F. Hanna

Multiple Superdeformed Bands in

Abstract Three superdeformed bands have been observed in 194Hg. The dynamical moment of inertia J (2) of all three bands is observed to increase by 30–40% over the frequency range ħω = 0.1–0.4 MeV. This phenomena can be understood in terms of the gradual alignment of pairs of high-j intruder orbitals within the framework of the cranked Woods-Saxon and Nilsson models including pairing. The calculations together with the observed J (2) behaviour of the three bands indicate that pairing correlations in the superdeformed minimum are rather weak.

^194

High-spin states were populated in 54122Xe68 using the fusion evaporation reaction 96Zr(30Si,4n) at a beam energy of 135 MeV. The level scheme of 122Xe has been extended up to spin approximately 30h(cross). The rotational bands and band crossings in 122Xe are assigned within the framework of the cranked shell model. Three bands are found to lose their rotational character or to branch above spin approximately 20h(cross). This is interpreted as the collective rotation of a prolate nucleus being replaced by a regime of non-collective single-particle states at high spin. Single-particle configurations are suggested for the high-spin non-collective states using modified oscillator and Woods-Saxon potentials. The development of the nuclear shape is analysed employing potential energy and total Routhian surface calculations.

Hg and Their Dynamical Moments of Inertia

Abstract Discrete γ -ray transitions have been observed up to spin ∼30 in 122 Xe. A dramatic change in the mechanism by which this nucleus generates angular momentum is observed to occur above spin 20. The collective rotation of a prolate nucleus is replaced at high spin by a regime of non-collective single-particle states. Particularly favoured states are observed at high spin and by comparison with the predictions of the cranked Nilsson and Woods-Saxon models specific single-particle configurations are suggested. This gives information on the spectrum of single-particle states and the active orbitals which build high angular momentum states in this mass region.

High-spin gamma -ray spectroscopy of 122Xe

Abstract The quadrupole moment of the I = K =25 + , T 1 2 =150 ns isomer in 182 Os has been measured by observing the time-dependent quadrupole interaction pattern of the decay radiation from the isomer implanted in a single crystal of Os. The result of | Q |=4.2(2) e b is consistant with the predicted deformation of β 2 =0.2 for 182 Os at I =25 and K = I for this isomer.

Competing angular momentum mechanisms and nuclear shapes at high spin in 122Xe

Competition between single-particle and collective modes of excitation is observed in 119I at high spin. Whereas rotational states, associated with a prolate pi h11/2 orbital, are yrast for spins I<or=39/2, a noncollective oblate state is yrast at Ipi =43/2-. This state is interpreted as the fully-aligned pi (h11/2 (X) g7/22)23/2- (X) nu (h11/22)10+ configuration outside a 50114Sn64 core. Several other noncollective states are observed above this state. At the highest spins, the collective states again become yrast when a pair of h11/2 neutrons align. The rotational pi h11/2 (X)( nu h11/22) structure could be followed up to Ipi =63/2-.

The Quadrupole Moment of the K = 25 Isomer in

Abstract Three superdeformed (SD) bands have been observed in 194Hg and four (or five?) SD bands in 193Hg using the 150Nd + 48Ca reaction. All bands except for two in 193Hg show a steady increase in dynamical moment of inertia J (2) with rotational frequency. The two exceptional bands form a classical pair of strongly interacting bands. It is suggested that the strong interaction between the bands is caused by a softness to octupole deformation. Evidence is found for the existence of dipole transitions connecting bands of opposite signature in 193Hg. The strengths of these transitions suggest that they are probably E1 supporting the importance of the role of octupole vibrations. These data suggest the wider importance of octupole softness in enhancing E1 transitions in the SD feeding and decay mechanisms. The spectroscopy of the observed SD bands in 193,4Hg are discussed in detail and attention is drawn to the “identical” energies of γ-rays in these isotopes with those in lighter isotopes. The similarities in bands relate to the neutron sub-shell closure for SD nuclei at N=112.

^182

A brief reminder is given of the evidence for the existence of octupole correlations in the superdeformed shape of 193Hg. It is pointed out that comparison of the data on the superdeformed bands in 19Hg with Cranked Shell Model calculations gives firm assignments to the signatures and parities of these bands. The spin assignments obtained are in agreement with the spin assignments given by projecting the SD bands back to zero rotational frequency and assuming the intrinsic alignment i0 is zero. These spin asssignments leave ‘‘identical’’ bands in 191Hg, 193Hg and 194Hg with a surplus 1ℏ of spin relative to the superdeformed core nucleus 192Hg. This extra 1ℏ of alignment is not understood.