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Presolar Diamond in Meteorites

Presolar diamond, the carrier of the isotopically anomalous Xe component Xe-HL, was the first mineral type of presolar dust that was isolated from meteorites. The excesses in the light, p-process only isotopes 124Xe and 126Xe, and in the heavy, r-process only isotopes 134Xe and 136Xe relative to the solar ratios indicate that Xe-HL was produced in supernovae: they are the only stellar source where these two processes are believed to take place. Although these processes occur in supernovae, their physical conditions and timeframes are completely different. Yet the excesses are always correlated in diamond separates from meteorites. Furthermore, the p-process 124Xe/126Xe inferred from Xe-L and the r-process 134Xe/136Xe from Xe-H do not agree with the p-process and r-process ratios derived from the solar system abundance, and the inferred p-process ratio does not agree with those predicted from stellar models. The 'rapid separation scenario', where the separation of Xe and its radiogenic precursors Te and I takes place at the very early stage (7900 sec after the end of the r-process), has been proposed to explain Xe-H. Alternatively, mixing of 20% of material that experienced neutron burst and 80% of solar material can reproduce the pattern of Xe-H, although Xe-L is not accounted for with this scenario.