arXiv subjects

Yoshiko Kanada-En'yo

Publications and source records attributed to Yoshiko Kanada-En'yo.

At least 91 records · Page 5Linked to original sources

arXiv2013

Cluster states and monopole transitions in $^{16}$O

Cluster structures and monopole transitions in positive parity states of $^{16}$O were investigated based on the generator coordinate method calculation of an extended $^{12}$C+$α$ cluster model. The ground and excited states of a $^{12}$C cluster are taken into account by using $^{12}$C wave functions obtained with the method of antisymmetrized molecular dynamics. The $0^+_2$ state of $^{16}$O and its rotational members, the $2^+_1$ and $4^+_1$ states are described well by the cluster states dominated by the $^{12}$C($0^+_1$)+$α$ structure. Above the $^{12}$C($0^+_2$)+$α$ threshold energy, we obtained a $0^+$ state having the $^{12}$C($0^+_2$)+$α$ cluster structure, which is considered to be a candidate for the $4α$ cluster gas state. The band structures were discussed based on the calculated $E2$ transition strength. Isoscalar Monopole excitations from the ground state were also discussed.

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arXiv2013

Dineutron formation and breaking in $^8$He

We discuss the correlation of the spin-singlet two-neutron pair, the dineutron correlation, in the ground and excited $0^+$ states of $^8$He by using a method to describe the dineutron correlation in neutron-rich nuclei, the dineutron condensate wave function. The shell-model configuration and the dineutron configuration compete with each other in the ground state of $^8$He. We compare the ground state structure of $^8$He with that of $^6$He and suggest that the dineutron correlation is weaker in the ground state of $^8$He than $^6$He. We also suggest the possibility of the dineutron condensation in an excited $0^+$ state of $^8$He. In addition, we investigate the formation mechanism of the dineutron condensation in $^8$He by using a newly developed framework, $α$ and dineutron condensate wave function, and conclude that the attraction from the core is essential for the formation of the dineutron condensation.

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arXiv2013

Mesonic and non-mesonic branching ratios of K^- absorption in the nuclear medium

The branching ratios of K^- absorption at rest in nuclear matter are evaluated from the K^- self-energy by using the chiral unitary approach for the s-wave \bar{K} N amplitude. We find that both the mesonic and non-mesonic absorption potentials are dominated by the Λ(1405) contributions. We also observe that the mesonic absorption ratio [π^{-} Σ^{+}] / [π^{+} Σ^{-}] increases as a function of nuclear density due to the interference between Λ(1405) and the I=1 non-resonant background, which is consistent with experimental results. The fraction of the non-mesonic absorption is evaluated to be about 30 % at the saturation density. The branching ratios of the K^- absorption at rest into deuteron and 4He are also calculated.

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arXiv2013

Adiabatic internuclear potentials obtained by energy variation with the internuclear-distance constraint

We propose a method to obtain adiabatic internuclear potentials via energy variation with the intercluster-distance constraint. The adiabatic $^{16}$O + $^{16,18}$O potentials obtained by the proposed method are applied to investigate the effects of valence neutrons in $^{16}$O + $^{18}$O sub-barrier fusions. Sub-barrier fusion cross sections of $^{16}$O + $^{18}$O are enhanced more compared to those of $^{16}$O + $^{16}$O because of distortion of valence neutrons in $^{18}$O.

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arXiv2012

Branching ratios of mesonic and nonmesonic antikaon absorptions in nuclear medium

The branching ratios of K^- absorption at rest in nuclear matter are theoretically investigated in order to understand the mechanism of K^- absorption into nuclei. For this purpose mesonic and nonmesonic absorption potentials are evaluated as functions of nuclear density, the kaon momentum and energy from one- and two-body K^- self-energy, respectively. By using a chiral unitary approach for the s-wave Kbar N amplitude we find that both the mesonic and nonmesonic absorption potentials are dominated by the Lambda(1405) contributions. The fraction of the mesonic and nonmesonic absorptions are evaluated to be respectively about 70% and 30% at the saturation density almost independently on the kaon momentum. We also observe different behavior of the branching ratios to pi ^+ Sigma^- and pi^- Sigma^+ channels in mesonic absorption due to the interference between Lambda(1405) and the I=1 nonresonant background, which is consistent with experimental results. The nonmesonic absorption ratios [Lambda p]/[Sigma^0 p] and [Lambda n]/[Sigma^0 n] are about unity while [Sigma^+ n]/[Sigma^0 p] and [Sigma^- p]/[Sigma^0 n] are about two due to the Lambda(1405) dominance in absorption. Taking into account the kaon momenta and energies, the absorption potentials become weaker due to the downward shift of the initial K^-N two-body energy, but this does not drastirally change the nonmesonic fraction. The Sigma(1385) contribution in the p-wave Kbar N amplitude is examined and found to be very small compared to the Lambda(1405) contribution in slow K^- absorption.

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arXiv2012

alpha-cluster correlations and symmetry breaking in light nuclei

$α$-cluster correlations in the ground states of $^{12}$C and $^{16}$O are studied. Because of the $α$ correlations, the intrinsic states of $^{12}$C and $^{16}$O have triangle and tetrahedral shapes, respectively. The deformations are regarded as spontaneous symmetry breaking of rotational invariance, and the resultant oscillating surface density is associated with a density wave (DW) state caused by the instability of Fermi surface with respect to a kind of $1p$-$1h$ correlations. To discuss the symmetry breaking between uniform density states and the oscillating density state, a schematic model of a few clusters on a Fermi gas core in a one-dimensional finite box was introduced. The model analysis suggests structure transitions from a Fermi gas state to a DW-like state via a BCS-like state, and to a Bose Einstein condensation (BEC)-like state depending on the cluster size relative to the box size. It was found that the oscillating density in the DW-like state originates in Pauli blocking effects.

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arXiv2012

Novel cluster states in $^{10}$Be

Cluster structures of excited $^{10}$Be states are investigated with a hybrid model of dineutron condensate wave functions and $^6$He+$α$ cluster wave functions. Two kinds of cluster states are theoretically suggested a few MeV above the $α+α+n+n$ threshold energy. They have quite distinct cluster structure; ones have gas-like structures of $α+α$+dineutron, and the others have $^6$He+$α$ with extremely extended an $α$ cluster. Although these cluster states have not been confirmed experimentally yet, theoretically suggested properties of these states such as monopole transition strengths and $α$-decay widths may be helpful for possible experimental observation.

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arXiv2012

Separation of a Slater determinant wave function with a neck structure into spatially localized subsystems

A method to separate a Slater determinant wave function with a two-center neck structure into spatially localized subsystems is proposed, and its potential applications are presented. An orthonormal set of spatially localized single-particle wave functions is obtained by diagonalizing the coordinate operator for the major axis of a necked system. Using the localized single-particle wave functions, the wave function of each subsystem is defined. Therefore, defined subsystem wave functions are used to obtain density distributions, mass centers, and energies of subsystems. The present method is applied to separations of Margenau--Brink cluster wave functions of $α+ α$, $^{16}$O + $^{16}$O, and $α+ ^{16}$O into their subsystems, and also to separations of antisymmetrized molecular dynamics wave functions of $^{10}$Be into $α$ + $^6$He subsystems. The method is simple and applicable to the separation of general Slater determinant wave functions that have neck structures into subsystem wave functions.

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arXiv2012

Breaking of N=8 magicity in 13Be

Structure of $^{13}$Be was investigated with antisymmetrized molecular dynamics. The variation after spin and parity projections was performed. An unnatural parity $1/2^-$ state was suggested to be lower than $5/2^+$ state indicating that vanishing of the N=8 magic number occurs in $^{13}$Be. A low-lying $3/2^+$ state with a $2\hbarω$ configuration was also suggested. Developed cluster structures were found in the intruder states. Lowering mechanism of the intruder states was discussed in terms of molecular orbitals around a $2α$ core.

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arXiv2012

Cluster structures in $^{11}$B

Structures of excited states in $^{11}$B are investigated with a method of $β$-$γ$ constraint antisymmetrized molecular dynamics in combination with the generator coordinate method. Various excited states with developed cluster core structures are suggested in positive- and negative-parity states. For negative-parity states, we suggest a band with a $2α+t$ cluster structure. This band starts from the $3/2^{-}_{3}$ state and can correspond to the experimental band observed recently. In positive-parity states, two $α$ core cluster structures with surrounding nucleons are found. A $K^π=1/2^+$ band is suggested to be constructed from a remarkably developed cluster structure with a large prolate deformation. We discuss features of the cluster structure in association with molecular orbital structures of $^{10}$Be.

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arXiv2012

Antisymmetrized molecular dynamics and its applications to cluster phenomena

Structure and reaction studies with a method of antisymmetrized molecular dynamics (AMD) were reviewed. Applications of time-independent and time-dependent versions of the AMD were described. In applications of time-independent AMD to nuclear structure studies, structures of neutron-rich nuclei such as Be, C, Ne, and Mg isotopes were described focusing on cluster aspects. Important roles of valence neutrons were discussed. The results suggested a variety of cluster structures appear also in unstable nuclei as well as in stable nuclei. Deformation and cluster phenomena in $Z\sim N$ nuclei in $p$- and $sd$- shell regions were also discussed. Applications of time-dependent AMD contain various topics such as fragmentation in heavy-ion collisions as well as nuclear responses. The AMD calculations successfully describe multifragmentation which is one of the remarkable phenomena in heavy-ion collisions. The approach is able to link reactions and nuclear matter properties. The studies suggested the important balance between single-particle motions and correlations to form clusters and fragments.

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arXiv2011

$^6$He-triton cluster states in $^9$Li

Cluster states in $^9$Li are investigated with calculations of a $^6$He-$t$ cluster model. Results suggest $^6$He-$t$ cluster states near the $^6$He-$t$ threshold energy. These states construct a $K^π=1/2^-$ band and their neutron configuration is similar to that of the $K^π=0^+_2$ band in $^{10}$Be.

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arXiv2011

Be-$α$ correlations in the linear-chain structure of C isotopes

We investigate the linear-chain structures in highly excited states of $^{14}$C using a generalized molecular orbital model, by which we incorporate an asymmetric configuration of three $α$ clusters in the linear-chain states. By applying this model to the $^{14}$C system, we study the $^{10}$Be+$α$ correlation in the linear-chain state of $^{14}$C. To clarify the origin of the $^{10}$Be+$α$ correlation in the $^{14}$C linear-chain state, we analyze linear $3α$ and $3α+n$ systems in a similar way. We find that a linear 3$α$ system prefers the asymmetric 2$α+α$ configuration, whose origin is the many body correlation incorporated by the parity projection. This configuration causes an asymmetric mean field for two valence neutrons, which induces the concentration of valence neutron wave functions around the correlating 2$α$. A linear-chain structure of $^{16}$C is also discussed.

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arXiv2011

Two-neutron correlations in microscopic wave functions of He-6, He-8 and C-12

Two-neutron densities obtained from microscopic wave functions of $^6$He and $^8$He are investigated to reveal di-neutron correlations. In particular, the comparison of the two-neutron density with the product of one-neutron densities is useful for a quantitative discussion of di-neutron correlations. The calculations show that the S=0 spatial two-neutron correlation increases at the surface of $^6$He$(0^+_1)$ and $^8$He$(0^+_2)$. The enhancement is remarkable in the $^6$He$(0^+_1)$ ground state but not as prominent in the $^8$He$(0^+_1)$ ground state. Configuration mixing of many Slater determinants is essential to describe the di-neutron correlations. Two-neutron densities in $^{12}$C wave functions with $α$-cluster structures are also studied.

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arXiv2011

A new approach to investigate dineutron correlation and its application to $^{10}$Be

We propose a new framework by means of the dineutron condensate (DC) wave function to describe the dineutron correlation, which is characterized by the spatially strong correlation of a spin-zero neutron-neutron pair, in neutron-rich nuclei with an active deformed core surrounded by valence neutrons. Using the DC wave function for a 2$α$+2n system, which corresponds to a toy model for the $^{10}$Be system, we investigate the neutron-neutron correlation around the $2α$ core and discuss the mechanism of the dineutron formation at the surface of finite nuclei. To investigate dineutron correlations in realistic nuclear systems, we superpose the antisymmetrized molecular dynamics (AMD) wave functions and the DC wave functions. Applying the AMD+DC method to $^{10}$Be, we show effects of the DC wave functions in the ground and excited $0^+$ states of $^{10}$Be and discuss the dineutron correlation in them.

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arXiv2011

Alpha-cluster structure and density wave in oblate nuclei

Pentagon and triangle shapes in Si-28 and C-12 are discussed in relation with nuclear density wave. In the antisymmetrized molecular dynamics calculations, the $K^π=5^-$ band in Si-28 and the $K^π=3^-$ band in C-12 are described by the pentagon and triangle shapes, respectively. These negative-parity bands can be interpreted as the parity partners of the $K^π=0^+$ ground bands and they are constructed from the parity-asymmetric-intrinsic states. The pentagon and the triangle shapes originate in 7alpha and 3alpha cluster structures, respectively. In a mean-field picture, they are described also by the static one-dimensional density wave at the edge of the oblate states. In analysis with ideal alpha cluster models using Brink-Bloch cluster wave functions and that with a simplified model, we show that the static edge density wave for the pentagon and triangle shapes can be understood by spontaneous breaking of axial symmetry, i.e., the instability of the oblate states with respect to the edge density wave. The density wave is enhanced in the Z=N nuclei due to the proton-neutron coherent density waves, while it is suppressed in Z\ne N nuclei.

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arXiv2011

Proton dominance in the 2^+_2 -> 0^+_1 transition of N = Z\pm 2 nuclei around Si-28

E2 transitions in Si-30 are investigated in relation with intrinsic deformations based on a method of antisymmetrized molecular dynamics. By comparing E2 transition strengths in the mirror nuclei Si-30 and S-30, transition matrix amplitudes M_p and M_n for protons and neutrons are discussed in mirror analysis. Particular attention is paid to the M_n/M_p ratio in the transition from the 2^+_2 state to the 0^+_1 state. The M_n/M_p ratio in Mg-26 and Si-26 is also investigated. It is found that the proton dominance in the transition 2^+_2 -> 0^+_1 in Si-30 and Si-26 originates in the oblate trend of the Z=14 proton structure.

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arXiv2011

Cluster structures of excited states in $^{14}$C

Structures of excited states in $^{14}$C are investigated with a method of $β$-$γ$ constraint antisymmetrized molecular dynamics in combination with the generator coordinate method. Various excited states with the developed $3α$-cluster core structures are suggested in positive- and negative-parity states. In the positive-parity states, triaxial deformed and linear-chain structures are found to construct excited bands. Interestingly, $^{10}$Be+$α$ correlation is found in the cluster states above the $^{10}$Be+$α$ threshold energy.

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