F. Auger

Proton elastic scattering on light neutron-rich nuclei

Abstract Proton-nucleus elastic scattering angular distributions have been measured for 6 He, 7 Li, 10 Be, 11 Be secondary beams. These data, together with other elastic scattering data for proton on unstable nuclei, have been analyzed using phenomenological and microscopic optical model approaches. To reproduce the experimental angular distributions for unstable nuclei, it was necessary to renormalize either the real or imaginary part of the optical potential. The influence of the break-up channels on the results is discussed.

16O elastic scattering at Elab = 94 MeV/nucleon

Abstract Elastic scattering of 94 MeV/nucleon 16 O on 40 Ca, 90 Zr, and 208 Pb was measured, completing similar measurements on 12 C and 28 Si. Optical model analysis of the whole set of data shows that the sensitive region where the nuclear potential is determined moves inwards as the mass of the target decreases. This determination is more precise for light systems which present a strong negative angle scattering contribution in the angular distribution. The data have also been analyzed in the framework of the folding model using density independent and density dependent nucleon-nucleon interaction. In both cases, the resulting potentials have to be renormalized to get a good description of the data. The data are consistent with a smooth decrease with energy of both the real and imaginary potentials.

Elastic scattering of 40Ar on 60Ni, 120Sn and 208Pb at 44 meV/u

Abstract Elastic scattering angular distributions of 44 MeV/u 40 Ar ions on 60 Ni, 120 Sn and 208 Pb targets have been measured in the forward angle region. Optical model analysis shows that near the grazing angle, the angular distributions are refractive and dominated by the Coulomb rainbow. The potentials have a smaller radius than empirical potential which fit low-energy data: this is consistent with a reduction of the real-ion potential at high energy.

Coupling effects in the elastic scattering of the exotic nucleus 6He on protons

Abstract Cross sections for the elastic scattering of 6He radioactive nuclear beam on proton targets have been measured at 38.3 MeV/nucleon. With a view to test the ability of general optical potentials to reproduce the data for scattering of unstable nuclei, the present results, as well as other existing data for 6,8He, have been analyzed within the framework of the microscopic Jeukenne–Lejeune–Mahaux nucleon–nucleus potential. The angular distributions were found to be best reproduced by reducing the real part of the optical potential. This renormalization can be seen as a consequence of the complex polarization potential produced by the coupling to the continuum due to the weakly bound nature of the unstable nuclei. This effect can be simulated in a phenomenological analysis by a surface potential.

24.5 A MeV 6He+p elastic and inelastic scattering

The structure of 6 He is explored with proton elastic and inelastic scattering to the first 2 + excited state (Q =− 1. 8M eV) of 6 He in the inverse kinematics using a 24.5 A MeV 6 He beam. The distorted wave approximation (DWA) with an optical potential obtained by folding an effective nucleon–nucleon (NN) g-matrix with the 6 He density matrix elements as given by a large basis shell model is used to analyse the data. The comparison of predictions with the data confirms the view that 6 He has

EXCITATION OF GIANT-RESONANCES IN PB-208, SN-120, ZR-90 AND NI-60 BY 84 MEV/NUCLEON O-17 IONS

Abstract Elastic and inelastic scattering of 1435 MeV 17O ions on 208Pb, 120Sn, 90Zr and 60Ni have been measured. Hindrance in the excitation of the first 3− states is observed. Parameters of the isoscalar giant monopole and quadrupole resonances are obtained. The quadrupole resonance exhausts ∼ 55% of the energy-weighted sum rule while the observed monopole resonance corresponds to more than 100% of the sum rule. Strength is also observed at high excitation energy in all targets.

Elastic scattering of 6He and its analysis within a four-body eikonal model

Abstract We have measured the elastic scattering of a 6 He secondary beam on a 12 C target at 41.6 MeV/u. The secondary beam was produced by fragmentation with SISSI, and transported to SPEG. The combined use of SISSI and SPEG allows very good quality data to be obtained in terms of energy and angular resolution. The cross section is analysed within a 4-body (α+n+n+ 12 C) eikonal scattering model which is completely parameter-free. Very good agreement with the data is found.

Search for the signature of a halo structure in the p(6He, 6Li)n reaction

Abstract The elastic scattering p( 6 He, 6 He)p and charge exchange reaction p( 6 He, 6 Li)n have been measured in reverse kinematics with a secondary 6 He beam. The angular distributions for these reactions were obtained. In the case of the charge exchange reaction, the ratio of the cross section for the Gamow-Teller transition to the ground state, and for the Fermi transition to the isobaric analog state is a measure of the relative strength of the two components of the exchange interaction, V στ and V τ . This ratio is found to be compatible with existing systematics for stable T = 1 nuclei, and no clear signature of a halo structure was found in the present data.

Heavy fragments emission in the 84Kr on 12C reaction at 35 MeV/nucleon☆

Abstract Heavy residues of collisions of 84 Kr + 12 C at 35 MeV/amu were measured using time of flight ΔE − E telescopes. An important part of the total cross section leads to events that have all the characteristics of an equilibrated composite system decaying by heavy fragment emission. The experimental yields are well reproduced using a statistical model.

The Giant Dipole Resonance in hot Sn nuclei

Abstract We have studied the Giant Dipole Resonance (GDR) built on the excited states of 112Sn formed in the fusion of 19F with 93Nb. The excitation energy of the compound nucleus 112Sn was 130 and 152 MeV. High-energy γ-rays were detected in a 7-element BaF2 cluster and 4 NaI(Tl) scintillators. Coincidences with the evaporation residues detected in two parallel-plate avalanchecounters ensured that the γ-rays were associated with fusion events. In order to study the characteristics of the GDR, we have performed analyses of the γ-ray spectra within the statistical model, using a continuous evolution of the GDR centroid energy with the mass and the temperature of the emitting nucleus, and a nuclear temperature dependent level density parameter. The theoretical prescriptions concerning the evolution of the GDR width with excitation energy have been tested. We show that, in order to reproduce the γ-spectra, the increase of the width must be more rapid than the two theoretical predictions. The width has to reach large values, of the order of 15 to 20 MeV above 100 MeV of excitation energy. These values are greater than the saturation value of about 12 MeV which has been published following the analyses using constant parameters. On this condition, the shape of the spectra can be reproduced with or without a saturation of the width. It is therefore not possible to say if the increase of the width is due to angular momentum effects or to collisional effects.