I. Ali

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

Abstract The nucleus 198 Pb was populated via the 186 W( 17 O,5n) 198 Pb reaction at beam energies of 92 and 98 MeV. A highly regular rotational ΔI =1 band has been found. Angular correlation measurements confirm the transitions to be dipoles. Assuming M1 multipolarity for these transitions the experimental data are interpreted in terms of a π([505] 9 2 − ⊗[606] 13 2 + ) K π =11 − ⊗ν( i 13 2 ) 2 configuration of oblate shape. This is the first such collective oblate structure identified in the A ∼200 mass region.

Hg and Their Dynamical Moments of Inertia

Abstract The nucleus 198 Pb was populated via the 186 W( 17 O, 5n) 198 Pb reaction at beam energies of 92 and 98 MeV. Five collective rotational cascades of ΔI = 1 transitions have been found. Four are highly regular, one much more irregular. The structures are incorporated into a level scheme which extends up to approximately spin 32ħ and an excitation energy of about 10 MeV. Angular correlation measurements confirm the dipole character of the interband transitions. Their M1 multipolarity is inferred, and from this supposition the experimental data are interpreted in terms of oblate high- K two quasiproton configurations coupled to aligned neutron excitations. This interpretation is extended to include other ΔI = 1 oblate structures observed in 194–201 Pb. It is shown that the pattern of observed moments of inertia can be understood in the simple unpaired picture involving neutron i 13 2 excitations. The identical bands observed are interpreted in terms of the normal-parity weakly-coupled singlet orbital.

First observation of a collective dipole rotational band in the A∼200 mass region

Abstract A Doppler shift attenuation measurement has been carried out to determine the collectivity of the superdeformed band in 150 Gd. The data was found to be consistent with a constant inband quadrupole moment of 17 ± 3 e b. This corresponds to a quadrupole deformation of s 2 ≈0.58. In addition the measurement has resolved important questions regarding the de-excitation of the band, confirming the rapid de-excitation of the superdeformed band in 150 Gd with more than 80% of the band intensity being lost over one transition.

Collective oblate dipole rotational bands in 198Pb

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.

The collectivity and the de-excitation of the yrast superdeformed band in 150Gd

The 196Pb nucleus was populated via the 184W(16O,4n)196Pb and 186W(16O,6n)196Pb reactions at beam energies of 98 MeV and 120 MeV, respectively. A new Delta I=1 magnetic dipole band has been observed. This band is believed to be built on a collective oblate configuration involving high-K proton orbitals coupled to two rotationally aligned i13/2 neutrons. The previously observed 196Pb superdeformed band was also populated in these reactions.

The Quadrupole Moment of the K = 25 Isomer in

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-.

^182

The nucleus197Pb was populated via the186W(17O,6n)197Pb reaction at beam energies of 98 and 110 MeV. Two regular ΔI=1 bands of magnetic dipole transitions have been found. Possible interpretations in terms of collective oblate configurations involving high-K proton orbitals coupled to three i13/2neutrons are discussed. The similarities between several of the bands discovered in197–200pbnuclei are emphasized.

Os

High spin states in 161Er and 162Er have been populated using the 130Te+36S reaction at a 36S bombarding energy of 170 MeV. In 161Er, three rotational bands were extended from I approximately=35 h(cross) to I approximately=50 h(cross). In 162Er the lowest energy positive parity band was observed to I=44 h(cross) and two negative parity bands to I approximately=32 h(cross). The behaviour of these rotational sequences are explained in terms of the expected spectrum of single neutron states in the absence of static neutron pair correlations.

Coexistence of Collective Oblate and Superdeformed Prolate Shapes 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.