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Kazuyuki Ogata

Publications and source records attributed to Kazuyuki Ogata.

90 records · Page 5Linked to original sources
arXiv2012

Interplay between the 0+_2 resonance and the nonresonant continuum of the drip-line two-neutron halo nucleus 22C

The breakup cross section (BUX) of 22C by 12C at 250 MeV/nucleon is evaluated by the continuum-discretized coupled-channels method incorporating the cluster-orbital shell model (COSM) wave functions. Contributions of the low-lying 0+_2 and 2+_1 resonances predicted by COSM to the BUX are investigated. The 2+_1 resonance gives a narrow peak in the BUX, as in usual resonant reactions, whereas the 0+_2 resonant cross section has a peculiar shape due to the coupling to the nonresonant continuum, i.e., the Fano effect. By changing the scattering angle of 22C after the breakup, a variety of shapes of the 0+_2 resonant cross sections is obtained. Mechanism of the appearance of the sizable Fano effect in the breakup of 22C is discussed.

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arXiv2012

Determination of 8B(p,gamma)9C reaction rate from 9C breakup

The astrophysical factor of the 8B(p,gamma)9C at zero energy, S18(0), is determined from three-body model analysis of 9C breakup processes. The elastic breakup 208Pb(9C,p8B)208Pb at 65 MeV/nucleon and the one-proton removal reaction of 9C at 285 MeV/nucleon on C and Al targets are calculated with the continuum-discretized coupled-channels method (CDCC) and the eikonal reaction theory (ERT), respectively. The asymptotic normalization coefficient (ANC) of 9C in the p-8B configuration extracted from the two reactions show good consistency, in contrast to in the previous studies. As a result of the present analysis, S18(0) = 66 \pm 10 eVb is obtained.

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arXiv2012

The continuum discretized coupled-channels method and its applications

This is a review on recent developments of the continuum discretized coupled-channels method (CDCC) and its applications to nuclear physics, cosmology and astrophysics, and nuclear engineering. The theoretical foundation of CDCC is shown, and a microscopic reaction theory for nucleus-nucleus scattering is constructed as an underlying theory of CDCC. CDCC is then extended to treat Coulomb breakup and four-body breakup. We also propose a new theory that makes CDCC applicable to inclusive reactions

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arXiv2012

Deformation of Ne isotopes in the island-of-inversion region

The deformation of Ne isotopes in the island-of-inversion region is determined by the double-folding model with the Melbourne $g$-matrix and the density calculated by the antisymmetrized molecular dynamics (AMD). The double-folding model reproduces, with no adjustable parameter, the measured reaction cross sections for the scattering of $^{28-32}$Ne from $^{12}$C at 240MeV/nucleon. The quadrupole deformation thus determined is around 0.4 in the island-of-inversion region and $^{31}$Ne is a halo nuclei with large deformation. We propose the Woods-Saxon model with a suitably chosen parameterization set and the deformation given by the AMD calculation as a convenient way of simulating the density calculated directly by the AMD. The deformed Woods-Saxon model provides the density with the proper asymptotic form. The pairing effect is investigated, and the importance of the angular momentum projection for obtaining the large deformation in the island-of-inversion region is pointed out.

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arXiv2011

Deformation effect on total reaction cross sections for neutron-rich Ne-isotopes

Isotope-dependence of measured reaction cross sections in scattering of $^{28-32}$Ne isotopes from $^{12}$C target at 240 MeV/nucleon is analyzed by the double-folding model with the Melbourne $g$-matrix. The density of projectile is calculated by the mean-field model with the deformed Wood-Saxon potential. The deformation is evaluated by the antisymmetrized molecular dynamics. The deformation of projectile enhances calculated reaction cross sections to the measured values.

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arXiv2011

Determination of the structure of $^{31}$Ne by full-microscopic framework

We perform the first quantitative analysis of the reaction cross sections of $^{28-32}$Ne by $^{12}$C at 240 MeV/nucleon, using the double-folding model (DFM) with the Melbourne $g$-matrix and the deformed projectile density calculated by the antisymmetrized molecular dynamics (AMD). To describe the tail of the last neutron of $^{31}$Ne, we adopt the resonating group method (RGM) combined with AMD. The theoretical prediction excellently reproduce the measured cross sections of $^{28-32}$Ne with no adjustable parameters. The ground state properties of $^{31}$Ne, i.e., strong deformation and a halo structure with spin-parity $3/2_{}^-$, are clarified.

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arXiv2011

Eikonal Reaction Theory for Neutron-Removal Reaction

We present an accurate method of treating the one-neutron removal reaction at intermediate incident energies induced by both nuclear and Coulomb interactions. In the method, the nuclear and Coulomb breakup processes are consistently treated by the method of continuum discretized coupled channels without making the adiabatic approximation to the Coulomb interaction, so that the removal cross section calculated never diverges. This method is applied to recently measured one-neutron removal cross section for $^{31}$Ne+$^{12}$C scattering at 230 MeV/nucleon and $^{31}$Ne+$^{208}$Pb scattering at 234 MeV/nucleon. The spectroscopic factor and the asymptotic normalization coefficient of the last neutron in $^{31}$Ne are evaluated.

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arXiv2011

Effective radii of deuteron induced reactions

The continuum-discretized coupled-channels method (CDCC) for exclusive reactions and the eikonal reaction theory (ERT) as an extension of CDCC to inclusive reactions are applied to deuteron induced reactions. The CDCC result reproduces experimental data on the reaction cross section for $d+^{58}$Ni scattering at 200 MeV/nucleon and ERT does data on the neutron-stripping cross section for inclusive $^7$Li$(d,n)$ reaction at 40 MeV. For deuteron induced reactions at 200 MeV/nucleon, target-dependence of the reaction, elastic-breakup, nucleon-stripping, nucleon-removal, complete- and incomplete-fusion cross sections is clearly explained by simple formulae. Accuracy of the Glauber model is also investigated.

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arXiv2011

Three-Body Model Analysis of Subbarrier alpha Transfer Reaction

Subbarrier alpha transfer reaction 13C(6Li,d)17O(6.356 MeV, 1/2+) at 3.6 MeV is analyzed with a alpha + d + 13C three-body model, and the asymptotic normalization coefficient (ANC) for alpha + 13C --> 17O(6.356 MeV, 1/2+), which essentially determines the reaction rate of 13C(alpha,n)16O, is extracted. Breakup effects of 6Li in the initial channel and those of 17O in the final channel are investigated with the continuum-discretized coupled-channels method (CDCC). The former is found to have a large back-coupling to the elastic channel, while the latter turns out significantly small. The transfer cross section calculated with Born approximation to the transition operator, including breakup states of 6Li, gives (C_{alpha 13C}{17O*})^2 =1.03 \pm 0.29 fm^{-1}. This result is consistent with the value obtained by the previous DWBA calculation.

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arXiv2011

Three-Body Model Calculation of Spin Distribution in Two-Nucleon Transfer Reaction

The differential cross sections of two-nucleon transfer reactions 238U(18O,16O)240U around 10 MeV per nucleon are calculated by one-step Born-approximation with a 16O+2n+238U three-body model. The three-body wave function in the initial channel is obtained with the continuum-discretized coupled-channels method, and that in the final channel is evaluated with adiabatic approximation. The resulting cross sections have a peak around the grazing angle, and the spin distribution, i.e., the cross section at the peak as a function of the transferred spin, is investigated. The shape of the spin distribution is found not sensitive to the incident energies, optical potentials, and treatment of the breakup channels both in the initial and final states, while it depends on the excitation energy of the residual nucleus 240U. The peak of the spin distribution moves to the large-spin direction as the excitation energy increases. To fulfill the condition that the peak position should not exceeds 10 hbar, which is necessary for the surrogate ratio method to work, it is concluded that the excitation energy of 240U must be less than 10 MeV.

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arXiv2010

Dynamical Relativistic Effects in Breakup Processes of Halo Nuclei

The continuum-discretized coupled-channels (CDCC) method is used to study the breakup of weakly-bound nuclei at intermediate energies collisions. For large impact parameters, the Eikonal CDCC (E-CDCC) method was applied. The effects of Lorentz contraction on the nuclear and Coulomb potentials have been investigated in details. Such effects tend to increase cross sections appreciably. We also show that, for loosely-bound nuclei, the contribution of the so-called close field is small and can be neglected.

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arXiv2009

Quantum three-body calculation of the nonresonant triple-αreaction rate at low temperatures

The triple-αreaction rate is re-evaluated by directly solving the three-body Schrödinger equation. The resonant and nonresonant processes are treated on the same footing using the continuum-discretized coupled-channels method for three-body scattering. Accurate description of the α-αnonresonant states significantly quenches the Coulomb barrier between the two-α's and the third αparticle. Consequently, the α-αnonresonant continuum states below the resonance at 92.04 keV, i.e., the ground state of 8Be, give markedly larger contribution at low temperatures than in foregoing studies. We show that Nomoto's method for three-body nonresonant capture processes, which is adopted in the NACRE compilation and many other studies, is a crude approximation of the accurate quantum three-body model calculation. We find about 20 orders-of-magnitude enhancement of the triple-αreaction rate around 10^7 K compared to the rate of NACRE.

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arXiv2009

Description of Four-Body Breakup Reaction with the Method of Continuum-Discretized Coupled-Channels

We present a method for smoothing discrete breakup $S$-matrix elements calculated by the method of continuum-discretized coupled-channels (CDCC). This smoothing method makes it possible to apply CDCC to four-body breakup reactions. The reliability of the smoothing method is confirmed for two cases, $^{58}$Ni($d$, $p n$) at 80 MeV and the $E1$ transition of $^6$He. We apply CDCC with the smoothing method to $^6$He breakup reaction at 22.5 MeV. Multi-step breakup processes are found to be important.

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arXiv2008

A New Glauber Theory based on Multiple Scattering Theory

Glauber theory for nucleus-nucleus scattering at high incident energies is reformulated so as to become applicable also for the scattering at intermediate energies. We test validity of the eikonal and adiabatic approximations used in the formulation, and discuss the relation between the present theory and the conventional Glauber calculations with either the empirical nucleon-nucleon profile function or the modified one including the in-medium effect.

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arXiv2003

Determination of S17 from Systematic Analysis of 8B Coulomb Dissociation

Systematic analysis of 8B Coulomb dissociation with the Asymptotic Normalization Coefficient (ANC) method is proposed to determine the astrophysical factor S17 accurately. An important advantage of the analysis is that uncertainties of the extracted S17 coming from the use of the ANC method can quantitatively be evaluated, in contrast to previous analyses using the Virtual Photon Theory (VPT). Calculation of measured spectra in dissociation experiments is done by means of the method of Continuum-Discretized Coupled-Channels (CDCC). From the analysis of 58Ni(8B,7Be+p)58Ni at 25.8 MeV, S17=22.83 +/- 0.51(theo) +/- 2.28(expt) (eVb) is obtained; the ANC method turned out to work in this case within 1% of error. Preceding systematic analysis of experimental data at intermediate energies, we propose hybrid (HY) Coupled-Channels (CC) calculation of 8B Coulomb dissociation, which makes numerical calculation much simple, retaining its accuracy. The validity of the HY calculation is tested for 58Ni(8B,7Be+p)58Ni at 240 MeV. The ANC method combined with the HY CC calculation is shown to be a powerful technique to obtain a reliable S17.

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arXiv2003

Determination of $S_{17}$ from systematic analyses on $^8$B Coulomb breakup with the Eikonal-CDCC method

A new version of the method of Continuum-Discretized Coupled-Channels method (CDCC) is proposed, that is, the Eikonal-CDCC method (E-CDCC). The E-CDCC equation, for Coulomb dissociation in particular, can easily and safely be solved, since it is a first-order differential equation and contains no huge angular momentum in contrast to the CDCC one. The scattering amplitude calculated by E-CDCC has a similar form to that by CDCC. Then one can construct hybrid amplitude in an intuitive way, i.e., CDCC amplitude is adopted for a smaller angular momentum $L$ and E-CDCC one for a larger $L$ related to an impact parameter $b$. The hybrid calculation is found to perfectly reproduce the quantum mechanical result for $^{58}$Ni($^8$B,$^7$Be$+p$)$^{58}$Ni at 240 MeV, which shows its applicability to systematic analysis of $^8$B dissociation to extract the astrophysical factor $S_{17}$ with high accuracy.

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arXiv2002

Determination of S17 from 7Be(d,n)8B reaction: CDCC analyses based on three-body model

The astrophysical factor $S_{17}$ for $^7$Be($p,γ$)$^8$B reaction is reliably extracted from the transfer reaction $^7$Be($d,n$)$^8$B at $E=7.5$ MeV with the asymptotic normalization coefficient method. The transfer reaction is accurately analyzed with CDCC based on the three-body model. This analysis is free from uncertainties of the optical potentials having been crucial in the previous DWBA analyses.

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