  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.
