arXiv subjects

Eunja Ha

Publications and source records attributed to Eunja Ha.

33 records · Page 2Linked to original sources

arXiv2020

Deformed relativistic Hartree-Bogoliubov theory in continuum with point coupling functional: examples of even-even Nd isotopes

The aim of this work is to develop the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) theory based on the point-coupling density functionals and extend it to provide a unified description for all even-even nuclei in the nuclear chart by overcoming all possible challenges. The nuclear superfluidity is considered via Bogoliubov transformation. Densities and potentials are expanded in terms of Legendre polynomials to include the axial deformation degrees of freedom. Sophisticated relativistic Hartree-Bogoliubov equations in coordinate space are solved in the DiracWoods-Saxon basis to consider the continuum effects. Numerical checks are performed from light nuclei to heavy nuclei. The techniques to construct the DRHBc mass table for even-even nuclei are explored. The DRHBc theory is extended to study heavier nuclei beyond magnesium isotopes. Taking Nd isotopes as examples, the experimental binding energies, two-neutron separation energies, quadrupole deformations, and charge radii are reproduced rather well. The deformation and continuum play essential roles in the description of nuclear masses and prediction of drip-line nuclei. By examining the single-particle levels in the canonical basis and their contributions to the total density, the thickness of the neutron skin, the particles number in continuum, and the Coulomb barrier, the exotic structures including the neutron skin and the proton radioactivity are predicted.

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arXiv2019

Neutrino self-interaction and MSW effects on the supernova neutrino-process

We calculate the abundances of $^{7}$Li, $^{11}$B, $^{92}$Nb, $^{98}$Tc, $^{138}$La, and $^{180}$Ta produced by neutrino $(ν)$ induced reactions in a core-collapse supernova explosion. We consider the modification by $ν$ self-interaction ($ν$-SI) near the neutrinosphere and the Mikheyev-Smirnov-Wolfenstein effect in outer layers for time-dependent neutrino energy spectra. Abundances of $^{7}$Li and heavy isotopes $^{92}$Nb, $^{98}$Tc and $^{138}$La are reduced by a factor of 1.5-2.0 by the $ν$-SI. In contrast, $^{11}$B is relatively insensitive to the $ν$-SI. We find that the abundance ratio of heavy to light nucleus, $^{138}$La/$^{11}$B, is sensitive to the neutrino mass hierarchy, and the normal mass hierarchy is more likely to be consistent with the solar abundances.

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arXiv2018

Competition of deformation and neutron-proton pairing in Gamow-Teller transitions for $^{56, 58}$Ni and $^{62,64}$Ni

We investigated effects of neutron-proton ($np$) pairing correlations comprising isoscalar (IS) and isovector (IV) component on Gamow-Teller (GT) transitions of $^{56, 58,62,64}$Ni by taking into account nuclear deformation in a deformed Woods-Saxon mean field. Our GT calculations based on a deformed Bardeen-Cooper-Schriffer (DBCS) approach have been performed within a deformed quasi-particle random phase approximation (DQRPA) which explicitly includes the deformation as well as all kinds of pairing correlations not only at the DBCS but also at the DQRPA stage. Competition of these two effects, the deformation and the IS spin-triplet and IV spin-singlet component of the $np$ pairing, is shown to be significant for understanding the GT strength distributions of Ni isotopes.

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arXiv2014

Gamow-Teller Strength distributions in $^{76}\textrm{Ge}$, $^{76,82}\textrm{Se}$, and $^{90,92}\textrm{Zr}$ by the Deformed Proton-neutron QRPA

We developed the deformed proton-neutron quasiparticle random phase approximation (QRPA) and applied to the evaluation of the Gamow-Teller (GT) transition strength distributions including high-lying excited states, which data becomes recently available beyond one or two nucleon threshold by charge exchange reactions using hundreds of MeV projectiles. Our calculations started with single-particle states calculated by a deformed axially symmetric Woods-Saxon potential. Neutron-neutron and proton-proton pairing correlations are explicitly taken into account at the deformed Bardeen Cooper Schriffer theory. Ground state correlations, and two-particle and two-hole mixing states are included in the deformed QRPA. In this work, we use a realistic two-body interaction given by the Brueckner $G$-matrix based on the CD Bonn potential to reduce the ambiguity on the nucleon-nucleon interactions inside nuclei. We applied our formalism to the GT transition strengths for $^{76}$Ge, $^{76,82}$Se, and $^{90,92}\textrm{Zr}$, and compared to available experimental data. The GT strength distributions were sensitive on the deformation parameter as well as its sign, {\it i.e.}, oblate or prolate. The Ikeda sum rule, which is usually thought to be satisfied under the one-body current approximation irrespective of nucleon models, is used to test our numerical calculations and shown to be satisfied without introducing the quenching factor, if high-lying GT excited states are properly taken into account. Most of the GT strength distributions of the nuclei considered in this work turn out to have the high-lying GT excited states beyond one nucleon threshold, which are shown to be consistent with available experimental data.

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arXiv2013

Shell evolution of N=20 nuclei and Gamow-Teller strengths of $^{30,32,34}$Mg by the deformed QRPA

Gamow-Teller (GT) strength distributions of Mg isotopes are investigated within a framework of the deformed quasi-particle random phase approximation(DQRPA). We found that the N=20 shell closure in $^{28 \sim 34}$Mg was broken by the prolate shape deformation originating from the {\it fp}-intruder states. The shell closure breaking gives rise to a shift of low-lying GT excited states into high-lying states. Discussions regarding the shell evolution trend of single particle states around N=20 nuclei are also presented with the comparison to other approaches.

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arXiv2013

High-lying Gamow-Teller excited states in the deformed nuclei, $^{76}\textrm{Ge}$ and $^{82}\textrm{Se}$, by the smearing of the Fermi surface in Deformed Quasi-particle RPA (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 seems to be recovered by the high-lying GT states. Moreover, in some nuclei, the stronger GT peaks than any other peaks appear explicitly in the high-lying excited states. We address that these high-lying GT excited states stems 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 are shown to explain the strong peaks on the high-lying GT excited states in a satisfactory manner.

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arXiv2011

Roles of High-lying Excited States on Neutrino Reactions and the Gamow Teller strength for $^{40}$Ar

Neutrino reactions on $^{40}$Ar via charged and neutral currents for detecting solar and core collapsing supernovae (SNe) neutrinos and the Gamow Teller strength are calculated by considering the high-lying excited states up to a few tens of MeV region. The nucleus was originally exploited to identify the solar neutrino emitted from $^{8}$B produced in the pp-chains on the Sun. With the higher energy neutrinos emitted from the core collapsing SNe, contributions from higher multi-pole transitions including the spin dipole resonances (SDR) as well as the Gamow Teller (GT) and Fermi transitions are shown to be important ingredients for understanding reactions induced by the SNe as well as solar neutrinos. In this work, we focused on the role of high-lying excited states which are located beyond a few low-lying states known in the experiment. Expected large difference between the cross sections of $ν_e$ and ${\bar ν_e}$ reactions on $^{40}$Ar, which difference has been anticipated in previous calculations because of the large Q value in the ${\bar ν}_e$ reaction, is significantly diminished. The reduction leads only to about 2 times difference between them. Our calculations are carried out by the Quasi-particle Random Phase Approximation (QRPA), which takes account of the neutron-proton pairing as well as proton-proton and neutron-neutron pairing correlations. They were successfully applied in the description of the nuclear beta decay and relevant neutrino reaction data on $^{12}$C and $^{56}$Fe, and the GT data on the $^{138}$La and $^{180}$Ta.

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arXiv2011

Neutrino induced reactions related to the $ν$-process nucleosynthesis of ${}^{92}$Nb and ${}^{98}$Tc

It has recently been proposed that ${}^{92}_{41}$Nb and ${}^{98}_{43}$Tc may have been formed in the $ν$-process. We investigate the neutrino induced reactions related to the $ν$-process origin of the two odd-odd nuclei. The main neutrino reactions for ${}^{92}_{41}$Nb are the charged-current (CC) $^{92}$Zr($ν_e,e^{-}$)$^{92}$Nb and the neutral-current (NC) $^{93}$Nb($ν ({\bar ν}), ν^{'} ({\bar ν})^{'}$ n)$^{92}$Nb reactions. The main reactions for ${}^{98}_{43}$Tc, are the CC reaction $^{98}$Mo($ν_e,e^-$)$^{98}$Tc and the NC reaction $^{99}$Ru($ν ({\bar ν}), ν^{'} ({\bar ν})^{'}$ p)$^{98}$Tc. Our calculations are carried out using the quasi-particle random phase approximation. Numerical results are presented for the energy and temperature dependent cross sections. Since charge exchange reactions by neutrons may also lead to the formation of ${}^{92}_{41}$Nb and ${}^{98}_{43}$Tc, we discuss the feasibility of the $^{92}$Mo(n,p)$^{92}$Nb and $^{98}$Ru(n,p)$^{98}$Tc reactions to produce these nuclei.

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arXiv2010

Neutrino reactions via neutral and charged current by Quasi-particle Random Phase Approximation(QRPA)

We developed the quasi-particle random phase approximation (QRPA) for the neutrino scattering off even-even nuclei via neutral current (NC) and charged cur- rent (CC). The QRPA has been successfully applied for the βand ββdecay of relevant nuclei. To describe neutrino scattering, general multipole transitions by weak interactions with a finite momentum transfer are calculated for NC and CC reaction with detailed formalism. Since we consider neutron-proton (np) pairing as well as neutron-neutron (nn) and proton-proton (pp) pairing correlations, the nn + pp QRPA and np QRPA are combined in a framework, which enables to describe both NC and CC reactions in a consistent way. Numerical results for ν-^{12}C, -^{56}Fe and -^{56}Ni reactions are shown to comply with other theoretical calculations and reproduce well available experimental data.

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arXiv2010

Neutrino reactions on $^{138}$La and $^{180}$Ta via charged and neutral currents by the Quasi-particle Random Phase Approximation (QRPA)

Cosmological origins of the two heaviest odd-odd nuclei, $^{138}$La and $^{180}$Ta, are believed to be closely related to the neutrino-process. We investigate in detail neutrino-induced reactions on the nuclei. Charged current (CC) reactions, $^{138}$Ba$ (ν_e, e^{-}) ^{138}$La and $^{180}$Hf$ (ν_e, e^{-}) ^{180}$Ta, are calculated by the standard Quasi-particle Random Phase Approximation (QRPA) with neutron-proton pairing as well as neutron-neutron, proton-proton pairing correlations. For neutral current (NC) reactions, $^{139}$La$ (ν ν^{'}) ^{139}${La}$^*$ and $^{181}$Ta$ (ν, ν^{'}) ^{181}$Ta$^*$, we generate ground and excited states of odd-even target nuclei, $^{139}$La and $^{181}$Ta, by operating one quasi-particle to even-even nuclei, $^{138}$Ba and $^{180}$Hf, which are assumed as the BCS ground state. Numerical results for CC reactions are shown to be consistent with recent semi-empirical data deduced from the Gamow-Teller strength distributions measured in the ($^{3}$He, t) reaction. Results for NC reactions are estimated to be smaller by a factor about 4 $\sim$ 5 rather than those by CC reactions. Finally, cross sections weighted by the incident neutrino flux in the core collapsing supernova are presented for further applications to the network calculations for relevant nuclear abundances.

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arXiv2009

Rotational energy term in the empirical formula for the yrast energies in even-even nuclei

We show that part of the empirical formula describing the gross features of the measured yrast energies of the natural parity even multipole states for even-even nuclei can be related to the rotational energy of nuclei. When the first term of the empirical formula, $αA^{-γ}$, is regarded as the otational energy, we can better understand the results of the previous analyses of the excitation energies. We show that the values of the parameters $α$ and $γ$ newly obtained by considering the $αA^{-γ}$ term as the rotational energy of a rigid rotor are remarkably consistent with those values extracted from the earlier `modified' $χ^2$ analyses, in which we use the logarithms of the excitation energies in defining the `modified' $χ^2$ values.

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arXiv2007

Universal Expression for the Lowest Excitation Energy of Natural Parity Even Multipole States

We present a new expression for the energy of the lowest collective states in even-even nuclei throughout the entire periodic table. Our empirical formula is extremely valid and holds universally for all of the natural parity even multipole states. This formula depends only on the mass number and the valence nucleon numbers with six parameters. These parameters are determined easily and unambiguously from the data for each multipole state. We discuss the validity of our empirical formula by comparing our results with those of other studies and also by estimating the average and the dispersion of the logarithmic errors of the calculated excitation energies with respect to the measured ones.

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arXiv2007

N_p N_n Scheme Based on New Empirical Formula for Excitation Energy

We examine the $N_p N_n$ scheme based on a recently proposed simple empirical formula which is highly valid for the excitation energy of the first excited natural parity even multipole states in even-even nuclei. We demonstrate explicitly that the $N_p N_n$ scheme for the excitation energy emerges from the separate exponential dependence of the excitation energy on the valence nucleon numbers $N_p$ and $N_n$ together with the fact that only a limited set of numbers is allowed for the $N_p$ and $N_n$ of the existing nuclei.

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arXiv2007

Origin of $2_1^+$ 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 $2^+$ 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 $2^+$ excitation energy on the valence nucleon numbers.

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arXiv2007

Empirical formula for the excitation energies of the first $2^+$ and $3^-$ states in even-even nuclei

We report empirical findings that a simple formula in terms of the mass number $A$, the valence proton number $N_p$, and the valence neutron number $N_n$ can describe the essential trends of excitation energies $E_x$ of the first $2^+$ and $3^-$ states in even-even nuclei throughout the periodic table. The formula reads as $E_x = αA^{-β} + \exp (- λN_p) + \exp (- λN_n)$. The parameter $β$ in the first term is determined by the mass number $A$ dependence of the bottom contour line of the excitation energy systematics. The other two parameters $α$ and $λ$ are fitted by minimizing the $χ^2$ value between the measured and calculated excitation energies. Our results suggest that the single large-$j$ shell simulation can be applied to the excitation energies of the first $2^+$ and $3^-$ states in even-even nuclei.

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