EXPERIMENTAL EVIDENCE FOR SHAPE CHANGES AT HIGH SPIN

Abstract

Publisher Summary This chapter presents experimental evidence obtained with TESSA for shape changes at high spin. Continuum γ-ray spectroscopy data indicates the co-existence of both prolate and oblate shapes in ν = 90 nuclei and lifetime data in 152Dy shows that the super-deformed decays are enhanced. The chapter reviews experimental evidence for various shape changes in some dysprosium, erbium, and ytterbium nuclei. There is strong evidence that ν = 88 isotones show a rapid change in shape around a spin of 30 ħ. The quasi-vibrational spectrum can be interpreted as a gradual change to an oblate shape, possibly involving band terminations. However, such a feature should be accompanied by stretched dipoles, and there is some evidence for this from the internal conversion probabilities but it is not corroborated by other data. At higher spins, the continuum data indicate that these nuclei again show collective rotational structure as expected from a prolate rotor. Evidence for this shape change has been obtained by an experiment using TESSA in which a narrow ridge is observed. Observation of a super-deformed ridge for the shape change in 152Dy has been confirmed, and it has been shown to be composed of enhanced collective E2 transitions, providing conclusive evidence of its super-deformed origin.