Molybdenum and Zirconium Isotopes from a Supernova Neutron Burst

We analyze the nucleosynthesis implications of the recent discovery by M. J. Pellin and collaborators that two odd isotopes of molybdenum, 95 Mo and 97 Mo, are overabundant in type X SiC grains: X grains condensed within expanding supernova interiors. We find that a rapid release of neutrons (on a timescale of seconds) with fluence τ = 0.07-0.08 neutrons mbarn -1 produces the observed pattern by way of abundant production of progenitor radioactive Zr isotopes. This suggests that the condensing matter was in a supernova shell in which rapid burning was occurring at the time of ejection, probably owing to the passage of the shock wave from the core. Which shell, and the exact source of the neutrons, is still unknown, but we present a model based on the shock of an He shell.