K. Theine

High-spin states in 163–166Hf

Abstract High-spin states in 163–166 Hf, populated in 148,150 Sm ( 20,22 Ne , x n ) reactions, have been studied by in-beam γ-ray spectroscopy using the first four to six Compton-suppressed Ge detectors from the OSIRIS set-up. Levels up to I > 30 kh are identified. The results are interpreted within the framework of the cranked shell model. Good agreement is obtained between experiment and calculation for the two and three quasi-neutron alignments in all four isotopes. The nature of the second band crossing in the even- A isotopes is discussed.

First observation of high-spin states in 167Ta and 168Ta

Abstract Excited states in 167 Ta and 168 Ta, populated in the 142 Nd( 30 Si, p x n) reaction, were investigated using the ESSA30 array with 29 Compton-suppressed Ge detectors. Several rotational decay sequences are identified and for the first time a high-spin level scheme is established for these nuclei. The results for 167 Ta are discussed in comparison with existing data in the neighbouring nuclei and with cranked shell model calculations. The possible intrinsic structure and its consequences for the yrast band in 168 Ta are also briefly discussed.

Spectroscopy of195Hg and196Hg

High-spin states in the oblate-deformed nuclei195Hg and196Hg were populated in the198Pt(α, xn) reaction and investigated by in-beamγ-ray spectroscopy using six Compton-suppressed Ge detectors. The level schemes of both nuclei are extended considerably. The level structure is interpreted within the framework of the cranked shell model. Good agreement is obtained between model predictions and experimental results.

Lifetime measurements of high spin states in Yb nuclei

Abstract Transition rates for high spin discrete line states in 168 Yb have been extracted using a Doppler Shift Attenuation Method and a loss of collectivity has been found at the highest spins. Similar results for other Yb nuclei are reviewed and an explanation, involving a reduction of deformation due to changes of intrinsic structure, is given. It is shown that this loss of collectivity for the yrast and near-yrast bands is in sharp contrast to the recent finding that the transitions contributing to the ridge structure in a γ-γ coincidence matrix retain full collectivity up to the highest spins. Possible reasons for this difference are discussed

Superdeformation in 194Pb

Abstract A superdeformed band has been identified in 194 Pb, populated in the 158 Gd( 40 Ar, 4n) reaction. The dynamic moment of inertia J (2) is very similar to the ones of the superdeformed bands in 192 Hg and 194 Hg. This suggests that the high- N intruder configuration π 6 4 ν 7 4 determines the properties of the superdeformed core also in 194 Pb.

High-spin structure of 167W and 168W

Abstract Excited states in 167 W and 168 W, populated in the 142 Nd ( 30 Si , x n ) reaction, were investigated at high spins using the ESSA30 array with 29 Compton-suppressed Ge detectors. The level schemes are extended to higher spins and several new rotational bands are identified. The results are discussed in comparison with existing data on the neighbouring N = 93 and 94 isotones and on the Z = 74W isotopes. A theoretical analysis is presented within the framework of a pairing-self-consistent cranked shell model using shape parameters obtained from total-routhian-surface calculations.

Spectroscopy of 160Hf

Excited states in 160Hf were investigated up to spins I≈20h using the OSIRIS array of 12 Compton-suppressed Ge detectors and a calorimeter of 48 BGO detectors. The results are interpreted within the framework of the cranked shell model. The systematics of the band crossing frequencies in the Hf isotopes are discussed. An analysis of the high-spin states in terms of double routhians shows the reduction of pair correlations with increasing rotational frequencies. NUCLEAR REACTIONS 144Sm(20Ne, xn), E= 105−120 MeV; 144Sm(19F,xn), E=

Dipole cascades in194Pb

Excited states in194Pb, populated in the158Gd(40Ar,4n) reaction, were investigated using the OSIRIS γ-ray spectrometer array. The previously known level scheme is revised and substantially extended. Four cascades of dipole transitions are discussed.

High-spin states in205Bi

High-spin states in205Bi, populated in the205Tl(α, 4n) reaction with bombarding energies around 50 MeV have been studied usingγ-ray spectroscopic techniques. Spins and parities have been assigned on the basis of angular distribution andγ-ray linear polarization measurements. States with spins up to 39/2+ and excitation energies around 6 MeV have been identified. Calculations using the empirical shell model have been performed in order to assign configurations.

Lifetimes of excited states in164Hf

Lifetimes of excited states in164Hf were measured using the Doppler-shift recoil-distance method. Gamma-gamma coincidences at eleven target-stopper distances were measured using the twelve Compton-suppressed Ge-detectors of the OSIRIS spectrometer. From the coincidence spectra the intensities of the Doppler-shifted and unshiftedγ-lines were determined. The quadrupole momentsQtof transitions within the rotational bands derived from the lifetimes are constant within the experimental uncertainties up to the 18+ state. TheQtvalue for the transition between the ground- and the neutroni132/2 band (s-band) which is strongly reduced compared to the values of the in-band transitions is used to deduce a band interaction energy of 34 keV ≦V≦57 keV.