M. Hugi

Large angle elastic scattering of 9Be ions on carbon isotopes

Abstract The differential cross sections for elastic scattering of 9 Be on the carbon isotopes 12 C and 13 C were measured at two different energies (11.4 and 14.9 MeV c.m.). The anomalously high cross sections for backward angles are explained as contributions of 3 He and 4 He exchange processes. The calculations were performed with an optical model for potential scattering and a finite range DWBA model for the transfer processes.

Elastic scattering of 9Be on heavy target nuclei

Abstract The elastic scattering of 9 Be ions on Mg, Al, Si, Ca, Ni, Ag and Au target nuclei has been studied at 14, 20 and 26 MeV projectile energy. Excitation curves on Si were measured at four angles in the energy range of 14–20 MeV. A universal optical potential fitting all these angular distributions was found and ambiguities of the parameters are discussed. For each target the interaction distance, the strong absorption distance and the sensitive regions were calculated.

Fusion and direct reactions for strongly and weakly bound projectiles

Abstract The interaction of 6 Li, 9 Be and 12 C projectiles with a 28 Si target was investigated by measuring the angular distributions of the elastically scattered projectiles and of the emitted protons, deuterons and α-particles. The experiment was performed in order to deduce direct and compound nucleus process contributions to the total reaction cross section and to study the influence of the projectile structure on the relative importance of these two mechanisms. Optical model parameters and therefore the total reaction cross section are strongly influenced by the binding energy of the projectile. The parameters of the Glas-Mosel model describing the fusion reaction vary smoothly with the atomic number. In the system 9 Be + 28 Si around 50% of all reactions are direct processes even at energies near the Coulomb barrier, whereas in the other systems the direct part amounts to 15 % ( 12 C) and 30 % ( 6 Li) only.

Energy dependence of fusion and reaction cross sections in the 9Be + 12C system

Abstract Angular distributions of protons, deuterons. tritons and α-particles were measured for the system 9 Be + 12 C at lab energies between 12 and 27 MeV. The compound nucleus model with level densities calculated according to the Gilbert-Cameron formula describes satisfactorily the measured proton, deuteron and triton data. In the α-particle spectra contributions from other processes seem to be present. In the analysis the fusion cut-off angular momentum was adjusted at each energy in order to reproduce correctly the proton, deuteron and triton channels. From this analysis the fusion cross section was determined as a function of the energy. The results were compared with fusion and total reaction cross section values calculated from a potential model with the real part of the interaction potential obtained from the double folding procedure of Satchler.

Light charged-particle production in the 9Be + 12C reaction at 11.4 MeV c.m. energy

Abstract Angular distributions of protons, deuterons, tritons and α-particles have been measured for the 9 Be + 12 C system at a c.m. energy of 11.4 MeV. The dominant process is compound nucleus formation. The fusion cut-off angular momentum and the fusion cross section were estimated from an analysis of the proton, deuteron and triton data. Contributions from other reaction mechanisms, e.g. cluster transfer, are responsible for α-particle emission. Spin selectivity in the excitation of a few states of the residua] nuclei was observed mainly in the proton channel.

Elastic scattering of 9Be on light target nuclei

Abstract The elastic scattering of 9 Be on the target nuclei 9 Be, 12 C, 13 C and 16 O was measured at projectile energies of 14, 20 and 26 MeV. All angular distributions show a diffraction-like structure. In addition, excitation curves were measured for the scattering of 9 Be on 9 Be at three different angles in the energy range of 9–22 MeV. An optical potential having parameters independent of mass number and energy and reproducing all the measured angular distributions in the forward angular region was found and compared with that for the scattering of 9 Be on medium and heavy nuclei.

The rôle of particle transfer in large-angle scattering of 1p-shell nuclei

Abstract The scattering of different 1p shell heavy ions on nuclei of the same species has been measured in the whole angular range up to 174°. Various pairs of interacting nuclei have been selected according to the different complexities of their properties which can influence the scattering through higher-order processes to different degrees. In general, the observed rise of the cross section in the backward region is satisfactorily described as a single-step transfer reaction. Second-order processes and compound-nucleus contributions are of no practical importance for the explanation of the elastic scattering data. The performed analysis, however, leaves some features in the experimental angular distributions not fully and satisfactorily understood.

A search for resonances in 9Be + 12C reactions in the energy range from 11.4 MeV to 14.8 MeV (CM)

Abstract Excitation curves for 9Be + 12C induced reactions with emission of protons, deuterons, tritons, α-particles and 8Be ions have been measured in the energy range from 11.4 MeV to 14.8 MeV (c.m.). Two strong maxima in the 8Be channel have been found at backward angles but no interchannel correlations were observed indicating the presence of a resonance. Three angular distributions of 8Be were measured in the vicinity of the 12.6 MeV maximum and analysed with a DWBA model.

The energy dependence of fusion in the 9Be+28Si system

Abstract The angular distributions of the energy spectra of the light charged particles (p, d and α) from the 9 Be + 28 Si reaction have been measured in the energy range 12 ≦ E lab ≦ 30 MeV. The particle evaporation spectra and the angular distributions were analyzed with a spin dependent statistical model. Angular distributions of 9 Be ions elastically scattered on 28 Si have been measured at the energies 12 MeV, 17 MeV, 23 MeV and 30 MeV and were analysed, together with previously measured cross sections, with the optical model. The fusion cut-off angular momentum l fus ( E ), the fusion cross section σ fus ( E ) and the ratio σ fus / σ R OM ( E ) were deduced. The excitation function for fusion was analyzed with the Glas and Mosel model. The parameters obtained from the fusion excitation function were compared with the corresponding ones from the 9 Be + 28 Si optical-model interaction potential.

Statistical significance of the deviation function in a search for resonances

Abstract To decide whether a structure observed in various excitation curves is merely a statistical fluctuation or due to a more interesting phenomenon (e.g. an intermediate resonance) the energy-dependent deviation function is used. The probability density of the deviation is derived from a statistical model and confidence limits are given.