W. von Oertzen

On the interaction induced by the exchange of nucleons between two identical nuclear cores

Abstract A formula for the interaction energy of a nuclear system comprised of two nuclei A and B, with B having a large probability to be represented as B = (A+c), is derived. A general formula for the interaction via the exchange of a particle c between two identical cores has been obtained. The scattering of a nucleus B on a nucleus A under the influence of the exchange interaction is discussed. Calculations for the scattering of 12 C on 13 C and 16 O on 12 C have been performed and very good agreement with experimental data has been obtained.

Theory of particle and hole transfer in elastic nucleus-nucleus scattering

Abstract The optical model description of elastic nucleus-nucleus scattering is generalized to include the transfer of particles and holes in collisions between heavy nuclei which differ only by one or a few nucleons. An elementary model which consists of two identical cores and a valence particle is solved for small valence-particle masses in the molecular two-state approximation. The molecular states of the valence particle are constructed by a linear combination of nuclear orbitals (LCNO). In order to get around the problem of Coriolis coupling the scattering solution is restricted to cases where nuclear states with j ≦ 1 2 or l = 0 are involved. Because of the possible exchange of the valence particle between the two identical cores, even and odd partial waves are scattered by different potentials. The difference is due to exchange potentials which are associated with the molecular states of definite core-permutation symmetry. The result is a characteristic interference pattern in the angular distribution of the elastic cross section. The elementary model is generalized by describing the cores in the framework of Hartree-Fock theory. This description shows that holes can be exchanged like particles. The derivation of an optical core-core potential is given. The exchange potential which is real in the elementary model becomes complex in the general treatment. For the elastic transfer of two particles, two holes or a particle and a hole, four possible approximations are discussed. Correlations between core particles and valence particles or holes can approximately be taken into account by spectroscopic factors in the exchange potentials.

Molecular scattering states of the neutron in the elastic scattering of 12C on 13C

Abstract The angular distributions of elastic scattering of 12 C on 13 C at 15 MeV and 19 MeV (Lab) have been remeasured in the full angular range using a magnetic spectrometer. The analysis of the data based on the method of molecular wave functions is discussed using the two center shell model (TCSM) and linear combination of nuclear orbitals (LCNO) approaches for the scattering states of the neutron.

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.

Nucleon exchange in the low-energy scattering of α-particles on 6Li and 7Li

Abstract Excitation functions for the elastic scattering of α-particles on 6 Li and 7 Li were measured between 2.5 and 4.5 MeV. Angular distributions have been measured at 3.0 and 4.0 MeV for 6 Li and 3.6 MeV for 7 Li, at energies well separated from compound nucleus resonances. The increase of the differential cross section above the Rutherford scattering could be well described by the exchange of a deuteron for 6 Li using the methods of molecular wave functions. The extracted spectroscopic amplitude for the deuteron is 1.0, which agrees well with the values of the cluster model. For 7 Li no analysis was performed. This case is more complicated, the transfer of the triton in a 3 2 − configuration involving an l = 2 transfer and due to the presence of a strong inelastic transition to the 1 2 − state in 7 Li.

Heavy ion transfer reactions with identical initial and final states

Abstract A special type of transfer reaction which has identical initial and final states and which is strongly localized in angular momentum space is discussed. These reactions A(B, A)B are due to exchange effects in elastic scattering A(B, B)A. Examples for α-particle and proton transfer have been measured and analysed.

Elastic and inelastic scattering of16O by12C at forward and backward angles

Angular distributions of the reactions12C(16O,16O)12C and12C(16O,12C)16O have been measured in the angular range of θCM=10 °–60 ° at 65 and 80 MeV to ground states and excited states of both final nuclei. An optical model withl-dependent imaginary potential gives no consistent description of the elastic scattering data. It is shown, however, that the forward angle elastic scattering may be described by strongly absorbing potentials and that the backward rise of the cross sections in both the elastic and inelastic transitions can be explained by a four nucleon transfer12C(16O,12C)16O.

Diffraction model interpretation of heavy ion induced transfer reactions

Abstract Angular distributions for p- and α-particle transfer in the reaction 11 B( 16 O, 15 N) 12 C have been measured for transitions to the ground state and the 6.33 MeV level of 15 N at E( 16 O ) = 27, 30, 32.5 and 35 MeV. The ground-state angular distribution shows strong and regular oscillations which can be well described by the diffraction model. The appearance of the diffraction structure giving information on (about) the transferred angular momentum can be explained by angular momentum matching considerations.

Nucleon exchange in scattering of carbon isotopes

Abstract The elastic scattering of 12 C on 13 C and 14 C, of 13 C on 14 C has been measured in the vicinity of the Coulomb barrier. The structure of the angular distributions is consistently described using the method of molecular wave functions which takes into account the exchange of the valence particles.