Y. Sakuragi

Tensor interactions and polarization phenomena in heavy-ion scattering

Abstract Elastic and inelastic scattering of 7Li by 58Ni at Elab = 14.2 and 20.3 MeV is investigated theoretically, special emphasis being laid on polarization phenomena. A parameter-independent study shows second-rank tensor interactions to be the main origin of tensor analyzing powers for both elastic and inelastic scattering. Coupled-channel (CC) calculations using cluster-folding interactions which include the tensor terms are found to be successful in reproducing the data for cross sections and vector and tensor analyzing powers, when projectile excitation effects are sufficiently taken into account. Scattering of 6Li by 58Ni at Elab = 20.0 MeV is also investigated by the CC calculation, where successes similar to the 7Li case are obtained in understanding experimental data.

Halo structure and soft dipole mode of the 6He nucleus in the α + n + n cluster model

Abstract The ground-state properties and the soft dipole mode of the 6 He nucleus are investigated by the coupled-rearrangement-channel variational method based on an α + n + n cluster model, where the effect of the Pauli principle between the α core and valence neutrons is taken into account. A reasonable binding energy is obtained for the ground state with the use of realistic nn and nα interactions. The resulting ground-state wave function has a long-range tail in the neutron distribution, clearly indicating the neutron halo structure in the 6 He nucleus. The calculated distribution of the electric-dipole transition to the 1 − excited states shows a localization of the strength to a rather broad peak around E x ≃ 2.5 MeV with a width of about 4 MeV.

Effects of projectile breakup and target excitation in scattering of polarized 7Li

Abstract Scattering of polarized 7Li by 12C at Elab = 21 MeV and by 26Mg at Elab = 44 MeV is investigated by the use of the double-folding interaction in the coupled-channel framework where the breakup of 7Li to non-resonant continuum region and the excitation of 12C or 26Mg to the first 2+ state are taken into account in addition to the excitations of 7Li to the discrete levels so far considered. The effective interactions induced by the couplings between these channels are studied in detail by the invariant-amplitude method with fruitful results. For example, serious effects due to the projectile virtual excitation are observed in the central and third-rank tensor interactions in the elastic channel. The calculated cross sections and vector and tensor analyzing powers show overall good agreements with experimental data for the elastic scattering and the inelastic scattering to the 1 2 state of 7Li. The measured inelastic cross sections for the excitation of 26Mg and the mutual excitation to the 1 2 − state of 7Li and the 2+ state of 26Mg for the 7Li+26Mg scattering as well as the excitation of 12C for the 7Li+ 12C scattering are well described by the calculation. The target excitation accompanied by the mutual one and the non-resonant breakup of the projectile newly introduced are found to make important contributions to these physical quantities.

Scattering of polarized 7Li by 120Sn and projectile-target spin-dependent interactions

Abstract Scattering of 7 Li by 120 Sn targets at E lab = 44 MeV is investigated in the coupled-channel frame by taking account of the projectile virtual excitations to the lowest three excited states. Calculations are performed by the cluster-folding (CF) interactions and the double-folding (DF) one. Both interactions reproduce very well the experimental data on the cross section, the vector analyzing power, the second-rank tensor ones and the third-rank tensor one in elastic and projectile inelastic scattering, although some differences are found between the CF results and the DF ones. In the calculation, the virtual excitations of the projectile are important for most of the analyzing powers and the spin-orbit interaction is indispensable for the vector analyzing power. These features are in contrast to those in 7 Li- 58 Ni scattering at 20 MeV and are interpreted as over-Coulomb-barrier effects. The scattering amplitudes and the analyzing powers are investigated by the invariant amplitude method, which provides a key connecting the spin-dependent interactions to the analyzing powers. The method proposes an important relationship between the tensor analyzing powers, which is useful in analyses of both theoretical and experimental results. Finally, it is found that in the elastic scattering the second-rank tensor analyzing powers are proportional to the strength of the second-rank tensor interaction and the vector and third-rank tensor analyzing powers to the square or cube of the strength of this interaction, while in the inelastic scattering the cross section is proportional to the square of the strength of the tensor interaction, other quantities being weakly dependent on the strength.

Folding interactions in the scattering of soft heavy ions by light nuclei

Abstract Scattering of polarized 7 Li by 12 C and polarized 6 Li by 16 O at E lab ∼20 MeV is studied by both cluster folding interactions and double folding ones, where projectile virtual excitation effects are included by the coupled-channel method. The results strongly depend on the choices of interactions and reaction mechanisms reflecting low Coulomb barrier effects.

12C → 3α Breakup effect on the scattering of 16O + 12C and 13C + 12C

Abstract A coupled-channel calculation with microscopic 3α wave functions of the bound, resonant breakup and non-resonant breakup states of 12 C reproduces observed angular distribution of 16 O + 12 C at E( 16 O ) = 168, 216 and 311 MeV and of 13 C + 12 C at E( 13 C ) = 260 MeV . The coupled-channel effects of the breakup states are striking. Dynamical polarization potentials induced by the 12 C excited states are calculated and discussed.

Breakup effect on 6Li-nucleus scattering at intermediate energies

Abstract Elastic scattering of 6 Li by a nucleus at intermediate energies has been investigated by the continuum-discretised coupled-channels method based on a cluster-folding (CF) model of 6 Li-nucleus interactions. The projectile breakup effect, which was quite significant at low energies, has been found to be less important at intermediate energies. This reflects the strong energy dependence of the input optical potentials for α and d clusters. The results suggest the validity of a simple CF model in the description of 6 Li-nucleus scattering at intermediate energies.

Roles of folding spin-orbit potentials in 6,7Li scattering

Abstract Spin-dependent interactions responsible for vector analyzing powers in elastic scattering of 6,7 Li are investigated with a special interest in the competition between folding spin-orbit potentials and higher orders of tensor interactions including projectile virtual excitations. For 150 ≳ E lab ≳ 40 MeV, they are both important. For E lab ≲ 20 MeV, however, the folding spin-orbit potential cannot be effective because the attenuation due to the projectile excitation and/or the Coulomb barrier prevents the projectile from intruding into the spin-orbit effective area.

Anomalous renormalization of cluster-folding interactions for 6Li-nucleus scattering at low energies

Abstract The validity of cluster-folding (CF) interactions for elastic scattering of 6 Li by various nuclei is investigated in the α+d+target three-body model. The 6 Li→α+d breakup process is taken into account in the framework of the continuum-discretized coupled-channels (CDCC). It is shown that, at low energies below E lab A p ≅10 MeV , the real part of the CF potentials has to be reduced by about (40–50)%, even when the resonant and non-resonant breakup channels are explicitly included in the CDCC calculations, while no renormalization is necessary for fits to scattering at higher energies.

Projectile breakup effect in elastic scattering of 9Be

Abstract The projectile breakup effect on the elastic scattering of 9Be has been studied by coupled-channel calculations based on the microscopic cluster-model wave functions for 9Be. It is found that the effect is quite significant and essential to reproduce the elastic scattering at Elab = 158 MeV without introducing any renormalisation factor to the double-folding potential. The dynamical polarisation potential derived clearly shows the repulsive nature of the breakup effect.