S-process isotope abundance anomalies in meteoritic silicon carbide: Data for Dysprosium

Details S-process isotope abundance anomalies in meteoritic silicon carbide: Data for Dysprosium S-process isotope abundance anomalies in meteoritic silicon carbide: Data for Dysprosium

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29..522r&link_type=abstract

Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 522-523

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3

Abundance, Anomalies, Dysprosium Isotopes, Meteoritic Composition, Murchison Meteorite, Silicon Carbides, Absorption Cross Sections, Astronomical Models, Electron Density (Concentration), Mass Spectroscopy, Radioactive Decay, Temperature Effects

Scientific paper

Several trace elements contained in Murchison SiC grains have been found to show clearly the isotopic signature of an overabundance of nuclides from the s-process of nucleosynthesis. The s-process isotopic composition of Dy is of interest because it is affected by the branching at Dy-163. This nucleus is terrestrially stable but it becomes unstable at s-process temperatures due to electron-density-dependent bound-state Beta decay into Ho-163. Using assumptions for neutron density and temperature based on analyses of other branchings a measurement of the isotopic composition of s-process Dy may be able to provide constraints on the electron density at the site of the s-process. Both regression lines indicate a mixture of terrestrial Dy and s-Dy, the composition of which must plot to the left of that of sample 5a. Clearly they are not compatible with the experimental data. Extrapolation of our data to the virtual case of Beta(Dy-163/Dy-162) is equivalent to 1000% shows that Dy-164 is to a large extent produced by the detour Beta decay of Dy-163 neutron capture by Ho-163-Beta decay of Ho-164. An estimate of the s-process composition by extrapolation to vanishing abundances of the p-only isotopes Dy-156 and Dy-158 was not possible because of non-identified molecular interferences at these masses. We therefore give the isotopic composition of sample 5a as a limit for the s-process composition of Dy. Using the neutron capture cross sections from Bao et al. and our data for sample 5a as an upper limit to the ratio (Dy-163/Dy-162)s a branching analysis shows that at least 87% of the Dy-163 produced in the s-process makes a bound-state Beta decay into Ho-163.

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