R.C. Johnson

Projectile excitation and structure effects in 6Li and 7Li scattering

Abstract Polarized 6, 7 Li scattering from 58 Ni at E c.m. = 13–20 MeV is investigated by coupled-channels calculations including projectile excitation channels. Potentials are obtained by a single-folding procedure assuming an α+d(t) cluster structure for the projectile. All the available data are reproduced by the calculations. Projectile excitation is found to be the dominant effect in the vector analysing power ( iT 11 ) for elastic scattering. These effects are in the opposite directions for 6 Li and 7 Li and explain the opposite signs of the measured iT 11 in the two scatterings. The folding-model tensor potential, which is sensitive to the deformation of the projectile, is mainly responsible for the behaviour of the elastic-scattering tensor analysing power. The cluster-model wave functions used in the folding procedure reproduce the measured Q -moments. The Q -moments of both Li isotopes are negative, but the measured tensor analysing powers ( T T 20 have opposite signs. This can be understood in terms of the different surface structure of 6 Li and 7 Li. Results and discussions for inelastic scattering and for other scattering systems are also given.

Core excitation in one neutron halo systems

Abstract Coupled channel calculations are performed for one neutron halo nuclei using a rotational model for the core structure. A deformed Woods-Saxon potential is used for the neutron-core interaction, where the deformation parameter is estimated using the quadrupole moment of the core and the charge to mass deformation ratio given by shell model calculations. Mean square radii and B (E1) transitions from the first excited state to the ground state in 11 Be are presented and good agreement with experiment is found. The same calculations were performed for 13 C but the agreement with experiment was not as good. Phase shifts for low energy neutrons on 10 Be and 12 C are calculated and we determine positions and widths of resonances. Predictions for the continuum only partly agree with the experimental spectrum. We also calculate the B (E1) distribution of 11 Be for transitions from the ground state to the continuum and these agree with recent coulomb dissociation data. Following the controversy generated by the experimental results for the ground state in 10 Li, we apply our method to investigate the structure of this nucleus.

Symmetry properties of the scattering amplitude and the spin dependence of the deuteron-nucleus interaction

Abstract The implications of rotation, time reversal and reflection invariance for the elastic scattering of a spin- s particle by a spin-zero particle are discussed in terms of the properties of the scattering amplitude. It is shown how these properties can be used to suggest experiments with polarized deuterons that are expected to be particularly sensitive to the presence of 2nd-rank tensor forces.

Core excitation in three-body systems: Application to 12Be

Abstract Core excitation is included in the three-body hyperspherical formulation for systems of the type (core + n + n). We show that core excitation generates a three-body attraction, improving on the common underbinding problem present in many inert-core models. The Pauli principle significantly influences both the binding energies and the wave functions. A study of the effect of the different terms of the nn interaction on the three-body system is presented. The model is applied to 12Be, where one would expect that the inert-core approximation would not be appropriate. A deformed n-core interaction is determined by the properties of the subsystem 11Be. Results for the binding energy, r.m.s. radius, structure and momentum distribution of the ground state of 12Be are presented, and very good agreement with experimental data is found. A full comparison with the inert-core model is made. The results with core excitation show a very small component of ( p 1 2 )2 neutrons in the ground-state wave function, in contrast to the inert-core model where the 12Be ground state is mainly ( p 1 2 )2 neutrons relative to the core. We point out the possible implications of this fact for heavier Be isotopes, especially 13Be. The spectrum of 12Be bound excited states is calculated and compared with the measured values and some discrepancies are found. Following a recent proposal for an experiment, predictions for the 12Be(p,d) transfer cross sections are given.

The effect of the D-state of the deuteron in (d, p) and (p, d) reactions

Abstract The effect of the D-state of the deuteron in (d, p) and (p, d) reactions is discussed within the framework of the distorted waves Born approximation. Numerical estimates with plane waves are used to suggest that the D-state may play an important role in certain reactions. The necessary modifications of previous work on polarization effects in the distorted waves theory are discussed in detail.

Four-body continuum-discretized coupled-channels calculations using a transformed harmonic oscillator basis

The scattering of a weakly bound three-body system by a target is discussed. A transformed harmonic oscillator basis is used to provide an appropriate discrete and finite basis for treating the continuum part of the spectrum of the projectile. The continuum-discretized coupled-channels framework is used for the scattering calculations. The formalism is applied to different reactions, {sup 6}He+{sup 12}C at 229.8 MeV, {sup 6}He+{sup 64}Zn at 10 and 13.6 MeV, and {sup 6}He+{sup 208}Pb at 22 MeV, induced by the Borromean nucleus {sup 6}He. Both the Coulomb and nuclear interactions with a target are taken into account.

Vector and tensor analysing power of (d, p) reactions and deuteron D-state effects

Abstract The vector and tensor analysing power was measured for (d, p) reactions on 9 Be, 12 C, 16 O, 19 F, 25 Mg, 28 Si and 40 Ca for lab reaction angles from 0° to 50° at 12.3 MeV incident deuteron energy. Fifteen transitions were studied including orbital angular momentum transfers l n = 0,1,2, 3. The experimental results were analysed in terms of distorted-wave theory including deuteron D-state effects. The calculations show that the deuteron D-state cannot be ignored in the description of the tensor analysing power. The j -dependence of D-state effects is discussed.

Energy dependence of alpha-particle and heavy-ion optical potentials

Abstract It is shown that the observed energy dependence of α-particle optical potentials can be understood in microscopic terms. General results which can be applied to other composite projectiles are obtained.

Projectile excitation effects on vector polarized 6Li scattering from 28Si and 16O

Abstract Scattering of polarized 6 Li from 28 Si and 16 O targets at E lab ∼ 20 MeV is investigated including the effects of projectile excitation. A single folding model, assuming a d + α cluster structure for 6 Li, was used consistently for the interactions in the coupled channels calculations. Contrary to existing one-channel calculations the vector analysing powers were found to be generated by the projectile excitation mechanism and not the folding model spin-orbit potential.

Tensor interaction in heavy-ion scattering: (I). The turning-point model

Abstract The Heidelberg shape-effect model for heavy-ion tensor interactions is reformulated and generalized using the Hooton-Johnson formulation. The generalized semiclassical model (the turning-point model) predicts that the components of the tensor analysing power T 2q have certain relations with each other for each type of tensor interaction ( T R , T P and T L types). The predicted relations between the T 2q are very simple and have a direct connection with the properties of the tensor interaction at the turning point. The model predictions are satisfied in quantum-mechanical calculations for 7 Li and 23 Na elastic scattering from 58 Ni in the Fresnel-diffraction energy region. As a consequence of this model, it becomes possible to single out effects from a T P − or T L -type tensor interaction in polarized heavy-ion scattering. The presence of a T P -type tensor interaction is suggested by measured T 20 / T 22 ratios for 7 Li+ 58 Ni scattering. In the turning-point model the three types of tensor operator are not independent, and this is found to be true also in a quantum-mechanical calculation. The model also predicts relations between the components of higher-rank tensor analysing power in the presence of a higher-rank tensor interaction. The rank-3 tensor case is discussed in detail.