Neutrino-Induced Nucleosynthesis in Helium Shells of Early Core-Collapse Supernovae

We summarize our studies on neutrino-driven nucleosynthesis in He shells of early core-collapse supernovae with metallicities of Z ≤ 10^-3 Z_Ȯ. We find that for progenitors of ∼ 11-15 M_Ȯ, the neutrons released by ⁴He(ν¯e_e, e⁺n)³H in He shells can be captured to produce nuclei with mass numbers up to A ∼ 200. This mechanism is sensitive to neutrino emission spectra and flavor oscillations. In addition, we find two new primary mechanisms for neutrino-induced production of 9Be in He shells. The first mechanism produces ⁹Be via ⁷Li(n,γ)⁸Li(n,γ)⁹Li(e^- ν¯e_e)⁹Be and relies on a low explosion energy for its survival. The second mechanism operates in progenitors of ∼ 8 M_Ȯ, where ⁹Be can be produced directly via ⁷Li(³H, n₀)⁹Be during the rapid expansion of the shocked Heshell material. The light nuclei ⁷Li and ³H involved in these mechanisms are produced by neutrino interactions with ⁴He. We discuss the implications of neutrino-induced nucleosynthesis in He shells for interpreting the elemental abundances in metal-poor stars.