Tokuo Terasawa

Alpha-particle spectroscopic amplitudes and the SU(3) model.

Abstract Formulas for calculating spectroscopic amplitudes for emission or transfer of α-particles are developed in the framework of the harmonic-oscillator shell model with SU(3) classification. These formulas are applied to some interesting states of 20 Ne, e.g., low-lying (sd) 4 shell-model states, members of the lowest K = 0 − band with SU (3) label (90), and 2khω excited states with SU(3) label (10, 0). Spurious c.m. motion is removed. The formulas are also applied to the ground and some excited states of 16 O. The 16 O wave functions of Brown and Green are used in an investigation of how the mixing among 0p-0h, 2p-2h, and 4p-4h states affects the wave function for relative motion between the α-cluster and the mass-12 nucleus. These calculations indicate much larger α reduced widths for states which are mainly 4p-4h than for states which are mainly 0p-0h or 2p-2h. Spectroscopic amplitudes are also calculated for some 16 O and 12 C states described as linear chains of α-particles.

A dynamic polarization potential for heavy-ion scattering

Abstract The effects of target and/or projectile excitation on the elastic scattering of heavy ions are studied. The results are cast in the form of contributions to both the real and imaginary parts of the ion-ion optical potential. In particular, a trivially “equivalent” local potential (TELP) is found to simulate the effects of coupling to one or more open channels. Particular application is made to the dynamic polarization resulting from the long-range Coulomb potential. Comparison with coupled-channel calculations shows that the TELP can accurately reproduce these effects of Coulomb excitation. The correction to the absorptive potential is found to be much larger than that for the real potential. This correction is long-ranged and cannot be simulated by any reasonable adjustment of the usual Woods-Saxon form of potential. The TELP provides an alternative to performing coupled-channels calculations and may be particularly useful when reactions other than inelastic scattering are to be studied.

Spin-Orbit Splitting and Tensor Force. II

The second-order effect of the tensor force on spinorbit splitting In light nuclei through the perturbation theoretic treatment was calculated, using the mesontheoretic potential of Serber, It was found that half the experimental value of the P-state doublet splittirg in He5or N15 is explained through this calculation. Previous calculations have lead to splittings of the wrong sign or of too small a magnitude, while Feingolds variatioral calculation gave toe small a magnitude with the right sign. The comparison of this calculation with Feingolds is discussed. Further results will be reported along with the effects of the tensor forces on O17 and Ca41.

Scattering of nucleons by 12C and the structures of 13N and 13C

Abstract Scattering of protons and neutrons by 12 C have been investigated by the coupled-channel method in collective models for the 12 C nucleus, paying particular attention to their resonance features. Weak spin-spin and l 2 dependent interactions have been taken into account as the correction to the optical potential in the nuclear model. We calculated phase shifts, cross sections and polarizations of elastic scattering for both the proton and the neutron, and total cross sections of inelastic scattering to the 12 C★(2 + , 4.43 MeV) state for the proton, up to E p = 8 MeV and E n = 4 MeV. The rotational model with large deformation of negative sign successfully reproduces experimental data but the vibrational model does not.

Direct and compound processes in nuclear reactions

Abstract The elastic and inelastic scattering of nucleons by nuclei are investigated taking account of the direct and compound processes. First, we choose a few channels which are strongly coupled to the entrance channel and introduce a potential matrix, which describes the interaction among chosen channels and the distortion of the wave in each channel. Then the transition matrix element is written as a sum of two contributions, one from the direct process and the other from the compound process. The average cross section is also divided into two parts, and the interference term vanishes by a suitable choice of the potential matrix. The cross section of the direct process has a stronger energy dependence than the single particle resonance behaviour. The compound cross section, which is the contribution from nearby levels and can be calculated if the potential matrix is known, is shown to have the form of the conventional statistical model with a modified definition of the transmission factor.

Elastic scattering of α-particles by 12C and the structure of 16O

Abstract Scattering of α-particles by 12 C has been investigated by the coupled-channel method in the weak-coupling model of the α-particle and 12 C nucleus. For 12 C the rotational model is adopted and the α-particle is simply treated as a point particle. Spin and angular momentum dependent interactions have been taken into account as a correction to the α- 12 C potential. We calculated the energies and widths of the resonance levels, the energies of the two bound states, the phase shifts, the excitation functions and the angular distributions of the differential cross sections, up to E α = 8 MeV. The experimental data are reasonably well reproduced. The deformation parameter of the α- 12 C potential is considerably different from that of the nucleon- 12 C potential. The reason for this difference is discussed.

The Imaginary Part of Channel-Coupling Potentials for 6Li-Induced Reactions

A microscopic estimate of imaginary coupling potentials used in coupled-channels calculations is performed for the 6Li+,oCa and 6Li+ Pb system in the framework of the Feshbach formalism. Two-step contributions to the imaginary potentials are calculated by taking account of the excitation of the target collective states in the intermediate states. The estimated strength of the potential is found to be too small by a factor of about 3 in comparison with the phenomenological one used in the microscopic coupled-channels analyses of 6Li scattering data by Sakuragi et a!.