A. Alderson

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 Rotational bands, characteristic of a superdeformed prolate shape ( e ≈0.6) and extending to above spin 60 h , have been observed in both 150 Gd and 151 Tb. The magnitudes of the moments of inertia I (2) were found to vary with frequency and the variation greatly exceeded that seen in 148,149 Gd and 151,152 Dy. The differences in the I (2) s are attributed to the occupation of particular high- N orbitals. Moreover, contrary to the previous examples the bands in both 150 Gd and 151 Tb de-excited at a much higher rotational frequency of h ω≈0.4 MeV and this may indicate that the pair gap extends to higher frequencies in 150 Gd and 151 Tb.

Hg and Their Dynamical Moments of Inertia

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.

Superdeformed bands in 150Gd and 151Tb: Evidence for the influence of high-N intruder states at large deformations

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

Abstract The g -factor of the K = I =25 isomer in 182 Os has been measured by observing the angular precession of the decay γ-ray angular distribution in an external magnetic field as g =+0.425 (8). This result is compared with predictions based on experimental g -factors of single-particle Nilsson orbitals in this mass region.

The Quadrupole Moment of the K = 25 Isomer in

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.

^182

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.

Os

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.

The g-factor of the K=25 isomer in 182Os

Abstract High spin states in 161 Er and 162 Er have been populated using the 130 Te + 36 S reaction at a bombarding energy of 170 MeV. In 161 Er, three rotational bands were extended from I≈35ħ to I≈50ħ. In 162 Er the positive parity yrast band was observed to I=44ħ. These rotational sequences are compared to a simple unpaired model which was successful in predicting the behaviour of similar high spin data on 159,160 Er. These studies of the light Er isotopes constitute the highest spins observed in normal deformed nuclei and yield direct and specific information on the single-neutron spectrum of states.