No abstract

The 7 Li+ 28 Si elastic scattering was studied at near-barrier energies, namely, 8, 8.5, 9, 10, 11, 13, 15, and 16 MeV, with the aim to map the real and imaginary part of the optical potential and therefore probe the threshold anomaly. Angular distributions were measured over a wide angular range of ( lab = 25°to 150°) for the lower energies and of ( lab = 10°to 100°) for the higher energies. The present data, together with previous ones on heavier targets ( 138 Ba and 208 Pb) at near barrier energies, were analyzed by using optical potentials obtained in a double-folding framework. The results were compared with previous measurements of 6 Li on the same targets. It was found that a striking difference occurs between the imaginary potentials of 6 Li and 7 Li, which, respectively, present an increasing and decreasing behavior approaching the barrier from higher to lower energies. On the other hand, this energy variation is not fully reflected to the real part of the potential, as it is described by dispersion relations. The strength of the real potential remains almost constant with a weak declining and uprising trend for the 6 Li and 7 Li, respectively. For a better understanding of our results, continuum-discretized-coupled-channel calculations were also performed and are discussed.

We have measured the neutron capture cross sections of the stable magnesium isotopes 24,25,26 Mg in the energy range of interest to the s process using the neutron time-of-flight facility n_TOF at CERN. Capture events from a natural metal sample and from samples enriched in 25 Mg and 26 Mg were recorded using the total energy method based on C 6 2 H 6 detectors. Neutron resonance parameters were extracted by a simultaneous resonance shape analysis of the present capture data and existing transmission data on a natural isotopic sample. Maxwellian-averaged capture cross sections for the three isotopes were calculated up to thermal energies of 100 keV and their impact on s-process analyses was investigated. At 30 keV the new values of the stellar cross section for 24 Mg, 25 Mg, and 26 Mg are 3.8±0.2 mb, 4.1±0.6 mb, and 0.14±0.01 mb, respectively.

The 62Ni(n,gamma)63Ni(t(1/2)=100+/-2 yr) reaction plays an important role in the control of the flow path of the slow neutron-capture (s) nucleosynthesis process. We have measured for the first time the total cross section of this reaction for a quasi-Maxwellian (kT=25 keV) neutron flux. The measurement was performed by fast-neutron activation, combined with accelerator mass spectrometry to detect directly the 63Ni product nuclei. The experimental value of 28.4+/-2.8 mb, fairly consistent with a recent calculation, affects the calculated net yield of 62Ni itself and the whole distribution of nuclei with 62

The neutron Time of Flight (n_TOF) facility at CERN is a source of a wide-range (1 eV