J. R. Cooper

Low-spin structure of 156Dy through gamma-ray spectroscopy

Excited states of 156Dy were populated by beta decay and studied through gamma-ray spectroscopy. Extensive data led to improved information of the electromagnetic properties of low-spin states and to a substantially revised level scheme. The results are compared to those of other N=90 isotones and to predictions of the X(5) dynamical symmetry.

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.

Nature of excited 0+ states in 154Sm

Abstract Lifetimes of the 0 2 + and 2 γ + states in 154 Sm were measured using the Doppler-shift Attenuation Method following Coulomb excitation. The experiment employed the gamma-ray detector array YRAST Ball at Yale University in conjunction with an array of photo-electric cells. 154 Sm was identified as one of the few deformed nuclei where the first excited 0 + state is the β -vibration of the ground state. The 0 3 + level has no collective decay to the ground state band and is interpreted as a spherical shape coexisting state based on its decay properties and calculations in the framework of the interacting boson model (IBM) and geometric collective model (GCM).

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.

Mass measurements of {sup 70}Se, {sup 71}Se, {sup 72}Br, and {sup 73}Br

The path and termination point for the rapid proton-capture (rp) process above {sup 56}Ni is uncertain due to a lack of knowledge of nuclear properties, especially masses, near the proton drip line. To address this need we have begun a program to measure masses along the rp-process path in the A{approx}60--80 region using {beta}-{gamma} coincidence spectroscopy. Q{sub EC} values derived from {beta}{sup +} spectrum end points were used to calculate mass excess values for {sup 70}Se, {sup 71}Se, {sup 72}Br, and {sup 73}Br. The results are compared to predictions of mass models and to estimates based on systematic trends in this region.

Mass measurements along the rp-process path

The path and termination point for the t-p-process above {sup 56}Ni is uncertain due to a lack of knowledge of nuclear properties, especially masses, near the proton drip line. To address this need we have begun a program to measure masses of nuclei along the r-p-process pathway in the A{approximately}60-80 region using {beta}-{gamma} coincidence spectroscopy. Results for {sup 71}Se are presented and a preliminary experiment for {sup 72}Br is described.