S.M. Mullins

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.

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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

The intrinsic quadrupole moment, Q0, of the superdeformed band in 143Eu has been extracted from nuclear lifetimes, measured in a Doppler shift attenuation method experiment. Data were collected with the NORDBALL gamma-ray spectrometer following the reaction 110Pd (37Cl, 4n) 143Eu at a beam energy of 160 MeV. A centroid shift analysis of the data was carried out, using the Braune stopping powers to model the slowing down of the recoil nuclei in the target and backing materials. This gave a value of Q0 = 13.0 ± 1.5 eb for the band. The result is in good agreement with the theoretical prediction of Total Routhian Surface calculations, and supports the assigned single particle configuration, involving occupation of both neutron and proton i132 intruder orbitals from the Nosc = 6 oscillator shell.

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

The Doppler shift attenuation method has been used to extract the mean quadruple moment of the nu i13/2 intruder band in 139Gd. From a centroid-shift analysis of the data, and using Braune stopping powers, a value for the intrinsic nuclear quadrupole moment of Q0 approximately=7.0 eb is suggested, corresponding to a deformation beta 2 approximately=0.35. Because of appreciable side-feeding into the band at each level, a lineshape analysis of the data has also been attempted, in which the time structure of the side-feeding has been allowed to vary. This analysis indicates that the side-feeding is significantly slower than the in-band cascade.

Determination of the intrinsic quadrupole moment of the superdeformed band in 143Eu

Abstract Lifetimes of low-lying states have been measured in 132 Nd and 134 Nd using the coincidenceplunger technique. The reaction 32 S+ 105 Pd was used at a bombarding energy of 152 MeV. The measurement has been performed at the NSF Daresbury using the ESSA 30 array. The differential decay-curve method (DDCM) was used to analyze the recoil-distance Doppler-shift (RDDS) data. The experimental B (E2) values in 132 Nd are well described by the predictions of the rotational model and the IBM in the O(6) limit.

Quadruple moment of the i13/2 intruder band in 139Gd

High spin states in the odd proton nucleus 129La have been investigated using the techniques of in-beam gamma -ray spectroscopy. Nine rotational bands have been observed in 129La, seven for the first time. Various band crossings were observed at rotational frequencies in the range h(cross) omega =0.28-0.57 MeV. The data are mainly discussed within the framework of the cranked shell model. The rotational bands are assigned quasiparticle configurations originating from pi h11/2, pi g7/2, pi (h11/2)2(X) pi g7/2 and pi 11/2 (X) nu (h11/2g7/2) states, respectively. Four of the band crossings are thought to be associated with the rotational alignments of the first pair of h11/2 neutrons or protons.

Lifetimes of low-lying states in 132Nd and 134Nd

Six rotational bands have been established in 136Sm following heavy-ion induced reactions carried out at the Nuclear Structure Facility, Daresbury. The yrast band has been observed up to Ipi =(24+) and undergoes three band-crossings. A band was observed built on the low-lying 2+ gamma-vibrational state, in addition to two negative parity sidebands built on two-quasiproton excitations. A dipole band showing the characteristics of collective oblate rotation was also established. The results are discussed in terms of total Routhian surface and cranked Woods-Saxon model calculations.

Rotational band structures in 129La

The level scheme of143Eu has been extended to I=75/2 in an experiment with the NORDBALL Compton-suppressed Ge detector array and the110Pd(37Cl, 4n) reaction. Most of the scheme shows irregular structure of multiparticle excitations. A strongly populated straight cascade of more than 10 stretched E2 transitions suggests the onset of collectivity.

Prolate and oblate rotational bands in 136Sm

A mean lifetime measurement has been carried out on the states in the superdeformed band found in 131Ce using the Doppler shift attenuation method (DSAM). The measured intrinsic nuclear quadrupole moment is Q0 approximately=6 eb, assuming constant deformation, which corresponds to a quadrupole deformation beta 2 approximately=0.35. This is considerably smaller than the value deduced for 132Ce.