J.B.A. England

The hydrogen and oxygen content of self-supporting carbon foils prepared bydc glow discharge in ethylene

Abstract The hydrogen and oxygen content of self-supporting carbon films produced bydc glow discharge have been determined using a precise method involving the elastic scattering of 25 MeV α-particles. The number of carbon-hydrogen bonds has been determined for similar samples using infra-red spectroscopy. The results are compared with those for samples made by the carbon arc process. Assuming that the glow discharge carbon contains graphitic regions surrounded by amorphous tetrahedrally bonded material to which hydrogen can attach, a simple estimate is made of the relative numbers of carbon atoms in the two forms.

The elastic scattering of 33 MeV polarized 3He particles by beryllium and carbon

Abstract Angular distributions of 3 He polarization in elastic scattering from 9 Be and 12 C, and in inelastic scattering to the 4.44 MeV state of 12 C were measured using a 33 MeV polarized 3 He beam. The polarization and cross-section data were successfully analysed in terms of the standard optical model. Selectively of the 3 He elastic polarization for various potential sets was established in both optical model and coupled-channel analyses. While it is possible to determine unambiguously the geometry of the spin-orbit term, its strength is strongly correlated with other optical model parameters.

The elastic scattering of 33 MeV 3He particles from 58,60,62,64Ni, 63,65Cu and 64,66,68Zn

Abstract Differential cross sections have been measured for the elastic scattering of 33 MeV 3 He particles from targets of 58,60,62,64 Ni, 63,65 Cu and 64,66,68 Zn over the angular range 5° to 175°. The data have been analysed with the optical model, with particular emphasis on the investigation of the ambiguities in the real potential, the form of the imaginary potential and the use of a spin-orbit term.

The elastic scattering of 25MeV α-particles and neutron shell effects in the A = 50 TO A = 93 mass region

Abstract Experimental elastic scattering angular distributions of 25 MeV α-particles scattered from 28 nuclei ranging from 50Cr to 93Nb have been measured and then analysed in terms of a regular optical model with standard Woods-Saxon geometries for both the real and imaginary potentials. The experimental distributions are well fitted over the whole angular range from 5° to 175° c.m. by the predictions, provided that a smaller than normal diffuseness is used for the imaginary potentials. The usual families of potentials with volume integrals differing by approximately 100 MeV · fm3 are found. The family with volume integral ranging from 540 to 420 MeV· fm3 over the nuclei studied has been chosen as the most appropriate, corresponding to the single family found for α-particle elastic scattering at above 100 MeV. When plotted as functions of the back-angle enhancement parameter γ(θ), the derived parameter at the strong absorption radius, vsar, shows clear grouping into nuclei with similar neutron shell configurations. The derived optical model rms radii also show an abrupt change at the N = 40 neutron sub-shell closure. These effects are shown to be consistent with a contribution to the α-nucleus potential from the neutron pairing interaction.

The j-dependence of (3He, d) and (3He, α) reaction analysing powers in the 1p shell

One of the most important experimental results from polarized deuteron studies is the ability to obtain reliable spectroscopic information from measurements of the vector analysin power in transfer reactions. With the availability of a polarized He beam it is of consid- erable interest to determine whether a similar j-dependence of the 3He analysing power exists. Cross section measurements in the 30 MeV region have shown that the (3He,d) and (3He,α) reactions can be quantitatively described by direct reaction theories. Therefore, j-dependence could provide a spectroscopic tool perhaps even more powerful than in reactions with polarized deuterons.

Polarization effects in the elastic scattering of 3He and (3He, d) reaction on 58Ni

Abstract Angular distribution of analysing power of the elastic scattering of 3 He by 58 Ni and analysing power of the 58 Ni( 3 He, d) 59 Cu reaction leading to four excited states of 59 Cu were measured at 33.3 MeV using a polarized 3 He beam. The elastic scattering has been successfully described by phenomenological and “folding” optical-model calculations. The spin-orbit potential was found to be characterized by a small diffuseness parameter between 0.2 and 0.3 fm and strength around 4 MeV. The analysing power of the ( 3 He, d) reaction exhibits a strong j -dependence which is correctly predicted by the distorted wave theory using a 3 He potential determined from the elastic-scattering measurements.

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.

The elastic scattering of 3He particles of energy 24–29 MeV by C, N, A and I

Abstract The elastic angular distributions of 3 He particles scattered from carbon at 26.8 MeV, 25.3 MeV and 24.5 MeV, nitrogen at 25.7 MeV, argon at 26.4 MeV and iodine at 29.1 MeV, 28.2 MeV, 26.6 MeV, 24.6 MeV and 24.1 MeV have been measured using a nuclear plate camera. Results show a pronounced diffraction oscillation in light nuclei, becoming progressively weaker in argon, leaving an approximately exponential fall-off in cross-section in iodine. In iodine a ‘rise’ in cross-section above the Rutherford value immediately before fall-off has been observed. An optical model with a diffuse surface was used to analyse these data and the best fit parameters obtained.

Polarization in 3He elastic scattering and the 3He spin-orbit potential

Abstract Measurements by a double scattering technique are reported on the polarization produced in the elastic scattering at 25° lab, of 3 He particles of energies between 30.5 and 31.6 MeV from natural targets of beryllium, carbon, aluminium, titanium and copper. The observed polarizations are very small. Optical-model analysis of these results in conjunction with the angular distributions for elastic scattering of 3 He from these targets allows an upper limit to be set on the spin-orbit potential. It is found that a spin-orbit potential of less than 5 MeV is consistent with all the data, with a possible preferred range of 3–4 MeV.

The scattering of 29 MeV 3He-particles by 14N and 16O nuclei

The nuclear emulsion technique was employed to study the scattering of 29-Mev He/sup 3/ particles by N/sup 14/ and O/sup 16/ nuclei. Elastic angular distributions were analyzed in terms of a diffuse surface optical model; good agreement was found up to 50 deg (cms). The inelastic processes were compared with the predictions of the direct interaction mechanism. (auth)