R. Krücken

The YRAST Ball array

The Yale Rochester Array for SpecTroscopy, YRAST Ball, is described. Containing up to 30 Compton suppressed Ge detectors YRAST Ball is a powerful new array for c-ray spectroscopy. Several of its auxiliary detectors, including a multi-element solar cell array for heavy charged fragment detection and a new state of the art plunger system for recoil distance measurements are also described. ( 2000 Elsevier Science B.V. All rights reserved.

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.

Spin dependence of d5/2 neutron configurations in the wave functions of 92,94Zr from g-factor measurements

Abstract g factors of the 2 + 1 and 4 + 1 states in 92,94 Zr have been measured via Coulomb excitation of isotopically pure 92,94 Zr beams in inverse kinematics in combination with the transient field technique. The high precision results, g ( 92 Zr; 2 + 1 ) = −0.180(10) and g ( 94 Zr; 2 + 1 ) = −0.329(15) as well as the new data on the 4 + 1 state, g ( 92 Zr; 4 + 1 ) = −0.50(11), provide, for the first time, clear evidence of the dominant role of d 5/2 neutrons in the wave functions of these nuclei just above the N =50 shell closure. Moreover, the data imply increased purity of the d 5/2 neutron component in the wave function with increasing spin.

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).

SASSYER: An old instrument for new physics at Yale

Abstract The Wright Nuclear Structure Laboratory has recently acquired a gas-filled recoil separator previously used at Berkeley National Laboratory for heavy-element synthesis. The separator will be used to separate reaction recoils from primary beam particles and fission products following target bombardment. Commissioning of the separator has recently been completed, and the structure of 203 Rn investigated.

An Alternate Mechanism for E0 Transitions in Transitional and Deformed Nuclei

It is shown that the simple IBA‐1, which acts in a single space, robustly predicts a sharp rise in ρ2(E0; 02+ → 01+) values in spherical‐deformed transition regions, in agreement with the data. These predictions are effectively parameter‐free and provide an alternative to the usual coexistence model for these transitions.

The Highs And Lows Of The A=100 Region: Vibration-To-Rotation Evolution In Mo And Ru Isotopes

Nuclei below the Z = 50 magic shell gap with A∼100 show a wide variety of structural phenomena. These include excellent examples of vibrational collectivity at low-spins, which give way to more rotational-like excitations with increasing angular momentum. In this paper we present recent results from an experiment performed at Yale to study the yrast evolution of states in 98,99 Mo and 101,102 Ru. Although the high-spin data is consistent with predictions from rotational model theories, we propose a simple presciption to distinguish between vibrational and rotational regimes of angular momentum generation. When applied to the nuclei of interest, a clear picture emerges of how these two mechanisms of collective spin generation compete in this region.

SASSYER: A Gas‐filled spectrometer at Yale

The Wright Nuclear Structure Laboratory has recently acquired a gas‐filled recoil separator previously used at Berkeley National Laboratory for heavy‐element synthesis. The separator will be used to separate reaction recoils from primary beam particles and fission products following target bombardment. Commisioning of the separator has recently been completed, and the structure of 203Rn investigated.

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.

High‐spin states in neutron‐rich Rh isotopes

High‐spin states in the neutron‐rich 106,108,110,111,112Rh isotopes have been investigated in the fission of the compound system formed in three heavy‐ion induced reactions. Four bands were assigned to 106,108,110,112Rh, respectively. Comparison with the lighter odd‐odd Rh isotopes supports the assignment of the bands to the πg9/2 ⊗ vh11/2 configuration. In 111Rh the level scheme consists of two rotational bands. In the ground‐state band the odd‐proton occupies the πg9/2 orbital.