arXiv subjects

Kazuyuki Ogata

Publications and source records attributed to Kazuyuki Ogata.

At least 55 records · Page 3Linked to original sources

arXiv2020

Transition properties of low-lying states in $^{28}$Si probed via inelastic proton and alpha scattering

$0^+$, $1^-$, $2^+$, and $3^-$ excitations of $^{28}\textrm{Si}$ are investigated via proton and $α$ inelastic scattering off $^{28}\textrm{Si}$. The structure calculation of $^{28}\textrm{Si}$ is performed with the energy variation after total angular momentum and parity projections in the framework of antisymmetrized molecular dynamics (AMD). As a result of the AMD calculation, the oblate ground and prolate bands, $0^+$ and $3^-$ excitations, and the $1^-$ and $3^-$ states of the $K^π=0^-$ band are obtained. Using the matter and transition densities of $^{28}\textrm{Si}$ obtained by AMD, microscopic coupled-channel calculations of proton and $α$ scattering off $^{28}\textrm{Si}$ are performed. The proton-$^{28}\textrm{Si}$ potentials in the reaction calculation are microscopically derived by folding the Melbourne $g$-matrix $NN$ interaction with the AMD densities of $^{28}\textrm{Si}$. The $α$-$^{28}\textrm{Si}$ potentials are obtained by folding the nucleon-$^{28}\textrm{Si}$ potentials with an $α$ density. The calculation reasonably reproduces the observed elastic and inelastic cross sections of proton and $α$ scattering. Transition properties are discussed by combining the reaction analysis of proton and $α$ scattering and structure features such as transition strengths and form factors. The isoscalar monopole and dipole transitions are focused.

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arXiv2019

Toward a reliable description of ${(p,pN)}$ reactions in the distorted-wave impulse approximation

Background: Proton-induced nucleon knockout $(p,pN)$ reactions have been successfully used to study the single-particle nature of stable nuclei in normal kinematics with the distorted-wave impulse approximation (DWIA) framework. Recently, these reactions have been applied to rare-isotope beams at intermediate energies in inverse kinematics to study the quenching of spectroscopic factors. Purpose: Our goal is to investigate the effects of various corrections and uncertainties within the standard DWIA formalism on the $(p,pN)$ cross sections. The consistency of the extracted reduction factors between DWIA and other methods is also evaluated. Method: We analyze the $(p,2p)$ and $(p,pn)$ reactions data measured at the R$^3$B/LAND setup at GSI for carbon, nitrogen, and oxygen isotopes in the incident energy range of 300--450 MeV/u. Cross sections and reduction factors are calculated by using the DWIA method. The transverse momentum distribution of the $^{12}$C($p$,$2p$)$^{11}$B reaction is also investigated. Results: We have found that including the nonlocality corrections and the Møller factor affects the cross sections considerably. The proton-neutron asymmetry dependence of reduction factors extracted by the DWIA calculation is very weak and consistent with those given by other reaction methods and \textit{ab initio} structure calculations. Conclusions: The results found in this work provide a detailed investigation of the DWIA method for $(p,pN)$ reactions at intermediate energies. They also suggest that some higher-order effects, which is essential for an accurate cross-section description at large recoil momentum, is missing in the current DWIA and other reaction models.

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arXiv2019

Quantitative description of the $^{20}$Ne($p$,$pα$)$^{16}$O cross section as a means of probing the surface $α$ amplitude

The proton-induced $α$ knockout reaction has been utilized for decades to investigate the $α$ cluster states of nuclei, of the ground state in particular. However, even in recent years, it is reported that the deduced $α$ spectroscopic factors from $α$ knockout experiments and reaction analyses with a phenomenological $α$ cluster wave function diverge depending on the kinematical condition of the reaction. In the present study we examine the theoretical description of the $^{20}$Ne($p$,$pα$)$^{16}$O cross section based on the antisymmetrized molecular dynamics and the distorted wave impulse approximation by comparing with existing experimental data. We also investigate the correspondence between the $α$ cluster wave function and the $α$ knockout cross section. The existing $^{20}$Ne($p$,$pα$)$^{16}$O data at 101.5 MeV is well reproduced by the present framework. Due to the peripherality of the reaction, the surface region of the cluster wave function is selectively reflected to the knockout cross section. A quantitatively reliable $α$ cluster wave function, $p$-$α$ cross section, and distorting potentials between scattering particles, $α$-$^{16}$O in particular, are crucial for the quantitative description of the ($p$,$pα$) cross section. Due to the peripherality of the reaction, the ($p$,$pα$) cross section is a good probe for the surface $α$ amplitude.

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arXiv2019

Cluster structures and monopole transitions of $^{14}$C

Cluster structures of $^{14}$C were investigated with a method of antisymmetrized molecular dynamics (AMD) combined with a $3α+nn$ cluster model while focusing on the monopole excitations and linear-chain $3α$ band. Variation after parity and angular momentum projections was performed in the AMD framework, and the generator coordinate method was applied to take into account various $3α+nn$ cluster configurations. Energy spectra and monopole and $E2$ transition strengths of $0^+$, $2^+$, and $4^+$ states were calculated to assign band structures. The $0^+_3$ state with remarkable monopole transition was obtained as a vibrational mode of the triangle $3α$ configuration. In addition, the linear-chain $3α$ band from the band-head $0^+_4$ state was obtained. $^{10}$Be$+α$ decay widths of $0^+$, $2^+$, and $4^+$ states were evaluated. $α$ inelastic scattering off $^{14}$C was also investigated by the microscopic coupled-channel calculation with the $g$-matrix folding model to propose possible observation of the $0^+_3$ state via $α$ scattering experiments.

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arXiv2019

Effect of the repulsive core in the proton-neutron potential on deuteron elastic breakup cross sections

The role of the short-range part (repulsive core) of the proton-neutron ($pn$) potential in deuteron elastic breakup processes is investigated. A simplified one-range Gaussian potential and the Argonne V4' (AV4') central potential are adopted in the continuum-discretized coupled-channels (CDCC) method. The deuteron breakup cross sections calculated with these two potentials are compared. The repulsive core is found not to affect the deuteron breakup cross sections at energies from 40 MeV to 1 GeV. To understand this result, an analysis of the peripherality of the elastic breakup processes concerning the $p$-$n$ relative coordinate is performed. It is found that for the breakup processes populating the $pn$ continua with orbital angular momentum $\ell$ different from 0, the reaction process is peripheral, whereas it is not for the breakup to the $\ell=0$ continua (the s-wave breakup). The result of the peripherality analysis indicates that the whole spatial region of deuteron contributes to the s-wave breakup.

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arXiv2019

Microscopic calculation of inelastic proton scattering off $^{18}$O, $^{10}$Be, $^{12}$Be, and $^{16}$C for study of neutron excitation in neutron-rich nuclei

The microscopic coupled-channel calculation of inelastic proton scattering is performed for the study of neutron excitations in $2^+_1$ states of $^{18}$O, $^{10}$Be, $^{12}$Be, and $^{16}$C. Proton-nucleus potentials in the coupled-channel calculation are microscopically derived by folding the Melbourne $g$-matrix $NN$ interaction with matter and transition densities of target nuclei obtained by the structure model calculation of antisymmetrized molecular dynamics. The calculated result reasonably reproduces the elastic and inelastic proton scattering cross sections, and supports the dominant contribution of neutron in the $2^+_1$ excitation of $^{12}$Be and $^{16}$C as well as $^{18}$O. Sensitivity of the inelastic scattering cross sections to the neutron transition density is discussed. The exotic feature of the neutron transition density with the amplitude in the outer region in $^{12}$Be and $^{16}$C is focused.

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arXiv2019

Borromean Feshbach resonance in 11Li studied via 11Li(p,p')

A dipole resonance of 11Li is newly found by a 9Li + n + n three-body model analysis with the complex-scaling method. The resonance can be interpreted as a bound state in the 10Li + n system, that is, a Feshbach resonance in the 9Li + n + n system. As a characteristic feature of the Feshbach resonance of 11Li, the 10Li + n threshold is open above the 9Li + n + n one, which reflects a distinctive property of the Borromean system. A microscopic four-body reaction calculation for the 11Li(p,p') reaction at 6 MeV/nucleon is performed by taking into account the resonance and nonresonant continuum states of the three-body system. The angular distribution of the elastic and inelastic scattering as well as the breakup energy spectrum recently observed are reproduced well.

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arXiv2019

Direct probing of the cluster structure in ${}^{12}$Be via $α$-knockout reaction

Background: Recent theoretical and experimental researches using proton-induced $α$-knockout reactions provide direct manifestation of $α$-cluster formation in nuclei. In recent and future experiments, $α$-knockout data are available for neutron-rich beryllium isotopes. In $^{12}$Be , rich phenomena are induced by the formation of $α$-clusters surrounded by neutrons, for instance, breaking of the neutron magic number $N=8$. Purpose: Our objective is to provide direct probing of the $α$-cluster formation in the $^{12}$Be target through associating the structure information obtained by a microscopic theory with the experimental observables of $α$-knockout reactions. Method: We formulate a new wave function of the Tohsaki-Horiuchi-Schuck-R{ö}pke (THSR) type for the structure calculation of ${}^{12}$Be nucleus and integrate it with the distorted wave impulse approximation framework for the $α$-knockout reaction calculation of $^{12}$Be$(p,pα)^{8}$He. Results: We reproduce the low-lying spectrum of the $^{12}$Be nucleus using the THSR wave function and discuss the cluster structure of the ground state. Based on the microscopic wave function, the optical potentials and $α$-cluster wave function are determined and utilized in the calculation of ${}^{12}$Be($p,pα$)${}^{8}$He reaction at 250 MeV. The possibility of probing the clustering state of $^{12}$Be through this reaction is demonstrated by analysis of the triple differential cross sections that are sensitively dependent on the $α$-cluster amplitude at the nuclear surface. Conclusions: This study provides a feasible approach to validate directly the theoretical predictions of clustering features in the $^{12}$Be nucleus through the $α$-knockout reaction.

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arXiv2019

Large-amplitude quadrupole shape mixing probed by the $(p,p^\prime)$ reaction : a model analysis

To discuss a possible observation of large-amplitude nuclear shape mixing by nuclear reaction, we employ a simple collective model and evaluate transition densities, with which the differential cross sections are obtained through the microscopic coupled-channel calculation. Assuming the spherical-to-prolate shape transition, we focus on large-amplitude shape mixing associated with the softness of the collective potential in the $β$ direction. We introduce a simple model based on the five-dimensional quadrupole collective Hamiltonian, which simulates a chain of isotopes that exhibit spherical-to-prolate shape phase transition. Taking $^{154}$Sm as an example and controlling the model parameters, we study how the large-amplitude shape mixing affects the elastic and inelastic proton scatterings. The calculated results suggest that the inelastic cross section of the $2_2^+$ state tells us an important role of the quadrupole shape mixing.

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arXiv2019

Investigation of spatial manifestation of $α$ clusters in $^{16}$O via $α$-transfer reactions

Recently, we have determined surface distributions of $α$ clusters in the ground state of $^{20}\mathrm{Ne}$ from $α$-transfer cross sections, without investigating the properties of its excited states. In this paper we extend our comprehension of $α$-cluster structures in excited states of nuclei through reaction studies. In particular we focus on $^{16}\mathrm{O}$, for which attention has been paid to advances of structure theory and assignment regarding $4^+$-resonance states. We study the surface manifestation of the $α$-cluster states in both the ground and excited states of $^{16}\mathrm{O}$ from the analysis of the $α$-transfer reaction $^{12}\mathrm{C}(^6\mathrm{Li},d)^{16}\mathrm{O}$. The $α$-transfer reaction is described by the distorted-wave Born approximation. We test two microscopic wave functions as an input of reaction calculations. Then a phenomenological potential model is introduced to clarify the correspondence between cluster-wave functions and transfer-cross sections. Surface peaks of the $α$-wave function of $^{16}\mathrm{O}(0^+)$ are sensitively probed by transfer-cross sections at forward angles, while it remains unclear how we trace the surface behavior of $^{16}\mathrm{O}(4^+)$ from the cross sections. We are able to specify that the $α$-cluster structure in the $0_1^+$ and $0_2^+$ states prominently manifests itself at the radii $\sim 4$ and $\sim 4.5$~fm, respectively. It is remarkable that the $4_1^+$ state has the $^{12}\mathrm{C}+α$-cluster component with the surface peak at the radius $\sim 4$ or outer, whereas the $^{12}\mathrm{C}+α$-cluster component in the $4_2^+$ state is found not to be dominant. The $4_2^+$ state is difficult to be interpreted by a simple potential model assuming the $^{12}\mathrm{C}+α$ configuration only.

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arXiv2019

First microscopic coupled-channel calculation of $α$ inelastic cross sections on $^{16}$O

The $α$ inelastic scattering on $^{16}$O is investigated with the coupled-channel calculation using the $α$-nucleus coupled-channel potentials, which are microscopically derived by folding the the Melbourne $g$-matrix $NN$ interaction with the $^{16}$O and $α$ densities. The matter and transition densities of $^{16}$O are calculated by a microscopic structure model of the variation after the spin-parity projections combined with the generator coordinate method of $^{12}$C+$α$ in the framework of the antisymmetrized molecular dynamics. The calculation reproduces the observed elastic and inelastic cross sections at incident energies of $E_α$=104 MeV, 130 MeV, 146 MeV, and 386 MeV. The coupled-channel effect on the cross sections is also discussed.

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arXiv2019

$α$ scattering cross sections on $^{12}$C with microscopic coupled-channel calculation

$α$ elastic and inelastic scattering on $^{12}$C is investigated with the coupled-channel calculation using microscopic $α$-$^{12}$C potentials, which are derived by folding the Melbourne $g$-matrix $NN$ interaction with the matter and transition densities of $^{12}$C. These densities are obtained by a microscopic structure model of the antisymmetrized molecular dynamics combined with and without the $3α$ generator coordinate method. The calculation reproduces satisfactorily well the observed elastic and inelastic cross sections at incident energies of $E_α=130$~MeV, 172.5~MeV, 240~MeV, and 386~MeV with no adjustable parameter. Isoscalar monopole and dipole excitations to the $0^+_2$, $0^+_3$, and $1^-_1$ states in the $α$ scattering are discussed.

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arXiv2018

Investigation of $α$ clustering with knockout reactions

Our goal is to reveal how the $α$ cluster amplitude is probed through $α$ knockout reactions depending on reaction conditions, e.g., the incident energy. We consider $^{20}$Ne($p$,$pα$)$^{16}$O and $^{120}$Sn($p$,$pα$)$^{116}$Cd at 100-400 MeV within the distorted wave impulse approximation (DWIA) framework. We introduce a masking function which shows how the reaction amplitude in the nuclear interior is suppressed and defines the probed region of the $α$ cluster wave function. It is clearly shown by means of the masking function that the $α$ knockout reaction probes the $α$ cluster amplitude in the nuclear surface region, which is the direct measure of well-developed $α$ cluster states. A simplified form of the masking function is introduced and the incident energy dependence of the masking effect is investigated. $α$ knockout reaction can probe the $α$ cluster amplitude in the nuclear surface region by choosing proper kinematics owing to the masking effect originated from absorptions of distorting potentials, and is a suitable method to investigate how $α$ cluster states are spatially developed.

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arXiv2018

Manifestation of α-clustering in $^{10}$Be via α-knockout reaction

Background: Proton-induced α-knockout reactions empower direct experimental manifestations of α-clustering in nuclei. This is obtained by relating the theoretical descriptions of clustering states with experimental reaction observables. It is desired to introduce microscopic structure models into the theoretical frameworks for α-knockout reactions. Purpose: Our goal is to probe the α-clustering in $^{10}$Be nucleus by proton-induced α-knockout reaction observables. Method: We adopt an extended version of the Tohsaki-Horiuchi-Schuck-Röpke (THSR) wave function of $^{10}$Be and integrate it with the distorted wave impulse approximation (DWIA) framework for the calculation of (p,pα) knockout reactions. Results: We make the first calculation for the $^{10}$Be(p,pα)$^{6}$He reaction at 250 MeV implementing a microscopic α-cluster wave function and predict the triple differential cross sections (TDX). Furthermore, by constructing artificial states of the target nucleus $^{10}$Be with compact or dilute spatial distributions, the TDX is found to be highly sensitive to the extent of clustering in the target nuclei. Conclusions: These results provide reliable manifestation of the α-clustering in $^{10}$Be.

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arXiv2018

Azimuthal angle distributions of neutrons emitted from the $^9$Be($γ$,$n$) reaction with linearly polarized $γ$-rays

The electromagnetic transitions of $^9$Be with linearly polarized $γ$-rays are calculated by using the $α$~+~$α$~+~$n$ three-body model and the complex-scaled solutions of the Lippmann-Schwinger equation; the azimuthal angle distributions of the emitted neutrons are investigated. We calculate the anisotropy parameter as a function of the photon incident energy $E_γ$, and discuss how sensitive the anisotropy parameter is to nuclear structure and transition modes. The result suggests that the azimuthal angle distribution of neutrons emitted from the $^9$Be($γ$,$n$) reaction with the linearly polarized $γ$-rays is useful to identify the resonances in the final states even if it is not clearly observed in the cross section.

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arXiv2018

Quantum mechanical description of excitation energy distribution of the reaction residue in nucleon-induced inclusive one-nucleon knockout reactions

Understanding of inclusive one-nucleon knockout reactions for long-lived fission fragments (LLFPs) is crucial for nuclear transmutation studies. However, the particle and heavy ion transport code system (PHITS) severely overshoots the inclusive one-nucleon knockout cross sections sigma_-1N. Therefore development of a reaction model for describing the inclusive one-nucleon knockout processes is necessary. A key is specification of the position and the momentum of a nucleon inside a nucleus to be struck by the incident nucleon. In this paper the semiclassical distorted wave model incorporating the Wigner transform of the one-body nuclear density matrix is applied to the calculation of excitation energy distributions of reaction residues. Decay of a residue is described by introducing a threshold parameter for the minimum excitation energy of it. With reasonable values of the parameter, the measured sigma_-1N for several LLFPs are reproduced by the proposed reaction model. The incident energy dependence of sigma_-1N is found to be governed by that of the nucleon-nucleon cross sections at energies higher than about 75 MeV. At low energies, the nuclear absorption and the Coulomb penetrability also become important. The energy dependence of neutron-induced sigma_-1N is predicted and found to be quite different from that of proton induced one. The proposed reaction model is shown to be promising in discussing the energy dependence of nucleon-induced inclusive one-nucleon knockout processes. The energy dependence of the measured sigma_-1p for 107Pd above 100 MeV is, however, not explained by the present calculation.

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arXiv2017

Reexamination of microscopic optical potentials based on multiple scattering theory

Microscopic optical potentials have been successful in describing nucleon-nucleus and nucleus-nucleus scattering. Some essential ingredients of the framework, however, have not been examined in detail. Applicability of the microscopic folding model is systematically investigated. Effect of an antisymmetrization factor (ASF) appearing in multiple scattering theory, theoretical uncertainty regarding the local density approximation (LDA), and the validity of a prescription for nonlocality, the Brieva-Rook (BR) localization, of the microscopic potential, are quantitatively estimated for nucleon-nucleus scattering; investigation on the ASF is carried out for also deuteron-nucleus scattering. A single folding model with the Melbourne g-matrix interaction and the SLy4 Skyrme-type Hartree-Fock-Bogoliubiv (SLy4-HFB) density is employed for evaluating a nucleon-nucleus microscopic optical potential. Deuteron-nucleus scattering is described by the continuum-discretized coupled-channels method incorporating the microscopic proton-nucleus and neutron-nucleus potentials. The ASF is found to affect proton total reaction cross sections for a 12C target below 200 MeV by about 10%. Effect of the ASF on total reaction cross sections is negligibly small if a target nucleus is heavy or scattering energy is above 200 MeV; elastic cross sections are hardly affected by the ASF for all the reaction systems considered. Below 65 MeV, still the BR localization works quite well. However, at energies below about 50 MeV, the LDA becomes less accurate for evaluating elastic cross sections at backward angles. This is the case also for the total reaction cross sections of p-12C below about 200 MeV. The microscopic model is applicable to nucleon-nucleus scattering above 25 MeV for target nuclei in a wide range of mass numbers. Deviation of calculated results from experimental data is less than about 10%.

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arXiv2017

Probing three-nucleon-force effects via (p,2p) reactions

We propose to use proton knockout reactions (p,2p) from a deeply bound orbit as a new probe into three-nucleon-force (3NF) effects. The remarkable advantage of using (p,2p) reaction is that we can choose an appropriate kinematical condition to probe the 3NF effects. We analyze (p,2p) reactions on a 40Ca target within the framework of distorted-wave impulse approximation with a g-matrix interaction based on chiral two- and three-nucleon forces. The chiral 3NF effects significantly change the peak height of the triple differential cross section of (p,2p) reaction. We also clarify the correspondence between the (p,2p) cross sections and the in- medium pp cross sections.

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