Abundances of La138 and Ta180 Through ν-Nucleosynthesis in 20M ⊙ Type II Supernova Progenitor, Guided by Stellar Models for Seeds

Abstract

Yields of nature’s rarest isotopes La138 and Ta180 are calculated by neutrino processes in the Ne-shell of density ρ ≈ 104 g/cc in a type II supernova (SN II) progenitor of mass 20 M ⊙. Two extended sets of neutrino temperature - T ν e = 3, 4, 5, 6 MeV and T ν(μ/τ)= 4, 6, 8, 10, 12 MeV respectively for charged and neutral current processes are taken. Solar mass fractions of the seeds La 139, Ta 181, Ba 138 and Hf 180 are taken for calculation. They are assumed to be produced in some s-processing events of earlier generation massive ‘seed stars’ with average interior density range 〈ρ〉≈103−106 g/cc. The abundances of these two elements are calculated relative to O 16 and are found to be sensitive to the neutrino temperature. For neutral current processes with the neutron emission branching ratio, b n = 3.81 × 10−4 and b n = 9.61 × 10−1, the relative abundances of La138 lie in the ranges 4.48 × 10−14−2.94 × 10−13 and 1.13 × 10−10−7.43 × 10−10 respectively. Similarly, the relative abundances of Ta180 lie in the ranges 1.80 × 10−15−1.17 × 10−14 and 4.53 × 10−12−2.96 × 10−11 respectively for the lower and higher values of the neutron emission branching ratio. For charged current processes, the relative abundances of La138 and Ta180 are found to be in the ranges 1.38 × 10−9−7.62 × 10−9 and 2.09 × 10−11−1.10 × 10−10 respectively. Parametrized by density of the ‘seed stars’, the yields are found to be consistent with recent supernova simulation results throughout the range of neutrino temperatures. La138 and Ta180 are found to be efficiently produced in charged current interaction.