Supernova neutrino nucleosynthesis of the radioactive ⁹²Nb observed in primitive meteorites

The isotope ⁹²Nb decays to ⁹²Zr with a half-life of 3.47 × 10⁷ yr. Although this isotope does not exist in the current solar system, initial abundance ratios for ⁹²Nb/ ⁹³Nb at the time of solar system formation have been measured in primitive meteorites. The astrophysical origin of this material, however, has remained unknown. In this Letter, we present new calculations which demonstrate a novel origin for ⁹²Nb via neutrino-induced reactions in core-collapse supernovae (ν-process). Our calculated result shows that the observed ratio of ⁹²Nb/⁹³Nb ∼ 10^-5 can be explained by the ν-process.