Eunja Ha

Neutrino–nucleus reactions via neutral and charged currents by the quasi-particle random phase approximation (QRPA)

We developed the quasi-particle random phase approximation (QRPA) for neutrino reactions on even–even nuclei via neutral current (NC) and charged current (CC). The QRPA has been successfully applied for nuclear β and ββ decays. To describe neutrino–nucleus reactions, general multipole transitions by the weak interaction with finite momentum transfers are calculated for NC and CC reactions with detailed formulas. Since we consider neutron–proton (np) pairing as well as neutron–neutron (nn) and proton–proton (pp) pairing correlations, the nn + pp QRPA and the np QRPA are combined in a framework, which enables us to describe both NC and CC reactions in a consistent way. Numerical results for ν–12C, –56Fe and –56Ni reactions are shown to match with other theoretical calculations and well reproduce available experimental data.

High-lying Gamow-Teller excited states in the deformed nuclei,76Ge,82Se and N = 20 nuclei in the island of inversion by the Deformed QRPA (DQRPA)

With the advent of high analysis technology in detecting the Gamow-Teller (GT) excited states beyond one nucleon emission threshold, the quenching of the GT strength to the Ikeda sum rule (ISR) seems to be recovered by the high-lying (HL) GT states. We address that these HL GT excited states result from the smearing of the Fermi surface by the increase of the chemical potential owing to the deformation within a framework of the deformed quasi-particle random phase approximation (DQRPA). Detailed mechanism leading to the smearing is discussed, and comparisons to the available experimental data on 76Ge,82Se and N = 20 nuclei are shown to explain the strong peaks on the HL GT excited states.

Neutrino-induced reactions and neutrino scattering with nuclei in low and high neutrino energy

We reviewed present status regarding theoretical approaches for neutrino-induced reactions and neutrino scattering. With a short introduction of relevant data, our recent calculations by distorted-wave Born approximation (DWBA) for quasielastic region are presented for MiniBooNE data. We also discussed that one step-process estimated by the DWBA is comparable to the two-step process, which has been usually used in the neutrino-nucleosynthesis. For much higher energy neutrino data, such as NOMAD data, elementary process approach was shown to be useful instead of using complicated nuclear models. But, in the low energy region, detailed nuclear structure model, such as QRPA and shell model, turn out to be inescapable to explain the reaction data.

Charge exchange reactions and applications to astrophysics

Neutrino-induced reactions have been known to play important roles as the neutrino process on the nucleosynthesis in core collapsing supernovae (SNe) explosions because expected neutrino flux and energy are sufficiently high enough to excite many relevant nuclei in spite of small cross sections of the weak interaction. However, we do not have enough data for the neutrino reaction to be exploited in the network calculation. Only a sparse data in the relevant energy range is known, in specific, for 12C. Therefore we have to rely on theoretical estimation of the reaction, which has two different modes, charge current (CC) and neutral current (NC). In particular, CC reactions are closely related to charge exchange reactions (CEXRs) which are feasible in the experiment, such as, (p,n) or (n,p) reactions. These CEXRs are usually dominated by the Gamow-Teller (GT) transition in the lower energy region. In this respect, any theoretical approaches for the neutrino reaction should be investigated for the CEXR becau...

Gamow-Teller Transitions for Neutron-Rich Nuclei in the Superburst by the Deformed Quasi-particle RPA(DQRPA)

We developed the deformed quasi-particle random phase approximation (DQRPA) for the Gamow-Teller (GT) transition for even-even deformed nuclei. We started from the deformed axially symmetric Woods-Saxon potential based on the Nilsson basis, and performed deformed BCS and deformed QRPA. In this work, we used a realistic two-body interaction taken by Brueckner G-matrix based on the Bonn potential. For the application, we calculated the GT transition for the deformed nuclei at the surface of the neutron star, where electron captures are important heat sources for the carbon flash.

Neutrino-Nucleus Reactions for Nucleosynthesis

We calculated neutrino-induced reactions in the energy range below the quasi-elastic region for nuclei of astrophysical importance. Neutrino-induced reactions have been found to be important for nucleosynthesis in core collapsing supernovae because the expected neutrino flux is sufficiently high enough to excite many relevant nuclei in spite of the small cross section of the weak interaction. Our calculation is carried out with the Quasi-particle Random Phase Approximation (QRPA), which has been successfully applied for the nuclear β and double β decay of relevant nuclei. Our QRPA takes neutron-proton as well as neutron-neutron and proton-proton pairing correlations into account. To describe neutrino reactions, general multipole transitions by the weak interaction with finite momentum transfers are calculated for neutral and charged current reactions. Both reactions are described in a theoretical framework. Our results, which are compared with other theoretical calculations, are shown to well reproduce the sparse experimental data, in specific, for 12C and 56Fe targets. Therefore our results for 40Ar, 56Ni, 138La and 180Ta targets could be valuable data for predicting yields of future measurements of neutrino-induced reactions and further applications to the neutrino-process in the nucleosynthesis.

Neutrino‐Induced Reactions for Nucleosynthesis by the Quasi‐particle RPA

We calculated neutrino‐induced reactions in the energy range below the quasi‐elastic region for nuclei of astrophysical importance. Neutrino‐induced reactions have been found to be important for the nucleosynthesis in core collapsing supernovae explosions because expected neutrino flux is sufficiently high enough to excite many relevant nuclei in spite of small cross sections of the weak interaction. Our calculations are carried out with the Quasi‐particle Random Phase Approximation (QRPA), which successfully described the nuclear beta decays of relevant nuclei by taking neutron‐proton pairing as well as neutron‐neutron and proton‐proton pairing correlations into account. To describe neutrino‐nucleus reactions, general multipole transitions by the weak interaction with finite momentum transfers are considered for neutral and charged current reactions. Both reactions are described in a theoretical framework. Our results are shown to well reproduce the sparse experimental data and extended further for neutr...

Origin of 2{sub 1}{sup +} excitation energy dependence on valence nucleon numbers

It has been shown recently that a simple formula in terms of the valence nucleon numbers and the mass number can describe the essential trends of excitation energies of the first 2{sup +} states in even-even nuclei. By evaluating the first order energy shift due to the zero-range residual interaction, we find that the factor which reflects the effective particle number participating in the interaction from the Fermi orbit governs the main dependence of the first 2{sup +} excitation energy on the valence nucleon numbers.