Neutrino reactions on 138La and 180Ta via charged and neutral currents by the quasiparticle random-phase approximation

The cosmological origins of the two heaviest odd-odd nuclei La-138 and Ta-180 are believed to be closely related to the neutrino process. We investigate in detail neutrino-induced reactions on the nuclei. Charged current (CC) reactions Ba-138(v(e),e(-))La-138 and Hf-180(v(e),e(-))Ta-180 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 La-139(v,v ')La-139* and Ta-181(v,v ')Ta-181*, we generate ground and excited states of the odd-even target nuclei 139La and 181Ta by operating one quasiparticle to even-even nuclei 138Ba and 180Hf,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 (He-3,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.