Z. W. Grabowski

Observation of superdeformation in 191Hg.

The first observation of superdeformation in the A {approx equal} 190 mass region is reported. A rotational band of 12 transitions with an average energy spacing of 37 keV, an average moment of inertia of 110 {Dirac h}{sup 2} MeV{sup {minus}1}, and an average quadrupole moment of 18 {plus minus} 3 eb has been observed in {sup 191}Hg. These results are in excellent agreement with a calculation that predicts an ellipsoidal axis ratio of 1.65:1 for the superdeformed shape in this nucleus. Evidence for another discrete superdeformed band and superdeformed structures in the quasi-continuum was also found in the data. 19 refs., 6 figs.

Multiple band structures in 191Hg

Abstract The level structure of the nucleus 191Hg has been considerably extended from previous studies by using the 160Gd(36S, 5n) reaction in conjunction with an array of Compton-suppressed germanium detectors. A series of 13 different level sequences has been established in addition to three superdeformed bands. A majority of the band structures can be understood in cranked shell model calculations assuming an oblate collective nuclear shape. There is some evidence for the onset of triaxiality. Finally, two bands of single-particle character have been found. They are interpreted as being associated with a prolate non-collective shape (γ = −120°).

Aligned νi132 bands coupled to different shapes in 186Hg

Abstract The structure of 186Hg has been studied through the 156Gd(34S, 4n) reaction. Three bands with even spin and parity are observed; two of them are established up to high spin and are found to cross with little interaction at I= 16+. Cranked shell model calculations suggest that these two bands can be associated with a decoupled ν i 13 2 pair based on a prolate and on an oblate or triaxial shape, respectively.

Lifetime measurements of terminating and collective high-spin states in 155DY and 156DY

Abstract Lifetime measurements for the isotopes 155 Dy and 156 Dy have been extended up to spins around 40ħ by the Doppler shift attenuation method in conjunction with γ-γ-coincidence measurements. Results have been obtained for the yrast band in 156 Dy and for three bands in 155 Dy. Strong retardations of the E2-strengt were observed for intruding terminating sequences, for which specific single particle configurations are suggested.

Level structure of 148Gd up to I=44☆

Abstract The level scheme of 148Gd has been extended to I=44 by use of a Compton-suppressed Ge spectrometer array. Up to I=38 the observed level spectrum consists of spherical and oblate states of aligned-particle type. A change in structure along the yrast line is indicated at higher spins, where fast E2 transitions suggest the onset of collectivity.

Yrast excitations in A = 126–131 Te nuclei from deep inelastic 130Te+64Ni reactions

Abstract Thick target γγ coincidence measurements for the system 130 Te + 275 MeV 64 Ni have been performed using the GASP Ge detector array at Legnaro. For the isotopic assignments of previously unknown γ-ray cascades, prompt γγ coincidences observed between Te and Ni partner products were of vital importance. The results yield much new information about excited states of moderate spins in A = 126–131 tellurium nuclei, especially about yrast excitations of the little studied odd- A isotopes 127 Te, 129 Te, and 131 Te. Level systematics of tellurium nuclei are presented, and both single-particle and collective aspects of the level spectra are discussed.

Coulomb excitation of vibrational-like states in 166−170Er

Abstract Direct E2 and E3 Coulomb excitation of 2+ and 3− states with 14 MeV 4He ions on isotopically enriched targets of 166Er, 168Er and 170Er has been measured by means of γ-ray spectroscopy. Several 2+ states and 3− octupole vibrational states were identified in each nucleus. The B(Eλ, 0 → J = λ) is obtained for excitation of each state, and information is given on the reduced transition probabilities for the different decay modes of these states. The experimental results are compared with theoretical predictions of nuclear models describing these states.

Nuclearg-factors of the 328 keV state in194Pt, the 240 keV state in195Pt, and the 356 keV state in196Pt determined by recoil-implantation into iron and cobalt hosts

The iron-implantation-perturbed-angular-correlation technique (IMPACT) has been used to measure the Larmor precessions of the 328, 240, and 356 keV states of194Pt,195Pt, and196Pt nuclei, respectively, in ferromagnetic iron and cobalt hosts. The observed angular precessions in iron, corrected for the transient field effect, wereω τ194(328)=0.103±0.006 rad,ω τ195 (240)=0.142±0.012, andω τ196(356)=0.084±0.010. For cobalt hosts, the observed Larmor precessions were ω τ194(328)=0.068±0.006, ω τ195(240)=0.096±0.012, andω τ196(356)=0.057±0.013. Agreement between theg-factors obtained from the measurements in iron hosts and the measurements in cobalt hosts is very good, and a weighted average of the two measurements givesg194(328)=0.349±0.031,g195 (240)=0.136±0.013, andg196(356)=0.329±0.039.

Angular correlation studies in 144Nd

Abstract The decays of 144Pr and 144Pm populate ten excited states in 144Nd. We have carried out detailed γγ angular correlation measurements in order to establish spin assignments for these levels. The measurements were performed with Ge(Li)-Ge(Li) and NaI(Tl)-Ge(Li) systems. Eleven sets of A22 and A44 values were obtained. The Jπ assignments for levels in 144Nd (level energies in keV) are as follows: g.s.,0+; 696, 2+; 1314, 4+ ; 1511, 3−; 1561, 2+ ; 1791, 6+; 2084, 2+ ; 2093, 5−; 2186, 1−; 2204, 4; 2644, 1. Mixing ratios were determined for six γ-transitions.

Differential lifetime measurements and configuration-dependent quadrupole moments for superdeformed bands in nuclei near 152Dy☆

Abstract High-precision lifetime measurements have been performed in superdeformed (SD) bands of 151,152 Dy and 151 Tb with the Doppler-shift attenuation method. Differences found in the quadrupole moments Q 0 of the yrast SD bands are understood in terms of shape polarization effects by the high- N intruder orbitals. Q 0 moments are also presented for three excited SD bands in 151 Dy. Recent calculations can account for most of the observations.