arXiv subjects

Kosho Minomo

Publications and source records attributed to Kosho Minomo.

At least 19 recordsLinked to original sources

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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arXiv2016

Microscopic effective reaction theory for deuteron-induced reactions

The microscopic effective reaction theory is applied to deuteron-induced reactions. A reaction model-space characterized by a $p+n+{\rm A}$ three-body model is adopted, where A is the target nucleus, and the nucleon-target potential is described by a microscopic folding model based on an effective nucleon-nucleon interaction in nuclear medium and a one-body nuclear density of A. The three-body scattering wave function in the model space is obtained with the continuum-discretized coupled-channels method (CDCC), and the eikonal reaction theory (ERT), an extension of CDCC, is applied to the calculation of neutron removal cross sections. Elastic scattering cross sections of deuteron on $^{58}$Ni and $^{208}$Pb target nuclei at several energies are compared with experimental data. The total reaction cross sections and the neutron removal cross sections at 56 MeV on 14 target nuclei are calculated and compared with experimental values.

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arXiv2016

Investigating the alpha-clustering on the surface of $^{120}$Sn via ($p$,$pα$) reaction and the validity of the factorization approximation

The $^{120}$Sn($p$,$pα$)$^{116}$Cd reaction at 392 MeV is investigated with the distorted wave impulse approximation (DWIA) framework. We show that this reaction is very peripheral mainly because of the strong absorption of $α$ by the reaction residue $^{116}$Cd, and the $α$-clustering on the nuclear surface can be probed clearly. We investigate also the validity of the so-called factorization approximation that has frequently been used so far. It is shown that the kinematics of $α$ in the nuclear interior region is significantly affected by the distortion of $^{116}$Cd, but it has no effect on the reaction observables because of the strong absorption in that region.

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arXiv2016

Deuteron-nucleus total reaction cross sections up to 1 GeV

Total reaction cross sections of deuteron, $σ_d^{\rm R}$, are calculated by a microscopic three-body reaction model. The reaction model has no free adjustable parameter and applicable to reactions at various deuteron incident energies $E_d$ and with both stable and unstable nuclei. The predicted $σ_d^{\rm R}$ are consistent with those evaluated by a phenomenological optical potential for $E_d\leq 200$ MeV in which the potential has been parametrized. A simple formula of $σ_d^{\rm R}$ up to $E_d=1$ GeV, as a function of $E_d$, the target mass number $A$ and its atomic number $Z$, is given.

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arXiv2016

Consistency between the monopole strength of the Hoyle state determined by structural calculation and that extracted from reaction observables

We analyze the $α$-$^{12}$C inelastic scattering to the $0^+_2$ state of $^{12}$C, the Hoyle state, in a fully microscopic framework. With no free adjustable parameter, the inelastic cross sections at forward angles are well reproduced by the microscopic reaction calculation using the transition density of $^{12}$C obtained by the resonating group method and the nucleon-nucleon $g$ matrix interaction developed by the Melbourne group. It is thus shown that the monopole transition strength obtained by the structural calculation is consistent with that extracted from the reaction observable, suggesting no missing monopole strength of the Hoyle state.

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arXiv2015

Asymmetry of the parallel momentum distribution of (p,pN) reaction residues

The parallel momentum distribution (PMD) of the residual nuclei of the 14O(p,pn)13O and 14O(p,2p)13N reactions at 100 and 200 MeV/nucleon in inverse kinematics is investigated with the framework of the distorted wave impulse approximation. The PMD shows an asymmetric shape characterized by a steep fall-off on the high momentum side and a long-ranged tail on the low momentum side. The former is found to be due to the phase volume effect reflecting the energy and momentum conservation, and the latter is to the momentum shift of the outgoing two nucleons inside an attractive potential caused by the residual nucleus. Dependence of these effects on the nucleon separation energy of the projectile and the incident energy is also discussed.

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arXiv2015

Microscopic coupled-channel calculations of nucleus-nucleus scattering including chiral three-nucleon-force effects

We analyze $^{16}$O-$^{16}$O and $^{12}$C-$^{12}$C scattering with the microscopic coupled-channels method and investigate the coupled-channels and three-nucleon-force (3NF) effects on elastic and inelastic cross sections. In the microscopic coupled-channels calculation, the Melbourne g-matrix interaction modified according to the chiral 3NF effects is used. It is found that the coupled-channels and 3NF effects additively change both the elastic and inelastic cross sections. As a result, the coupled-channels calculation including the 3NF effects significantly improves the agreement between the theoretical results and the experimental data. The incident-energy dependence of the coupled-channels and 3NF effects is also discussed.

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arXiv2015

Microscopic calculations based on chiral two- and three-nucleon forces for proton- and $^{4}$He-nucleus scattering

We investigate the effects of chiral three-nucleon force (3NF) on proton scattering at 65 MeV and $^{4}$He scattering at 72 MeV/nucleon from heavier targets, using the standard microscopic framework composed of the Brueckner-Hartree-Fock (BHF) method and the $g$-matrix folding model. For nuclear matter, the $g$ matrix is evaluated from chiral two-nucleon force (2NF) of N$^{3}$LO and chiral 3NF of NNLO by using the BHF method. Since the $g$ matrix thus obtained is numerical and nonlocal, an optimum local form is determined from the on-shell and near-on-shell components of $g$ matrix that are important for elastic scattering. For elastic scattering, the optical potentials are calculated by folding the local chiral $g$ matrix with projectile and target densities. This microscopic framework reproduces the experimental data without introducing any adjustable parameter. Chiral-3NF effects are small for proton scattering, but sizable for $^{4}$He scattering at middle angles where the data are available. Chiral 3NF, mainly in the 2$π$-exchange diagram, makes the folding potential less attractive and more absorptive for all the scattering.

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arXiv2015

A microscopic approach to $^{3}$He scattering

We propose a practical folding model to describe $^{3}$He elastic scattering. In the model, $^{3}$He optical potentials are constructed by making the folding procedure twice. First the nucleon-target potential is evaluated by folding the Melbourne $g$-matrix with the target density and localizing the nonlocal folding potential with the Brieva--Rook method, and second the resulting local nucleon-target potential is folded with the $^{3}$He density. This double single-folding model well describes $^{3}$He elastic scattering from $^{58}$Ni and $^{208}$Pb targets in a wide incident-energy range from 30 MeV/nucleon to 150 MeV/nucleon with no adjustable parameter. Spin-orbit force effects on differential cross sections are found to be appreciable only at higher incident energies such as 150 MeV/nucleon. Three-nucleon breakup effects of $^{3}$He are investigated with the continuum discretized coupled-channels method and are found to be appreciable only at lower incident energies around 40 MeV/nucleon. Effects of knock-on exchange processes are also analyzed.

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arXiv2014

Roles of chiral three-nucleon forces in nucleon-nucleus scattering

We investigate the roles of chiral three-nucleon force (3NF) in nucleon-nucleus elastic scattering, using the standard framework based on the Brueckner-Hartree-Fock method for nuclear matter and the $g$-matrix folding model for the nucleon-nucleus scattering. In nuclear matter, chiral 3NF at NNLO level (mainly the 2$π$-exchange diagram) makes the single particle potential less attractive for the singlet-even channel and more absorptive for the triplet channels. The single-particle potential calculated from chiral two-nucleon force (2NF) at N$^{3}$LO level is found to be close to that from Bonn-B 2NF. The Melbourne $g$-matrix interaction is a practical effective interaction constructed by localizing the $g$-matrices calculated from Bonn-B 2NF. We then introduce the chiral-3NF effects to the local Melbourne $g$-matrix interaction. For nucleon-nucleus elastic scattering on various targets at 65 MeV, chiral 3NF makes the folding potential less attractive and more absorptive. The novel property for the imaginary part is originated in the enhancement of tensor correlations due to chiral 3NF. The two effects are small for differential cross sections and vector analyzing powers at the forward and middle angles where the experimental data are available. If backward measurements are done, the data will reveal the effects of chiral 3NF.

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arXiv2014

Extracting electric dipole breakup cross section of one-neutron halo nuclei from breakup observables

How to extract an electric dipole (E1) breakup cross section σ(E1) from one- neutron removal cross sections measured by using 12C and 208Pb targets, σ_(-1n)^C and σ_(-1n)^Pb, respectively, is discussed. It is shown that within about 5% error, σ(E1) can be obtained by subtracting Γσ_(-1n)^C from σ_(- 1n)^Pb, as assumed in preceding studies. However, for the reaction of weakly-bound projectiles, the scaling factor Γis found to be two times as large as that usually adopted. As a result, we obtain 13-20% smaller σ(E1) of 31Ne at 250 MeV/nucleon than extracted in a previous analysis of experimental data. By compiling the values of Γobtained for several projectiles, Γ=(2.30 +/- 0.41)\exp(- S_n)+(2.43 +/- 0.21) is obtained, where S_n is the neutron separation energy. The target mass number dependence of the nuclear parts of the one-neutron removal cross section and the elastic breakup cross section is also investigated.

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arXiv2014

Effects of a chiral three-nucleon force on nucleus-nucleus scattering

We investigate the effects of chiral NNLO three-nucleon force (3NF) on nucleus-nucleus elastic scattering, using a standard prescription based on the Brueckner-Hartree-Fock method and the g-matrix folding model. The g-matrix calculated in nuclear matter from the chiral N3LO two-nucleon forces (2NF) is close to that from the Bonn-B 2NF. Because the Melbourne group have already developed a practical g-matrix interaction by localizing the nonlocal g-matrix calculated from the Bonn-B 2NF, we consider the effects of chiral 3NF, in this first attempt to study the 3NF effects, by modifying the local Melbourne g-matrix according to the difference between the g-matrices of the chiral 2NF and 2NF+3NF. For nucleus-nucleus elastic scattering, the 3NF corrections make the folding potential less attractive and more absorptive. The latter novel effect is due to the enhanced tensor correlations in triplet channels. These changes reduce the differential cross section at the middle and large angles, improving the agreement with the experimental data for 16O-16O scattering at 70 MeV/nucleon and 12C-12C scattering at 85 MeV/nucleon.

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arXiv2014

Microscopic optical potentials for $^4$He scattering

We present a reliable double-folding (DF) model for $^{4}$He-nucleus scattering, using the Melbourne $g$-matrix nucleon-nucleon interaction that explains nucleon-nucleus scattering with no adjustable parameter. In the DF model, only the target density is taken as the local density in the Melbourne $g$-matrix. For $^{4}$He elastic scattering from $^{58}$Ni and $^{208}$Pb targets in a wide range of incident energies from 20~MeV/nucleon to 200~MeV/nucleon, the DF model with the target-density approximation (TDA) yields much better agreement with the experimental data than the usual DF model with the frozen-density approximation in which the sum of projectile and target densities is taken as the local density. We also discuss the relation between the DF model with the TDA and the conventional folding model in which the nucleon-nucleus potential is folded with the $^{4}$He density.

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arXiv2014

Ground-state properties of neutron-rich Mg isotopes

We analyze recently-measured total reaction cross sections for 24-38Mg isotopes incident on 12C targets at 240 MeV/nucleon by using the folding model and antisymmetrized molecular dynamics(AMD). The folding model well reproduces the measured reaction cross sections, when the projectile densities are evaluated by the deformed Woods-Saxon (def-WS) model with AMD deformation. Matter radii of 24-38Mg are then deduced from the measured reaction cross sections by fine-tuning the parameters of the def-WS model. The deduced matter radii are largely enhanced by nuclear deformation. Fully-microscopic AMD calculations with no free parameter well reproduce the deduced matter radii for 24-36Mg, but still considerably underestimate them for 37,38Mg. The large matter radii suggest that 37,38Mg are candidates for deformed halo nucleus. AMD also reproduces other existing measured ground-state properties (spin-parity, total binding energy, and one-neutron separation energy) of Mg isotopes. Neutron-number (N) dependence of deformation parameter is predicted by AMD. Large deformation is seen from 31Mg with N = 19 to a drip-line nucleus 40Mg with N = 28, indicating that both the N = 20 and 28 magicities disappear. N dependence of neutron skin thickness is also predicted by AMD.

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arXiv2013

Mass-number and isotope dependence of the local microscopic optical potential for polarized proton scattering

We derive local microscopic optical potentials $U$ systematically for polarized proton scattering at 65~MeV using the local-potential version of the Melbourne $g$-matrix folding model. As target nuclei, we take $^{6}$He and neutron-rich Ne isotopes in addition to stable nuclei of mass number $A=4$--$208$ in order to clarify mass-number and isotope dependence of $U$. The local potentials reproduce the experimental data systematically and have geometries similar to the phenomenological optical potentials for stable targets. The target density is broadened by the weak-binding nature and/or deformation of unstable nuclei. For the real spin-orbit part of $U$ the density broadening weakens the strength and enlarges the radius, whereas for the central part it enlarges both of the strength and the radius. The density-broadening effect is conspicuous for halo nuclei such as $^{6}$He and $^{31}$Ne. Similar discussions are made briefly for proton scattering at 200~MeV. We briefly investigate how the isovector and the non spherical components of $U$ affect proton scattering.

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arXiv2013

Two neutron decay from the $2_1^+$ state of $^6$He

Decay mode of the $2_1^+$ resonant state of $^6$He populated by the $^6$He breakup reaction by $^{12}$C at 240 MeV/nucleon is investigated. The continuum-discretized coupled-channels method is adopted to describe the formation of the $2_1^+$ state, whereas its decay is described by the complex-scaled solutions of the Lippmann-Schwinger equation. From analysis of invariant mass spectra with respect to the $α$-$n$ and $n$-$n$ subsystems, coexistence of two decay modes is found. One is the simultaneous decay of two neutrons correlating with each other and the other is the emission of two neutrons to the opposite directions. The latter is found to be free from the final state interaction and suggests existence of a di-neutron in the $2_1^+$ state of $^6$He.

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arXiv2013

Reaction mechanism in odd-even staggering of reaction cross sections

It was recently suggested that the odd-even staggering of reaction cross sections is an evidence of the pair- ing anti-halo effect on projectile radii. We define the dimensionless staggering parameters, Γrds and ΓR, for projectile radii and reaction cross sections, respectively, and analyze the relation between Γrds and ΓR for the scattering of 14,15,16C from a 12C target at 83 MeV/A by taking account of projectile-breakup and nuclear- medium effects newly with the microscopic version of the continuum discretized coupled-channels method. The value of ΓR is deviated from that of Γrds by the projectile-breakup effect, the nuclear-medium effect and an effect due to the fact that the scattering are not the black-sphere scattering (BSS) exactly. The projectile-breakup and nuclear medium effects are nearly canceled for ΓR. The remaining non-BSS effect becomes small as an incident energy decreases, indicating that nucleus-nucleus scattering at lower incident energies are a good probe of evaluating Γrds from measured reaction cross sections.

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