B. Fernandez

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.

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.

16O + 28Si elastic scattering at EL=94 MeV/nucleon

Abstract 16 O + 28 Si elastic scattering has been measured at E Lab =94 MeV/nucleon. The angular distribution is sensitive to the real part of the ion-ion potential over a broad domain extending from 5 to 8 fm. i.e. well inside the strong absorption radius (7.3 fm) and overlapping the sum of the nuclear radii (5.7 fm). The data are not well described by a standard double-folded potential based on the M3Y interaction. A good fit is obtained when using a density-dependent generalization of this interaction.

CHARGE-EXCHANGE REACTION INDUCED BY 6HE AND NUCLEAR DENSITIES

Abstract The charge-exchange reaction p( 6 He, 6 Li)n is studied in reverse kinematics with a secondary 6 He beam at 41.6 MeV/nucleon. The transition connecting the ground state of 6 He to its isobaric analog state in 6 Li has been measured and analyzed in the context of a microscopic calculation. The angular distribution is shown to be sensitive to the nuclear interaction potential and to the radii of the density distribution of 6 He. It is shown that only a coherent microscopic analysis may disentangle the different contributions.

Elastic scattering and charge exchange reaction with light neutron rich exotic beams

Abstract The elastic scattering of 6 He, 10,11 Be secondary beams on a (CH 2 ) 3 target and the charge exchange reaction p( 6 He, 6 Li)n have been measured. A microscopic optical potential was used to reproduce the proton-nucleus elastic scattering data. No clear signature of a halo structure was found in the present data for the elastic scattering and charge exchange reaction, due to the lack of large angle measurement.

Compound nuclear lifetimes at high excitation energies via a new statistical fluctuation method

Abstract A new method to determine compound nuclear lifetimes at high excitation energies is proposed and applied to the system 12 C( 28 Si, α ) 36 Ar at two different bombarding energies, 190 and 277 MeV. The alpha particle spectra show a structure which directly reflects the fluctuating behavior of the first de-excitation step. Coherence widths and thus lifetimes for the nucleus 36 Ar were obtained via a correlation function analysis. The results at low excitation energies are consistent with standard statistical models while the result at high excitation energy is compatible with a theoretically predicted change of the level density parameter.

Charge-exchange reaction with light neutron-rich beams

The charge exchange reaction p(, )n was studied in reverse kinematics with a secondary beam at 41.6 MeV/nucleon. The transitions connecting the ground states and the one leading from the ground state of to its isobaric analogue state in have been measured and analysed. Their ratio is a measure of the relative strength of the two components of the exchange interaction, and . No clear signature of a halo structure is found from this ratio, since it is found to be compatible with existing systematics for stable T = 1 nuclei. The sensitivity of the (p,n) charge exchange angular distributions to the nuclear interaction potential and to the rms radii of the density distribution of is studied.