between the reservoirs. Isotopic variations are caused by fractionation processes (discussed below) and, for C, radioactive decay. Formation of takes place only in the upper atmosphere where neutrons generated by cosmic radiation react with nitrogen ... 

For the following we assume that the atmospheric variations in C02 and in its carbon isotopic composition are entirely due to atmospheric system disturbances, such as the input of 14C-free C02 from fossil C02 production, and deviations from the average rate of 14C production by cosmic radiation. The system dynamics, i.e., the exchange coefficients and the eddy diffusivity are kept constant. We approximate the fossil C02 input p(t) by... 

Rauscher T, Heger A, Hoffman RD, Woosley SE (2002) Nucleosynthesis in massive stars with improved nuclear and stellar physics. Astrophys J 576 323-348 Rayet M (1995) The p-process in type II supemovae. Astron Astrophys 298 517-532 Rayet M, Prantzos N, Amould M (1990) The p-process revisited. Astron Astrophys 227 271-281 Reedy RC, Arnold JR, Lai D (1983) Cosmic-ray record in solar system matter. Science 219 127-135 Rehkamper M, Halliday AN (1999) The precise measurement of T1 isotopic compositions by MC-ICPMS application to the analysis of geological materials and meteorites. Geochim Cosmochim Acta 63 935-944... 

The study of galactic cosmic rays is perhaps more an exercise in taste than in visual appreciation. In fact we determine their composition without ever really seeing them. However, they constitute the only sample of matter in our possession that comes from outside the Solar System. The chemical and isotopic composition of this sample is measured using balloon- or satellite-borne particle detectors, since the Earth s atmosphere is fatal to them. When they slam into nuclei in the air, they fragment into tiny particles, thereby losing their original identity. 

The Mn- Cr system can be studied by TIMS, ICPMS, and SIMS techniques. For TIMS and ICPMS work, bulk samples or mineral separates are dissolved and the solutions are passed through ion-exchange columns to produce clean solutions of manganese and chromium. For minerals with high Mn/Cr ratios SIMS can obtain isotopic data while retaining the petrographic context of the measurements. The chromium isotopic compositions may have to be corrected for small additions of chromium from spallation reactions induced by cosmic rays. This is particularly important in iron-rich meteorites. 

Cosmic rays The 6Li/7Li ratio near 0.6 observed in the cosmic rays is much larger than in the solar system because in cosmic rays both isotopes are spallation fragments of carbon and oxygen created by nuclear reactions between the cosmic rays and the interstellar atoms with which they collide. (See Nucleosynthesis origin, Cosmic rays above, and also see 7Li, below). Thus the Li isotope anomaly in the cosmic rays is understood in terms of the nuclear physics that alters the cosmic-ray composition from what it was originally when the cosmic rays began their high-speed journey. The 6Li/ 7Li ratio observed in the cosmic rays does not, therefore, represent the isotopic composition of Li in any bulk sample of stellar or planetary matter. 

Voshage H. and Hintenberger H. (1963) The cosmic-ray exposure ages of iron meteorites as derived from the isotopic composition of potassium and the production rates of cosmogenic nuclides in the past. In Radioactive Dating, International Atomic Energy Agency, Vienna, pp. 367-379. 

Figure 2 A three-isotope diagram illustrating compositional variations in lunar samples and meteorites, as observed in stepwise in vacuo etching and pyrolysis. Since the observed isotopic compositions do not lie on a single straight line, at least three isotopically distinct components must contribute in variable proportions. These data are interpreted as superposition of solar wind (SW), solar energetic particles (SEP), and galactic cosmic ray, i.e., spallation (GCR)...

The correction of observed at the Earth cosmic ray composition for nuclear fragmentation in the interstellar medium makes it possible to determine the initial elemental and isotopic composition of accelerated particles, to clarify the process of cosmic ray acceleration and the nature of cosmic ray sources. 

The isotopic composition of cosmic rays is now measured for all stable isotopes for elements from H through Ni. The isotopic composition of cosmic ray source material is strikingly similar to the composition found in the solar system. Thus, the solar-like mix of isotopes of Fe and Ni suggests that Type II and Type la supernovae contribute to cosmic-ray source material in proportion similar to their contributions to the solar system [22],... 

There is one well-established anomaly in the isotopic composition of galactic cosmic rays, the excess of 22Ne. The ratio 22Ne/20Ne is enhanced by a factor of 4 compared with the solar reference value [23], It can be explained only by the special conditions of nucleosynthesis. The enhancement of neutron rich isotopes would be expected in the highly evolved very massive stars in... 

Wiedenbeck, M.E. et al. (1999). The isotopic composition of iron, cobalt, and nickel in cosmic ray source material11, 26th ICRC, Salt Lake City, 3, 1. 

DuVernois, M.A. et al. (1996). The Isotopic Composition of Galactic Cosmic-Ray Elements from Carbon to Silicon The Combined Release and Radiation Effects Satellite Investigation11, ApJ 466, 457. 

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