R.J. Griffiths

Phenomenological and microscopic optical potentials for 88 MeV 7Li scattering

The elastic scattering cross sections for 88 MeV 7Li ions have been measured for targets of 24,26Mg and 40,48Ca. Analyses using both phenomenological and microscopic optical potentials provide information on the energy dependence of optical parameters, and the extent to which the potentials are determined for these light ions. The use of a double-folding microscopic model demonstrates the need for normalisation of the real potential by a factor of 0.5 in contrast to measurements at lower energies. The contribution of exchange effects density dependence and break-up are discussed.

Elastic scattering of 33 MeV tritons and isospin dependence of mass-3 optical potential

Abstract Differential cross section data are presented for the elastic scattering of 33 MeV tritons from a range of nuclei from 12 C to 232 Th. These data have been analysed using a phenomenological optical model. Parameters are presented for three families of the real potential. A comparison of the triton optical model potential with those from a re-analysis of 3 He scattering from fp shell nuclei has allowed the isospin dependence of the optical model potential for mass-3 projectiles to be obtained in this mass region.

An analysis of polarization and cross-section data for the p-3He system at 30 and 50 MeV

Abstract Differential cross-section and polarization measurements on the p- 3 He system at 30 and 50 MeV have been analysed in terms of real phase shifts. It is shown that there is not sufficient data at either energy to define a unique solution.

Coupled channels description of single and mutual excitation in the scattering of 7Li from 12C and 24, 26Mg

Abstract Coupled channels calculations have been made for the scattering of 7Li from 12C at 63 and 79 MeV and from 24,26Mg at 88 MeV. The calculations describe, simultaneously, the elastic scattering, excitation of 7Li to the 478 keV 1 2 − state, excitation of the target to its first 2+ state, and the mutual excitation of both projectile and target to their 1 2 − and 2+ states respectively. The potentials have been calculated by a double folding model using the M3Y effective interaction for the real part, and a gaussian effective interaction for the imaginary part. Realistic densities have been used for the ground states of 7Li, 12C and 24, 26Mg and also the transition densities to the excited states using a microscopic plus macroscopic prescription. For the mutual excitation, both one-step processes with l = 0, 2 and 4 and two-step processes were included. The calculations show that the two-step processes are the dominant contribution to the mutual excitation, but at forward angles, the oscillations in the data are only reproduced with the coherent addition of the one-step processes, which are dominated by the l = 4 contribution. Even when coupling to all single and mutual excitations are included the real potential still requires a normalization of about 0.6. The addition of the quadrupole re-orientation matrix element for the ground state does not significantly change this value. These calculations confirm that the coupling to the first excited inelastic levels of target and ejectile is not the source of the anomalous M3Y normalization, and that the dominant mode for mutual excitation is a two-step process. However, direct one-step mutual excitation is important for small angles (θ ≲ 20°).

The shape of the helion spin-orbit potential

The detailed shape of the spin-orbit potential needed for helion optical potentials has been determined by measurements with a polarized helion beam. The polarizations produced in the elastic scattering of helions from 26Mg have been measured at 33.4 MeV. The observed polarizations, in conjunction with the elastic differential cross sections, have been analysed using a phenomenological optical models. The geometry of the spin-orbit potential is well determined and is characterized by radius and diffuseness parameters considerably smaller than those of both the real and imaginary potentials. This means that the convention of using the same geometry for the real spin-orbit potentials is no longer acceptable and the use of simple folding models for helion spin-orbit potentials is not justified.

36 MeV triton inelastic scattering and one-nucleon transfer reactions

Abstract Differential cross sections have been obtained for inelastic scattering and one nucleon transfers on targets of 28,30 Si and 26 Mg using a 36 MeV beam of tritons. CCBA and DWBA fits have been applied to these data and the deformation parameters and spectroscopic factors obtained compared to previous measurements and shell model predictions. Comparisons are made of the fits obtained with zero-range, local energy approximation and exact finite range calculations. High energy tritons are shown to be a precise and valuable spectroscopic tool.

Elastic scattering of 36 MeV tritons

36 MeV triton elastic scattering data have been obtained for targets of 30Si, 28Si, 26Mg, 16O and 12C. These data are analysed in terms of a conventional phenomenological optical model and double-folding optical model.

The effects of finite range and channel coupling in the 32S(3He, 4He)31S reaction

Abstract Comparisons of exact finite-range (EFR) DWBA calculations and zero-range (ZR) calculations are presented for the cross sections and analysing powers of the 32 S ( 3 He , 4 He ) 31 S reaction to the ground state ( 1 2 + ), 1.25 MeV ( 3 2 + ) and 2.23 MeV ( 5 2 + ) states. The data for the 3 2 + and 5 2 + states are quite well fitted and show the characteristic j-dependence of the analysing powers. Only small differences between the EFR and ZR calculations are seen. The analysing power data for the 1 2 ± state are poorly fitted by the EFR or ZR calculations but better agreement is obtained when the coupling to other levels is included in a coupled channel Born approximation (CCBA) calculation.

The 40,44,48Ca(3He, 3He) and (3He, 4He) reactions at 50 MeV

Measurements have been made of the (3He, 3He) and (3He, 4He) reactions on the isotopes of calcium 40Ca, 44Ca and 48Ca at a energy of 50.4 MeV. The results have been analysed with conventional optical potentials and DWBA. The adequacy of the former and inadequacy of the latter for reactions with composite particles are discussed.

The interaction of helium ions with 56Fe near 83 MeV

The 56Fe(3He,4He) reaction has been measured at 83 MeV together with the elastic scattering for the 3He at 83 MeV and 4He at 86 MeV. The 3He scattering produced a unique optical potential when analysed with a six parameter model but contrasts with the analysis of the 4He scattering for which two acceptable optical potentials were found. The energy dependence of the 3He optical model potential cannot be accommodation over a wide range by a fixed geometry analysis. The limitations of DWBA under angular momentum mismatch conditions for the (3He,4He) reaction are discussed.