Superdeformed nuclei

A special class of quantum rotors are the superdeformed nuclei. The moments of inertia, after scaling by A5//3, are all similar due to the fact that the shape of these nuclei is largely independent of mass with an axis ratio of 2 1 due to shell stabilization effects discussed below. 

Nuclei can be trapped in the secondary minimum of the fission barrier. Such trapped nuclei will experience a significant hindrance of their y-ray decay back to the ground state (because of the large shape change involved) and an enhancement of their decay by spontaneous fission (due to the thinner barrier they would have to penetrate.) Such nuclei are called spontaneously fissioning isomers, and they were first observed in 1962 and are discussed below. They are members of a general class of nuclei, called superdeformed nuclei, that have shapes with axes ratios of 2 1. These nuclei are all trapped in a pocket in the potential energy surface due to a shell effect at this deformation. 

Raychev etal. [24] have shown that good fits can be obtained for nuclear rotational spectra of even-even rare earths as well as actinide elements by using Eq. (22). Furthermore, it has been shown [25]-[28] that Eq. (22) may also give a good description of such effects as backbending and staggering in rotational spectra of superdeformed nuclei and diatomic molecules as well. It can be seen that Eq. (21) fails in describing such spectra. 

Several years ago it was discovered that sequences of states in rotational bands of superdeformed nuclei, e.g. " Gd [1], [2], [3], diyrast band of... 

Blann, M. Decay of deformed and superdeformed nuclei formed in heavy ion reactions. Phys. Rev. C21, 1770-1782 (1980)... 

A nucleus is called superdeformed or hyperdeformed in states in which the ratio of its axes is approximately 2 or 3, respectively. 

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