arXiv subjects

Yoshiko Kanada-En'yo

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

At least 73 records · Page 4Linked to original sources

arXiv2016

$α$-cluster excited states in $^{32}$S

$α$-cluster excited states in $^{32}$S are investigated with an extended $^{28}$Si+$α$ cluster model, in which the $^{28}$Si core deformation and rotation, and the $α$-cluster breaking are incorporated. In the GCM calculation with the extended $^{28}$Si+$α$ cluster model, the $α$-cluster excited states are obtained near the $^{28}$Si+$α$ threshold energy. The $^{28}$Si core deformation and rotation effects, and also the $α$-clusters breaking in the $^{28}$Si+$α$ system are discussed. It is found that the rotation of the oblately deformed $^{28}$Si core gives a significant effect to the $α$-cluster excited states whereas the $α$-cluster breaking gives only a minor effect.

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arXiv2015

Isovector and isoscalar dipole excitations in $^{9}$Be and $^{10}$Be studied with antisymmetrized molecular dynamics

Isovector and isoscalar dipole excitations in $^9$Be and $^{10}$Be are investigated in the framework of antisymmetrized molecular dynamics, in which angular-momentum and parity projections are performed. In the present method, 1p-1h excitations on the ground state and large amplitude $α$-cluster mode are incorporated. The isovector giant dipole resonance (GDR) in $E>20$ MeV shows the two peak structure which is understood by the dipole excitation in the 2$α$ core part with the prolate deformation. Because of valence neutron modes against the $2α$ core, low-energy E1 resonances appear in $E<20$ MeV exhausting about $20\%$ of the Thomas-Reiche-Kuhn sum rule and $10\%$ of the calculated energy-weighted sum. The dipole resonance at $E\sim 15$ MeV in $^{10}$Be can be interpreted as the parity partner of the ground state having a $^6$He+$α$ structure and has the remarkable E1 strength because of coherent contribution of two valence neutrons. The ISD strength for some low-energy resonances are significantly enhanced by the coupling with the $α$-cluster mode. The calculated E1 strength of $^9$Be reasonably describes the global feature of experimental photonuclear cross sections consisting of the low-energy strength in $E<20$ MeV and the GDR in $E>20$ MeV.

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arXiv2015

Isoscalar monopole and dipole excitations of cluster states and giant resonances in $^{12}$C

The isoscalar monopole(ISM) and dipole(ISD) excitations in $^{12}$C are theoretically investigated with the shifted antisymmetrized molecular dynamics(AMD) plus $3α$-cluster generator coordinate method(GCM). The small amplitude vibration modes are described by coherent one-particle one-hole excitations expressed by small shift of single-nucleon Gaussian wave functions within the AMD framework, whereas the large amplitude cluster modes are incorporated by superposing $3α$-cluster wave functions in the GCM. The coupling of the excitations in the intrinsic frame with the rotation and parity transformation is taken into account microscopically by the angular-momentum and parity projections. The present calculation describes the ISM and ISD excitations in a wide energy region covering cluster modes in the low-energy region and the giant resonances in the high-energy region, though the quantitative description of the high-energy part is not satisfactory. The low-energy ISM and ISD strengths of the cluster modes are enhanced by the radial motion of $α$ clusters, and they split into a couple of states because of the angular motion of $α$ clusters. The low-energy ISM strengths exhaust 26% of the EWSR, which is consistent with the experimental data for the $^{12}$C($0^+_2$;7.65 MeV) and $^{12}$C($0^+_3$;10.3 MeV) measured by $(e,e')$, $(α,α')$, and ($^6$Li,$^6$Li$'$) scatterings. In the calculated low-energy ISD strengths, two $1^-$ states (the $1^-_1$ and $1^-_2$) with the significant strengths are obtained in $E=10-15$ MeV. It is indicated that the ISD excitations can be a good probe to experimentally search for new cluster states such as the $^{12}$C($1^-_2$) obtained in the present calculation.

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arXiv2015

Analysis of the effect of core structure upon dineutron correlation using antisymmetrized molecular dynamics

We extend the method of antisymmetrized molecular dynamics to investigate dineutron correlation. We apply this method to $^{10}$Be as an example and investigate the motion of two neutrons around a largely deformed $^8$Be core by analyzing the two-neutron overlap function around the core. We show that the core structure plays an important role in dineutron formation and expansion from the core and that the present framework is effective for the studies of dineutron correlation.

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arXiv2015

$^{10}$B+$α$ states with chain-like structures in $^{14}$N

I investigate $^{10}$B+$α$ cluster states of $^{14}$N with a $^{10}$B+$α$ cluster model. Near the $α$-decay threshold energy, I obtain $K^π=3^+$ and $K^π=1^+$ rotational bands having $^{10}$B($3^+$)+$α$ and $^{10}$B($1^+$)+$α$ components, respectively. I assign the band-head state of the $K^π=3^+$ band to the experimental $3^+$ at $E_x$=13.19 MeV of $^{14}$N observed in $α$ scattering reactions by $^{10}$B and show that the calculated $α$-decay width is consistent with the experimental data. I discuss an $α$-cluster motion around the $^{10}$B cluster and show that $^{10}$B+$α$ cluster states contain significant components of a linear-chain 3$α$ configuration, in which an $α$ cluster is localized in the longitudinal direction around the deformed $^{10}$B cluster.

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arXiv2015

Proton and neutron correlations in $^{10}$B

We investigate positive-parity states of $^{10}$B with the calculation of antisymmetrized molecular dynamics focusing on $pn$ pair correlations. We discuss effects of the spin-orbit interaction on energy spectra and $pn$ correlations of the $J^πT=1^+_10$, $=3^+_10$, and $0^+_11$ states. The $1^+_10$ state has almost no energy gain of the spin-orbit interaction, whereas the $3^+_10$ state gains the spin-orbit interaction energy largely to come down to the ground state. We interpret a part of the two-body spin-orbit interaction in the adopted effective interactions as a contribution of the genuine $NNN$ force, and find it to be essential for the level ordering of the $3^+_10$ and $1^+_10$ states in $^{10}$B. We also apply a $2α+pn$ model to discuss effects of the spin-orbit interaction on $T=0$ and $T=1$ $pn$ pairs around the 2$α$ core. In the spin-aligned $J^πT=3^+0$ state, the spin-orbit interaction affects the $(ST)=(10)$ pair attractively and keeps the pair close to the core, whereas, in the $1^+0$ state, it gives a minor effect to the $(ST)=(10)$ pair. In the $0^+1$ state, the $(ST)=(01)$ pair is somewhat dissociated by the spin-orbit interaction.

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arXiv2015

Effects of $α$-cluster breaking on 3$α$ cluster structures in $^{12}$C

To clarify the effects of $α$-cluster breaking on 3$α$ cluster structures in $^{12}$C, we investigate $^{12}$C using a hybrid model that combines the Brink-Bloch cluster model with the $p_{3/2}$ subshell closure wave function. We have found that $α$-cluster breaking caused by spin-orbit force significantly changes cluster structures of excited $0^{+}$ states through orthogonality to lower states. Spatially developed cluster components of the $0^{+}_{2}$ state are reduced. The $0^{+}_{3}$ state changes from a vibration mode in the bending motion of three $α$ clusters to a chain-like 3$α$ structure having an open triangle configuration. As a result of these structure changes of $0^{+}$ states, the band assignment for the $2^{+}_{2}$ state is changed by the $α$-cluster breaking effect. Namely, in model calculations without the $α$-cluster breaking effect, the $0^{+}_{2}$ state is assigned to be the band-head of the $2^{+}_{2}$ state. However, when we incorporate $α$-cluster breaking caused by the spin-orbit force, the $0^{+}_{3}$ state is regarded as the band-head of the $2^{+}_{2}$ state.

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arXiv2015

Quantum decoherence in the entanglement entropy of a composite particle and its relationship to coarse graining in the Husimi function

I investigate quantum decoherence in a one-body density matrix of a composite particle consisting of two correlated particles. Because of a two-body correlation in the composite particle, quantum decoherence occurs in the one-body density matrix that has been reduced from the two-body density matrix. As the delocalization of the distribution of the composite particle grows, the entanglement entropy increases, and the system can be well-described by a semi-classical approximation, wherein the center position of the composite particle can be regarded as a classical coordinate. I connect the quantum decoherence in the one-body density matrix of a composite particle to the coarse graining in a phase space distribution function of a single particle and associate it with the Husimi function.

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arXiv2015

Entanglement entropy and Schmidt number as measures of delocalization of $α$ clusters in one-dimensional nuclear systems

We calculated the von Neumann entanglement entropy and the Schmidt number of one dimentional (1D) cluster states and showed that these are useful measures to estimate entanglement caused by delocalization of clusters. We analyze system size dependence of these entanglement measures in the linear-chain $nα$ states given by Tohsaki-Horiuchi-Schuck-Röpke wave functions for 1D cluster gas states. We show that the Schmidt number is an almost equivalent measures to the von Neumann entanglement entropy when the delocalization of clusters occurs in the entire system but it shows different behaviors in a partially delocalized state containing localized clusters and delocalized ones. It means that the Rényi-2 entanglement entropy, which relates to the Schmidt number, is found to be almost equivalent to the von Neumann entanglement entropy for the full delocalized cluster system but it is less sensitive to the partially delocalized cluster system than the von Neumann entanglement entropy. We also propose a new entanglement measure which has a generalized form of the Schmidt number. Sensitivity of these measures of entanglement to the delocalization of clusters in low-density regions was discussed.

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arXiv2015

Analysis of delocalization of clusters in linear-chain $α$-cluster states with entanglement entropy

I investigate entanglement entropy of one dimension (1D) cluster states to discuss the delocalization of clusters in linear-chain $3α$- and $4α$-cluster states. In analysis of entanglement entropy of 1D Tohsaki-Horiuchi-Schuck-Röpke (THSR) and Brink-Bloch cluster wave functions, I show clear differences in the entanglement entropy between localized cluster wave functions and delocalized cluster wave functions. In order to clarify spatial regions where the entanglement entropy is generated by the delocalization of clusters, I analyze the spatial distribution of entanglement entropy. In the linear-chain $3α$ cluster state, the delocalization occurs dominantly in a low-density tail region while it is relatively suppressed in an inner region because of Pauli blocking effect between clusters. In the linear-chain 4$α$ state having a larger system size than the linear-chain $3α$ state, the delocalization occurs in the whole system. The entanglement entropy is found to be a measure of the delocalization of clusters in the 1D cluster systems.

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arXiv2014

Proton radii of Be, B, and C isotopes

We investigate the neutron number $(N)$ dependence of root mean square radii of point proton distribution (proton radii) of Be, B, and C isotopes with the theoretical method of variation after spin-parity projection in the framework of antisymmetrized molecular dynamics (AMD). The proton radii in Be and B isotopes changes rapidly as $N$ increases, reflecting the cluster structure change along the isotope chains, whereas, those in C isotopes show a weak $N$ dependence because of the stable proton structure in nuclei with $Z=6$. In neutron-rich Be and B isotopes, the proton radii are remarkably increased by the enhancement of the two-center cluster structure in the prolately deformed neutron structure. We compare the $N$ dependence of the calculated proton radii with the experimental ones reduced from the charge radii determined by isotope shift and those deduced from the charge changing interaction cross section. It is found that the $N$ dependence of proton radii can be a probe to clarify enhancement and weakening of cluster structures.

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arXiv2014

2alpha+t cluster feature of $3/2^-_3$ state in $^{11}$B

We reanalyze $2α+t$ cluster features of $3/2^-$ states in $^{11}$B by investigating the $t$ cluster distribution around a $2α$ core in $^{11}$B, calculated with the method of antisymmetrized molecular dynamics (AMD). In the $3/2^-_3$ state, a $t$ cluster is distributed in a wide region around $2α$, indicating that the $t$ cluster moves rather freely in angular as well as radial motion. From the weak angular correlation and radial extent of the $t$ cluster distribution, we propose an interpretation of a $2α+t$ cluster gas for the $3/2^-_3$ state. In this study, we compare the $2α+t$ cluster feature in $^{11}$B($3/2^-_3$) with the $3α$ cluster feature in $^{12}$C($0^+_2$), and discuss their similarities and differences.

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arXiv2014

Description of $α$-cluster tail in $^{8}$Be and $^{20}$Ne: Delocalization of $α$ cluster because of quantum penetration

We analyze the $α$-cluster wave functions in cluster states of $^8$Be and $^{20}$Ne by comparing the exact relative wave function obtained by the generator coordinate method (GCM) with various types of trial functions. For the trial functions, we adopt the fixed range shifted Gaussian of the Brink-Bloch (BB) wave function, the spherical Gaussian with the adjustable range parameter of the spherical Thosaki-Horiuchi-Schuck-Röpke (sTHSR), the deformed Gaussian of the deformed THSR (dTHSR), and a function with the Yukawa tail (YT). The quality of the description of the exact wave function with a trial function is judged by the squared overlap between the trial function and the GCM wave function. The better result is obtained with the sTHSR wave function than the BB wave function, and further improvement can be done with the dTHSR wave function because these wave functions can describe the outer tail better. The YT wave function gives almost the equal quality to or even better quality than the dTHSR wave function indicating that the outer tail of $α$ cluster states is characterized by the Yukawa-like tail rather than the Gaussian tail. In the weakly bound $α$ cluster states with the small $α$ separation energy and the low centrifugal and Coulomb barriers, the outer tail part is the slowly damping function described well by the quantum penetration through the effective barrier. This outer tail characterizes the almost zero-energy free $α$ gas behavior, i.e., the delocalization of cluster.

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arXiv2014

Parity mixing of pair at nuclear surface due to spin-orbit potential in $^{18}$F

We investigate the structure of $^{18}$F with the microscopic wave function based on the three-body $^{16}$O+$p$+$n$ model. In the calculation of the generator coordinate method (GCM) of the three-body model, $T=0$ energy spectra of $J^π=1^+$, $3^+$, and $5^+$ states and $T=1$ spectra of $J^π=0^+$, $2^+$ states in $^{18}$F are described reasonably. Based on the dinucleon picture, the effect of the spin-orbit force on the $T=0$ and $T=1$ $pn$ pairs around the $^{16}$O core is discussed. The $T=1$ pair in the $J^π=0^+$ state gains the spin-orbit potential energy involving the odd-parity mixing in the pair. The spin-orbit potential energy gain with the parity mixing is not so efficient for the $T=0$ pair in the $J^π=1^+$ state. The parity mixing in the pair is regarded as the internal symmetry breaking of the pair in the spin-orbit potential at the nuclear surface.

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arXiv2014

Approximation of reduced width amplitude and application to cluster decay width

We propose a simple method to approximately evaluate reduced width amplitude (RWA) of a two-body spinless cluster channel using the norm overlap with the Brink-Bloch cluster wave function at the channel radius. The applicability of the present approximation is tested for the $^{16}$O+$α$ channel in $^{20}$Ne as well as the $α$+$α$ channel in $^8$Be. The approximation is found to be reasonable to evaluate the RWA for states near the threshold energy and it is useful to estimate the $α$-decay width of resonance states. The approximation is also applied to $^9$Li, and the partial decay width of the $^6$He($0^+_1$)+$t$ channel is discussed.

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arXiv2014

Gamov-Teller transitions from 14N ground to 14C ground and excited states

Gamov-Teller transitions from the $^{14}$N ground state to the $^{14}$C ground and excited states were investigated, based on the model of antisymmetrized molecular dynamics. The calculated strengths for the allowed transitions to the $0^+$, $1^+$, and $2^+$ states of $^{14}$C were compared with the experimental data measured by high-resolution charge-exchange reactions. The calculated GT transition to the $2^+_1$ state is strong while those to the $0^+_{2,3}$ and $2^+_{2,3}$ states having dominant $2\hbarω$ excited configurations are relatively weak. The present calculation can not describe the anonymously long life time of $^{14}$C, though the strength of the $^{14}$C ground state is somewhat suppressed because of the cluster (many-body) correlation in the ground states of $^{14}$C and $^{14}$N.

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arXiv2013

Folding model analysis of the inelastic $α+^{12}$C scattering at medium energies, and the isoscalar transition strengths of the cluster states of $^{12}$C

The complex optical potential and inelastic form factor given by the folding model for the $α+^{12}$C scattering are used to calculate the ($α,α'$) cross sections for the known isoscalar states of $^{12}$C in an elaborate coupled channel approach. The strengths of the form factors for these states are then fine tuned against the ($α,α'$) data to deduce the corresponding $Eλ$ transition strengths. A significant $E2$ transition strength has been obtained for the $2^+_2$ state from the present analysis of the ($α,α'$) data measured at $E_α=240$ and 386 MeV. The $Eλ$ transition strengths of the $0^+_2,\ 3^-_1,\ 0^+_3,$ and $1^-_1$ states were also carefully deduced, and some difference from the results of earlier analyses has been found and qualitatively understood.

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arXiv2013

Dinucleon correlation of $^9$Li, $^{10}$Be, and $^{9,10}$C

We study the dinucleon (dineutron and diproton) correlation of the ground states of $^9$Li, $^{10}$Be, and $^{9,10}$C. We assume an $α+t$ core for $^9$Li, an $α+α$ core for $^{10}$Be and $^{10}$C, and an $α+^3$He core for $^9$C, and investigate the effect of core structure changes on the degree of dineutron formation and spatial expansion from the core. For $^9$Li, $t$ cluster breaking in the core significantly enhances the dineutron component inside the nuclei. Moreover, its component markedly depends on the strength of the spin-orbit interaction since a dineutron is fragile and dissociates readily due to the spin-orbit interaction. Compared with $^9$Li, the dineutron of $^{10}$Be dissociates largely due to the stronger spin-orbit attraction from the $α+α$ core than the $α+t$ core. We also investigate diproton features in $^{9,10}$C, the mirror nuclei of $^9$Li and $^{10}$Be, respectively, and compare them with the dineutron features of $^9$Li and $^{10}$Be. No qualitative difference is observed between diprotons and dineutrons in the degree of formation at the surface, but a quantitative difference may exist in the degree of dinucleon-size change far from the core.

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