W. A. Seale

SACI—a 4π plastic phoswich array ancillary detector system of a γ-ray spectrometer

A large solid angle low-Z charged particle detector system was built in order to improve the quality of the identification and selection of evaporation channels for in-beam g-spectroscopy measurements. The array consists of 11 plastic phoswich telescopes closely packed in a 4p arrangement and to be used as an ancillary system for the Pelletron Laboratory g-ray spectrometer. The new system was tested in g-particle and g–g-particle coincidence measurements using the 27 Al þ 16 O and 100 Mo þ 11 B reactions, at 53 and 43 MeV incident beam energies, respectively. The values for the particle detection efficiency and improvement in the peak to background ratios are considered acceptable for the usefulness of the system. r 2002 Elsevier Science B.V. All rights reserved.

Nuclear structure in odd-odd nucleus 138 Pr

With the view of extending the systematics of odd-odd Pr nuclei toward the N=82 closed shell, high-spin states in 138Pr nucleus have been investigated with the 128Te(14N, 4nγ) reaction. Configurations and spin assignments are suggested for three of the observed band-structures.

Measurement of fusion cross sections for 16O+16O

In earlier works, the fusion cross section for the 16O+16O reaction has been measured using different techniques. In the present work, we have obtained an experimental excitation function for 16O+16O using γ-ray spectroscopy. The measurements were performed at center-of-mass energies between 8.28 and 12.25 MeV. The theoretical predictions obtained with a coupled-channel model are consistent with the experimental data. From our analyses, the extrapolated S-factor value at 6.6 MeV, corresponding to the Gamow peak energy for core oxygen burning conditions, is about 3.6 × 1025 MeV barn.

First allowed bandcrossing in neutron deficient nucleus 141Tb

The neutron deficient 141Tb nucleus has been studied with the 92Mo (54Fe, ap) reaction at 240-MeV incident energy and the multidetector array GASP. For the yrast ph11/2 decoupled band, excited states up to 6.7 MeV and spin up to 47/2- have been observed. This band presents an upbend at rotational frequency of w = 0.38 MeV due to the alignment of h11/2 protons. The results are discussed in terms of the Cranking model.

Stopping power of Au for silver ions at low velocities

Energy loss measurements for the slowing down of Ag ions in Au, in the velocity range 1:6v0 < v < 4:4v0, where v0 is the Bohr velocity, are presented. The measurements were performed using the Doppler shift technique and also with a new method, where a secondary beam of low velocity heavy ions is produced by elastic scattering of the accelerated beam. The results are compared to the SRIM2000 calculations (www.srim.org) and to recent measurements in this velocity region.

Installation of the IMPAC technique in the Pelletron laboratory

A special target chamber for the direct production & recoil implantation of radioactive probes for perturbed angular correlation has been constructed and tested. Feasibility studies were made by reproducing the known quadrupole frequencies at 77Br and 111In probes in metallic zinc. Preliminary results were obtained on the lattice site dependence of Cd hyperfine field in Pd2MnSn Heusler alloy with the PAC technique.

Elastic and inelastic angular distributions of the 7Li+120Sn system for energies near the Coulomb barrier

The reaction of 7Li+120Sn has been measured at bombarding energies of 21, 24 and 27 MeV. The -ray transition in 120Sn was observed and the angular distribution for the 2+ excited state was obtained. Coupled channels and coupled-reaction channels calculations, including the dynamical polarization potential due to the projectile break-up, obtained from continuum discretized coupled channel calculations, were performed. The comparison between the existing experimental elastic angular distribution with the coupled-reaction channels calculations indicates that the 1n stripping transfer is the most intense channel to be coupled and the 2n stripping reaction occurs sequentially rather than directly, however, further data must be analyzed to confirm this indication. The experimental elastic and inelastic scattering data were well described by the calculations, but some discrepancies in these channels may indicate the need for corrections to the nuclear potential and/or the necessity to incorporate further channels.

In-beam gamma ray spectroscopy of 58Co

The odd-odd 58Co nucleus has been studied with the 51V(10B, p2n) reaction at 33-MeV incident energy and the g-spectrometer Saci-Perere. Excited states up to 8.0 MeV and spin up to 11+ have been observed. The results are compared to Shell Model calculations using the GXPF1 effective interaction, developed for use in the fp shell. The pf7/2-1An(p3/22f5/21) configuration was assigned to the yrast levels.

Nuclear reaction studies with particle-gamma coincidences using the Saci-Perere spectrometer

The Saci-Perere spectrometer of the University of Sao Paulo has been configured to perform particle-gamma coincidence measurements in order to study nuclear reaction mechanisms. The motivation of this type of measurement comes from the recent development of nuclear reaction models based on the Sao Paulo potential with the inclusion of an imaginary part with no adjustable parameters. New preliminary data on the 18O+110Pd transitional system are presented, and apparent similarities to weakly bound cases (e.g. 7Li + 120Sn) are briefly discussed.

Stopping Power of Au for Ti Using Elastic Recoil Technique

The slowing down of heavy ions in matter is still not well understood especially at low energies (<0.5 MeV/u). In this contribution we present new experimental data for the stopping power of Au for Ti ions using an elastic recoil technique where a heavy-ion beam at low energies is produced by elastic scattering of an energetic primary beam imping on a thin target. Atoms from the target recoil at low energies. We compare our experimental data with previous data and with semi-empirical and theoretical models.