R. K. Bock

OPTICAL-MODEL ANALYSIS OF THE ELASTIC SCATTERING OF COMPLEX NUCLEI AT LOW ENERGIES.

Abstract Angular distributions of the elastic scattering of 10 B, 11 B, 16 O and 19 F on 12 C and 16 O on 11 B were measured at incident energies between 18 and 60 MeV. The data were analysed with the optical model. When applying the concept of strong absorption at small internuclear distances, a consistent description for the various cases was found. In the analysis, special attention was paid to the interference effects of the elastic scattering with the exchange transfer.

(3He, α) reactions on the chromium isotopes

Abstract The reactions 50,52,53,54Cr(3He, α)49,51,52,53Cr have been studied at an incident energy of 18 MeV using a broad-range magnetic spectrograph as well as solid state detectors. Angular distributions were obtained for all isotopes. The relative isotopic cross sections were accurately determined by measurements with a target of mixed Cr isotopes. Coulomb energy displacements are obtained from the observation of f 7 2 , d 3 2 and s 1 2 analogue states at excitation energies between 5 and 13 MeV. The spectroscopic factors from a DWBA analysis give information about the neutron configurations in the Cr isotopes which are discussed in the particle-hole excitation picture and in terms of the unified model. Centres of gravity for the f 7 2 , d 3 2 , and s 1 2 orbits are determined. The spectroscopic factors of the analogue states are obtained from solutions of the Lane equations for the bound states using a surface-type isospin potential. In a simplified analysis, the effects of the surface potential are simulated by varying the bound-state radii, keeping the depth of the potential constant for the ifT states. These procedures yield similar results, which are in agreement with the sum-rule predictions. The resulting radii suggest that the inner nucleons occupy a volume smaller than that corresponding to a potential radius R = 1.25 A 1 3 .

Investigation of the reaction 12C(7Li, t)16O

Abstract Angular distributions of the reaction 12 C( 7 Li, t) 16 O have been measured at E lab = 15, 21.1 and 24 MeV with a magnetic spectrograph and a d E /d x — E telescope. From the shape of the angular distributions and the weak excitation of the 2 − state at E x = 8.87 MeV in 16 O it is concluded that the reaction proceeds dominantly by a direct α-transfer. Contributions from compound nucleus formation were estimated from a Hauser-Feshbach calculation. The angular distributions were analysed by means of the DWBA, which has been modified to take into account the relative p-state between the α-particle and the triton in 7 Li. Approximations valid for a surface reaction were used to simplify the theory. The calculations are able to reproduce the essential features of the angular distributions. Reduced α-widths were extracted for some states in 16 O.

TRANSFER REACTIONS BY HEAVY IONS AND FINITE-RANGE DWBA CALCULATIONS.

Abstract Experimental data of one-, three- and four-nucleon transfer reactions induced by the heavy-ion projectiles 16 O and 19 F on the targets 11 B and 12 C are analyzed within the framework of finite-range DWBA. In many-nucleon transfer reactions, the cross section is composed of the coherent sum of amplitudes corresponding to the transfer of clusters with different intrinsic states. The spectroscopic amplitudes are calculated using the results of the intermediate-coupling shell model. The calculated cross sections can reproduce the experiments fairly well in most cases. The method is compared with other approximations from the viewpoint of the selection rules for the angular-momentum transfer.

(d, 6Li) reactions on p and sd shell nuclei and their interpretation by finite-range DWBA

Abstract The (d, 6 Li) reaction on 10 B, 11 B, 12 C, 16 O, 19 F, 28 Si and 40 Ca has been investigated with the 19.5 MeV deuteron beam of the MPI Emperor tandem Van de Graaff. The measured angular distributions are analyzed by finite-range DWBA calculations. Spectroscopic factors for the α-cluster transfer have been calculated from shell-model wave functions for the target nuclei. The theoretical cross sections are found to be very sensitive to the choice of the model for 6 Li. The cluster model leads to cross sections which are strongly enhanced compared to the shell-model predictions. They reproduce the absolute experimental cross sections of the ground state transitions for the target nuclei from 12 C to 40 Ca. However, the experimental (d, 6 Li) cross section on the 10 B target is much larger than predicted and the angular distribution cannot be described. This indicates a more complicated reaction mechanism in this case.

Nuclear spectroscopy with heavy-ion induced proton-transfer reactions in light nuclei

Abstract Angular distributions of the proton-transfer reactions 11 B( 16 O, 15 N) 12 C at E lab = 27, 30, 32.5, 35 and 60 MeV and 12 C( 19 F, 20 Ne) 11 B at E lab = 40, 60 and 68.8 MeV to ground and excited states of both final nuclei were measured. A DWBA analysis based on the method of Buttle and Goldfarb shows, that a consistent description of all data is possible with those optical-model parameters, which are obtained from the analysis of the elastic scattering data by applying the concept of strong absorption. The relative spectroscopic factors are independent of energy and in good agreement with theoretical values and those obtained by conventional reactions. The absolute values agree within a factor 1.5 in the 16 O on 11 B case.

Four-nucleon transfer reaction induced by 10B on 12C

Abstract The four-nucleon transfer reaction induced by 10 B on 12 C has been studied above the Coulomb barrier. The population of final states of 16 O is less selective than in other four-nucleon transfer reactions induced by 6 Li, 7 Li, or 16 O. This fact as well as the structureless angular distributions can be explained by the complexity of the structure of the ground state of 10 B, which has large components with a lower degree of symmetry than the α-particle.

LEVEL STRUCTURE OF

Abstract The level scheme of 49V has been investigated using the 50 Cr ( t , α) and 48 Ti ( 3 He , d ) reactions. Angular distributions have been measured and spectroscopic factors have been extracted by DWBA analysis. The data indicate particle-hole and configuration mixing in the proton states involved. The excitation of states of the ( f 7 2 ) 3 configuration is discussed in connection with possible target excitation processes.

sup 49

Abstract Alpha-particle transfer leading to 16 O states was investigated by lithium-induced reactions. It is shown that the compound nucleus contribution is very small in ( 7 Li,t) in contrast to ( 6 Li,d). The strong population of the 6.92 MeV 2 + and the 10.35 MeV 4 + state in 16 O gives evidence for the 4p-4h structure of these levels.

V DEDUCED FROM

Abstract The elastic scattering of 16 O on 17 O has been measured at E lab = 24, 28 and 32 MeV and θ c.m. = 90° −150°. At large energy the cross section exhibits a structureless rise at backward angles which can be described consistently with the DWBA approach for the elastic transfer.