J.A.R. Griffith

Polarization in the elastic scattering of 12 MeV deuterons

Abstract Angular distributions are presented of the vector polarization of 12 MeV deuterons elastically scattered by Si, 52 Cr, 56 Fe, 58 Ni, 93 Nb, Ag and In. Large values of polarization were observed for Si, 52 Cr, 56 Fe and 58 Ni. The polarization diffraction pattern was seen to decrease systematically with Z up to silver but was found to increase for indium. The measurements were analysed in terms of an optical model which accounted for most of the results including those of Ag and In. Average sets of optical-model parameters have been found. The A and Z dependence of some parameters have been investigated.

Elastic and inelastic scattering of vector polarized deuterons by Fe and Ni isotopes

Abstract Vector analysing powers and cross sections for deuteron elastic and inelastic scattering by 54, 56, 58 Fe and 60 Ni were measured at a deuteron energy of 12.3 MeV. Large changes in the elastic scattering analysing power were observed for small changes in the target mass. The elastic data are well described by standard optical model calculations employing fixed real and spin-orbit geometry parameters. The analysis yielded a spin-orbit potential depth of about 6.5 MeV and a volume integral of the real central potential of about 365 MeV · fm 3 per nucleon for each nucleus. The variations of the measured analysing powers with the target nucleus are explicable in terms of a dependence of the strength of the imaginary potential upon the neutron excess ( N - Z )/ A . The data for the 2 + first-excited states are adequately described by a collective model analysis using both DWBA and coupled-channels formalisms. The coupled-channels treatment revealed a strong dependence of the predicted elastic and inelastic analysing powers on the mode of excitation and the magnitude of the deformation parameter.

Polarization of 17.8 MeV protons elastically scattered by nuclei

Abstract Angular distributions are presented for the polarization of 17.8 MeV protons elastically scattered by Be, S, Fe, Co, Cu, Zn, Ga, Ag and In at angles between 25° and 120° (lab). Targets of natural isotopic abundance were used and the experimental technique involved the single scattering of a totally polarized proton beam obtained by bombarding gaseous hydrogen with 40 MeV alpha particles. These results, together with the differential cross-section data and previous results for Si, Ca, 58 Ni 60 Ni and Mo, were analysed using an optical model automatic search programme. The geometrical parameters were fixed and systematic trends in the real central, imaginary central and spin-orbit potentials were investigated. Improved fits were obtained by reducing the radius of the spin-orbit potential with respect to the radius of the central potential.

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.

Stripping reactions and elastic scattering of 12 MeV vector polarized deuterons on 9Be and 12C

Abstract Angular distributions were obtained of the vector analysing power for 9 Be(d, d), 12 C(d, d), 9 Be(d, p) 10 Be and 12 C(d, p) 13 C reactions induced by 12 MeV polarized deuterons. Most features of the (d, p) reactions were adequately accounted for by DWBA calculations with optical-model deuteron potentials which described the elastic scattering at the same energy. The calculations distinctly favoured real central deuteron potentials around 100 MeV.

Vector analysing power of the (d, p) reaction on 28Si, 52Cr and 88Sr AT 12 MeV

Abstract The vector analysing power of the (d, p) reaction leading to several states of the final nuclei 29 Si, 53 Cr and 89 Sr was measured using a 12.3 MeV vector polarized deuteron beam. The data exhibit a distinct j -dependence which is in accordance with known spin and parity assignments of the final states. Present experimental results are compared with existing measurements of proton polarization. An extensive DWBA analysis confirms an applicability of the method for calculating the vector analysing power for most reactions involving orbital momentum transfer l = 1, 2, 3. It is less satisfactory in cases with l = 0. The effects of optical model parameters and particularly the spin-orbit distortion in the deuteron and proton channel are discussed.

Polarization in the elastic scattering of 12 MeV deuterons by 12C, 56Fe and 58Ni

Abstract Angular distributions are presented of the vector polarization of 12 MeV deuterons elastically scattered by 12C, 56Fe and 58Ni for lab scattering angles 20–160°. The vector polarized deuteron beam from the Birmingham Radial Ridge Cyclotron polarized deuteron source was used, and the experimental method involved frequent “on-off” switching of the polarization at the source. Asymmetries were measured, using semiconductor detector telescopes in the scattering plane, against simultaneous readings of a carbon polarimeter whose analysing power was calibrated by means of the d-4He scattering. Large values of polarization were observed for 12C; the medium-weight nuclei 56Fe and 58Ni showed characteristic oscillatory patterns of lower amplitude. An attempt was made to explain the results in terms of optical-model predictions, and the calculations seem to favour a potential for deuterons approximating the sum of the proton and neutron optical model potentials.

Elastic and inelastic scattering of 12 MeV polamzed deuterons by 24Mg

Abstract The vector analysing power was measured for 12.1 MeV deuterons scattered by 24 Mg. Angular distributions are presented for the ground and 1.37 MeV (2 + ) states. The elastic scattering data could not be reproduced satisfactorily by spherical optical-model calculations. Both the DWBA and coupled-channels formalisms yielded an acceptable description of the inelastic scattering data using an average deuteron optical-model potential. Coupled-channels predictions of the elastic scattering vector analysing power revealed strong dependence on the mode of excitation and the deformation parameter while an addition of spin-orbit coupling had little effect on the calculated results.

Polarization effects in deuteron stripping reactions on 207Pb and 208Pb near the Coulomb barrier

Abstract Angular distributions of the vector analysing power of the reactions 207 Pb(d, p) 208 Pb(g.s.) and 208 Pb(d, p) 208 Pb (0.0,1.57,2.03, 2.49+2.54 MeV) were measured at 12.3 MeV. Distorted-waves calculations were performed, yielding information on choice of the distorting potentials and the reliability of extraction of spectroscopic factors. Most features of the reactions including the polarizations can be adequately accounted for by the conventional distorted-wave theory using potentials which describe best the elastic scattering and for most of the transitions observed, the agreement is excellent. In the region dominated by Coulomb distortions the sign of polarization is simply related to the spin changes involved in the reaction. Present results indicate that the polarization is negative or positive over most of the angular range depending on whether the orbital angular momentum and spin of the captured neutron are parallel or anti-parallel ( j = l± 1 2 ), in agreement with distorted-wave theory.

Tensor analysing powers in deuteron elastic scattering by 50Cr, 66Zn and 67Zn

Abstract Vector and tensor analysing powers were measured in deuteron elastic scattering on 50Cr, 66Zn and 67Zn at 12.4 MeV incident deuteron energy. High-accuracy data for T22 show a characteristic dip at ≈ 30° (c.m.) observed on all three nuclei. A phenomenological optical-model analysis has reproduced this feature when a tensor term tR, treated exactly by the programme, was present in the optical potential. Comparable fits to the data have been achieved when the spin-dependent terms of the potential were derived from the deuteron folding model. It is suggested that the deuteron D-state is responsible for the observed behaviour of T22 in elastic scattering at forward angles.