Neutrino reactions on La138 and Ta180 via charged and neutral currents by the quasiparticle random-phase approximation

The cosmological origins of the two heaviest odd-odd nuclei La138 and Ta180 are believed to be closely related to the neutrino process. We investigate in detail neutrino-induced reactions on the nuclei. Charged current (CC) reactions Ba138(νe,e^-)La138 and Hf180(νe,e^-)Ta180 are calculated using the standard quasi-particle random phase approximation (QRPA) with neutron-proton pairing as well as neutron-neutron and proton-proton pairing correlations. For the neutral current (NC) reactions La139(ν, ν^′)La139^* and Ta181(ν, ν^′)Ta181^*, we generate ground and excited states of the odd-even target nuclei La139 and Ta181 by operating one quasiparticle to even-even nuclei Ba138 and Hf180, which are assumed as the BCS ground state. Numerical results for CC reactions are shown to be consistent with recent semiempirical data deduced from the Gamow-Teller strength distributions measured in the (He3,t) reaction. Results for NC reactions are estimated to be about 4 to 5 times smaller than the results for CC reactions. Finally, cross sections weighted by the incident neutrino flux in the core-collapse supernova are presented for further applications to the network calculations for relevant nuclear abundances.