D. Torresi

Measurements of α-decay half-lives at GSI

One of the major problems in nuclear astrophysics concerns the estimation of electron screening effects on nuclear reaction rates. We have proposed investigating the electron screening effects of nuclear systems which decay via α-particles, using fragmented beams at relativistic energies produced at the present GSI FRS-ESR facility. By looking at the modification of the half-lives and Qα-value of highly charged emitters, we expect to estimate the electron screening energies.

Scattering process for the system 7Be + 58Ni at 23.2 MeV beam energy

We measured for the first time the scattering process of 7Be nuclei from a 58Ni target at 23.2 MeV beam energy. The experiment was performed at the Laboratori Nazionali di Legnaro (LNL, Italy), where the 7Be Radioactive Ion Beam was in-flight produced with the facility EXOTIC. Charged reaction products were detected by means of the detector array DINEX, arranged in a cylindrical configuration around the target to ensure a polar angle coverage in the ranges θcm = 40°-80° and 110°-150°. The scattering differential cross section was analyzed within the optical model formalism with the coupled-channel code FRESCO to extract the total reaction cross section. The result was compared with those obtained at lower beam energies in an earlier experiment performed at the University of Notre Dame (USA). At the present stage of our analysis, the two data sets were found to be not fully consistent each other.

Reaction Dynamics for the Systems 7Be, 8B + 208Pb at Coulomb Barrier Energies

In this contribution we describe the first results obtained for the investigation of the elastic scattering process in the reactions induced by the Radioactive Ion Beams Be and B on a Pb target at Coulomb barrier energies. The experimental data were analyzed within the framework of the optical model in order to extract the total reaction cross section. The comparison with data available in literature for reactions induced on Pb by light ions in the mass range A = 6-8 shows that the loosely-bound B has the largest reactivity.

Elastic scattering and transfer reactions for the system 7Be + 58Ni at Coulomb barrier energies

We investigated the reaction induced by the Radioactive Ion Beam 7Be on the closed proton shell nucleus 58Ni at 22.0 MeV bombarding energy. The 7Be beam was produced by means of the in-flight technique with the facility EXOTIC at INFN-LNL (Italy). Charged reaction products were mass and charge identified in a rather wide angular range and their energy distributions were analyzed to infer some information on the production mechanism. The relevance of direct processes, especially 3He- and 4He-stripping, as well as compound nucleus reactions is critically reviewed.

Dynamical Dipole mode in heavy-ion fusion reactions in the 192Pb mass region

The dynamical dipole mode was investigated in the mass region of the 192Pb compound nucleus, by using the 40Ca + 152Sm and 48Ca + 144Sm reactions at Elab=11 and 10.1 MeV/nucleon, respectively. Both fusion-evaporation and fission events were studied simultaneously for the first time. Our results for evaporation and fission events (preliminary) show that the dynamical dipole mode survives in reactions involving heavier nuclei than those studied previously.

β-delayed α decay of 16N and the 12C(α,γ)16O cross section at astrophysical energies: A new experimental approach

The 12C(α,γ)16O reaction at energies corresponding to the quiescent helium burning in massive stars is regarded as one of the most important processes in nuclear astrophysics. Although this process has being studied for over four decades, our knowledge of its cross section at the energies of interest for astrophysics is still widely unsatisfactory. Indeed, no experimental data are available around 300 keV and in the energy region of astrophysical interest extrapolations are performed using some theoretical approaches, usually R-matrix calculations. Consequently, the published astrophysical factors range from 1 to 288 keVb for SE1(300) and 7 to 120 keVb for SE2(300), especially because of the unknown contribution coming from subthreshold resonances. To improve the reliability of these extrapolations, data from complementary experiments, such as elastic and quasi- elastic α scattering on 12C, α-transfer reactions to 16O, and 16N decay are usually included in the analysis. Here the β-delayed α decay of 16N i...

13C+4He resonant elastic scattering on a thick gas target

Resonant elastic scattering of 13C on a thick 4He target has been measured. Reaction products from 13C(4He, 4He) were detected at several beam energies and gas pressures. Raw yield was efficiency corrected using Monte Carlo simulations and an averaged yield spectrum was produced. The observed peaks correspond well to the previously measured elastic scattering data.