I. Jenkins

The competition between collective and single particle behaviour in the odd-odd isotopes 128,130La

Excited states in the odd-odd nuclei 128,130La have been investigated to high spin using gamma -ray spectroscopy. Two distinct bands are seen, one based on a pi h11/2(X) nu h11/2 structure and the other on a pi h11/2(X) nu g7/2 configuration. Backbends are observed in both configurations for both nuclei and the nature of the particles responsible can be conclusively proved. Experimental variation in the energy-level signature splitting and B(M1)/B(E2) ratios are discussed in terms of the polarising effects of the odd proton and odd neutron on the soft collective core. The results are discussed in terms of the cranked shell model, odd-odd particle-rotor calculations and total Routhian surface calculations. They are also compared to neighbouring odd and odd-odd systems.

Prolate and oblate rotational bands in 136Sm

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.

Spectroscopy of the light rare-Earth nuclei 133Pm and 133Sm: Configuration-dependent pairing and evidence for strong residual proton-neutron interactions in neighbouring odd-N and odd-Z nuclei

Abstract The low-lying, rotational band structures of the highly neutron-deficient light rare-earth nuclei, 133Sm and 133Pm have been investigated using the 40Ca + 96Ru reaction at a beam energy of approximately 180 MeV. Five new bands have been observed in both nuclei. 133Sm possesss two strongly coupled bands which are thought to be built upon the v h 11 2 [523] 7 2 − and v d 5 2 [402] 5 2 + Nilsson configurations. In addition to the previously reported v i 13 2 intruder band, there is also evidence for a second decoupled, negative-parity structure in 133Sm based on the v h 9 2 [541] 1 2 − orbital. In 133Pm evidence is presented for both signature partners of the π h 11 2 band. The expected h 11 2 neutron alignment in these bands has not been observed. It is suggested that this provides evidence for a strong pn interaction. A strongly coupled band built on the π g 7 2 [413] 5 2 + configuration has also been established. Both signature partners of this band show clear evidence for the alignment of a pair of h 11 2 protons followed by a pair of h 11 2 neutrons. A strongly coupled three quasi-particle configuration has also been identified which feeds into the unfavoured signature of the π h 11 2 band. The results are discussed in terms of cranked shell model, total routhian surface calculations and the systematics of the A ∼ 135 region.

The proton structure of the superdeformed bands in the N=73 isotones 130La, 131Ce and 133Nd

A superdeformed band has been identified in the odd-odd nucleus 130La. The nine transitions seen show a behaviour consistent with the deformation epsilon -0.4 corresponding to a prolate rotor with a 3:2 axis ratio. The behaviour of the moments of inertia in the superdeformed bands in the N=73 isotones 130La, 131Ce and 133Nd is discussed in terms of a few particles in high-N shells.

A superdeformed band in131Ce

A rotational band of 16γ-rays has been found in131Ce with a high moment of inertia indicating a deformation ε2∼0.38 and extending to spin ∼40ħ. Its intensity is ∼∼5% of the total in131Ce, confirming a difference in the intensity systematics for superdeformed states in Ce nuclei compared with Nd.

Yrast band spectroscopy of132Sm and130Nd

The states in the yrast band of132 Sm have been identified for the first time up to Jπ=16+. The yrast band of130Nd has also been extended from Jπ=16+ to 24+. The energy of the first 2+ state in132Sm indicates that the quadrupole deformation ε2 ∼ 0.3 and is still increasing as the neutron number N decreases across the samarium isotopes. The results for130Nd allow the (h2/11)2 proton crossing frequency to be determined as ω=0.325 ± 0.005 MeV/ħ. This result is compared with cranked shell model predictions.

Band structures in134Nd

The decay scheme for134Nd has been extended to high spin and a new negative parity band discovered. These results are discussed in terms of particle alignments.

Evidence for an i13/2 neutron band in133Sm

A rotational band of nine γ-rays has been observed in133Sm. The moment of inertia of the band indicates that it has a higher deformation than expected for states in nuclei in this region. The properties are such that it can be interpreted as being due to the odd neutron occupying the ν i2/13 nn intruder orbital. This is the first evidence for the occupation of this orbital in nuclei with neutron number N<73.