Supernova neutrino nucleosynthesis of the radioactive Nb observed in primitive meteorites

Hayakawa, Takehito; Nakamura, Ko*; Kajino, Toshitaka*; Chiba, Satoshi; Iwamoto, Nobuyuki  ; Cheoun, M. K.*; Mathews, G. J.*

Short-lived radioactivities are used as nuclearcosmochronometers for understanding the free decay time from the last nucleosynthesis episode until the time of solar system formation (SSF). Nb (half-life of 34.7 Myr) is one of a short-lived isotope existed at SSF. However, there is a controversy in that the inferred initial abundance ratios for Nb/Nb at the time of SSF cluster around two different values; one is near 10, while the other is near 10. Moreover, the astrophysical mechanism for the synthesis of Nb has remained an unsolved problem. Here we argue that conventional nucleosynthesis mechanisms cannot produce Nb and propose a new mechanism for the nucleosynthesis of this isotopebased upon neutrino induced reactions occurring during core-collapse supernova explosions.