T. A. Lewis

B(E2) values from low-energy Coulomb excitation at an ISOL facility: the N=80,82 Te isotopes

B(E2;0+1→2+1) values for the unstable, neutron-rich nuclei 132,134Te were determined through Coulomb excitation, in inverse kinematics, of accelerated beams of these nuclei. The systematics of measured B(E2) values from the ground state to the first excited state have been extended to the N=82 shell closure in the Te nuclei and have been compared with the predictions of different theories. The measurements were performed at the Holifield Radioactive Ion Beam Facility (HRIBF) using the GRAFIK detector. The success of this approach, which couples a 5.7% efficient through-well NaI(Tl) γ-ray detector with thin foil microchannel plate beam detectors, also demonstrates the feasibility for Coulomb excitation studies of neutron-rich nuclei even further from the valley of beta stability, both at present-generation ISOL facilities and at the proposed Rare Isotope Accelerator.

Tagging of isobars using energy loss and time-of-flight measurements

Abstract The technique for tagging isobars in a mixed beam using differences in energy lost in an absorber by different isobars has been tested. As expected, isobar separation does improve by allowing more energy loss (thicker absorbers), but such gains could be realized only after achieving good absorber homogeneity. For heavy ions accelerated to low and moderate energies ( MeV / A ) , we found that when homogenous absorbers are used, the largest impediment to achieving good isobar separation rests with uncertainties in energy caused by straggling in the absorber. Measurements of beam energy loss and energy spread were shown to come close to predicted values when accounting for both collisional and charge-exchange contributions to the calculated energy straggling. Reliable prediction of energy straggling then allowed us to study the efficacy of this method for isobar separation when applied to different mass ranges and beam energies. Time-of-flight was used to measure energy loss since this method allows handling of counting rates in excess of 1 MHz and the demands on timing detector resolution and length of flight path were moderate for all cases under study here. Partial separation in a most difficult case, an analyzed beam of A=132 isobars at energies near 3 MeV / A has been demonstrated. The time-of-flight information can be added to the data stream for events of interest, as an additional parameter (tag) to the online data stream. Such event-by-event tagging enables one to study the effect of difference in isobaric mixture in the beam on the reaction outcome even when isobar separation is not complete.

Experiments with Radioactive Nuclear Beams for Nuclear Structure

Radioactive Nuclear Beams (RNBs) are opening new regions of the nuclear landscape to nuclear structure studies. Early experiments with RNBs rely on reactions with large cross sections, inverse kinematics, and very efficient detector geometries in order to measure observables that are very sensitive to structural features. A Coulomb excitation experiment extracted the B(E2;01+ → 21+) values of the neutron rich RNBs 132,134Te at the HRIBF with the GRAFIK through‐well NaI(Tl) detector. In addition, other experiments with RNBs, such as Coulomb excitation of octupole states and reorientation experiments, inelastic scattering, and single‐particle transfer, will be discussed.