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RESEARCH PRODUCT

Interpretation of the Solar 48Ca/46Ca Abundance Ratio and the Correlated Ca-Ti-Cr Isotopic Anomalies in Inclusions of the Allende Meteorite

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In the past, astrophysical models encountered severe difficulties in explaining the solar 46,48Ca abundances or the correlated Ca-Ti-Cr isotopic anomalies observed in inclusions of the Allende meteorite [1–3]. Among the various attempts. SANDLER et al. [4] suggested the production of neutron-rich stable Ca-Ti-Cr isotopes in a high neutron density environment of ~107 mol/cm3 with a neutron-exposure time of 10 s. Assuming the initial abundances to be solar and applying Hauser-Feshbach neutron-capture crosa sections, the above authors have calculated a 48Ca/46Ca abundance ratio which is only a factor of 2.6 smaller than the observed solar value of 56. However, the predicted isotopic anomalies for Ca and Ti were too large by factors of 13 and 5, respectively, compared to those in the EK-1–4-1 inclusion of the Allende meteorite [1,2]. Recently KAPPELER et al. [5] have estimated the steady-state abundance ratio of 46,48Ca in a high neutron-density environment, but could not reproduce the solar-system value. In a different approach, HARTMANN et al. [6] have calculated the composition of matter that has gone through a phase of nuclear statistical equilibrium in the deep interior of a supernova and is ejected with large neutron excess. With this model it is possible to fit the solar 46Ca/46Ca ratio and also the Ti-Cr abundances in the inclusion Gl [3], but the Ca-Ti correlation [1.2] is not well reproduced. Additional difficulties arise from the fact that also other neutron-rich isotopes are overproduced by large factors.