C.A. Kalfas

Spin ∼60 ℏ in 156Dy: competition between collective and terminating structures at very high-spin

AbstractThe highest-spin discrete states x0e.I;60 and E ;30 MeV in normal deformed nuclei have been observed in the x rare-earth isotope Dy using the Sn S,4n reaction in conjunction with the GAMMASPHERE spectrometer. The 156 124 x0e 36 .positive parity yrast sequence appears to evolve smoothly from a prolate collective towards an oblate non-collectivex0e. x0e .shape, in contrast to the sudden shape change observed in the isotone 158 Er. Terminating states are identified in the negativeparity sequences at I p s52 y and 53 y and specific multi-particle-hole configurations are assigned by comparison withcranked Nilsson-Strutinsky calculations. An order of magnitude increase in the interaction strength between close lyinghigh-spin weakly collective structures is determined compared with that found in the lower-spin strongly collective domain.These results give valuable insight into the interplay between collective and terminating structures, and their competition foryrast status in the 40y60 spin range. q1998 Elsevier Science B.V. All rights reserved.

Highly excited Delta I=1 structures in 193Hg

Highly excited states in the nucleus 193Hg have been investigated by in-beam gamma -ray spectroscopic techniques using the EUROGAM array. The reaction 150Nd(48Ca,5n) at a beam energy of 213 MeV was used to populate states of 193Hg. The level scheme has been considerably extended (up to 10.7 MeV) and enriched from earlier studies. Two new structures of competing dipole and quadrupole transitions were observed. Experimental B(M1)/B(E2) ratios were determined for the two structures and compared with theoretical estimates. They were also compared with similar structures in the neighbouring Hg and Pb nuclei.

The N = 7 unfavoured superdeformed band in 193Hg; coriolis splitting and neutron shell structure at extreme deformation

A new superdeformed band is reported in 193Hg which has properties that are consistent with it being based on the unfavoured N = 7 (π, α) = (−, +12) intruder orbital. The signature splitting at hω = 200 keV of this intruder orbital and its favoured (−, −12) partner is estimated to be 160±30 keV, which is in agreement with cranked mean field calculations. This band completes the set of low-lying quasi-neutron orbitals predicted to be at the N = 113 superdeformed Fermi-surface. The previously known superdeformed bands in 193Hg have been extended to higher rotational frequencies, hω ⩾ 0.40 MeV.

Exploring the I = 50-60 hbar domain: collective and terminating structures in 156Dy, 159Er and 160Er

Very high spin (50-) states in transitional , and nuclei have been studied using the GAMMASPHERE and EUROGAM -ray spectrometers. The lowest energy positive-parity bands in are found to evolve smoothly towards an oblate shape in contrast to the sudden change observed in the neighbouring nucleus. In , the decay path of the positive-parity yrast band splits above and favoured multi-particle-hole states are identified in the irregular pattern at and . The yrast structure of is found to remain collective up to and beyond with no sign of an apparent termination.

High spin structures in 194 Hg

High spin states in the isotope194Hg were populated using the150Nd (48Ca,4n) reaction at a beam energy of 213 MeV. The analysis ofγ-γ coincidences has revealed two new structures at excitation energies above 6 MeV and at moderate spin. The two structures are a manifestation of the deviation of nucleus from the collective rotation which dominates its lower excitation behaviour. A comparison with similar structures in the neighbouring Hg isotopes is also attempted.

High spin levels in119Te

High spin levels in119Te have been populated following the96Zr (30Si, α 3n)119Te reaction at a beam energy of 135 MeV. The subsequentγ-ray deexcitation was studied usingγ-ray spectroscopic methods. New levels and several spin and parity assignments up toJπ=55/2− were established. The decay scheme at high-spin exhibits single-particle characteristics associated with the fully aligned ν(h11/2)3 π(g7/2)2 configuration for the 39/2− level, while the 55/2− level could be interpreted as fully aligned π(d5/2)2ν h112/5 g72/−2) configuration.