The influence of microscopic structures on rotational motion in nuclei

Abstract

This paper will concentrate on a study of the role and influence of microscopic structures on the properties of rotational bands in nuclei. Collective rotational features are well known in nuclei. Much of the review will discuss examples taken from experimental investigations of highly/superdeformed structures and their theoretical interpretation, which provide some of best and clearest rotational phenomena observed in nuclei. These structures have welldefined rotational properties that can be described by a collective model. The link between the deformation of these structures and the valence particle configuration has been established in many nuclei and recent experimental data are presented. Detailed investigations with new, very sensitive, instrumentation have revealed some extremely interesting and unexpected phenomena, such as the observation of identical rotational bands in neighbouring nuclei and energy staggering between adjacent states within a single band. The experimental and theoretical aspects of these new features will be discussed. The spectroscopy of highly/superdeformed structures has been studied extensively and many bands observed in a given nucleus which arise from particle-hole excitations. Measurements are now available, through the strength of magnetic dipole transitions, of the properties of specific single-particle orbitals. In the medium mass (A ∼ 60) region highly deformed states have been observed to decay by both proton and alpha emission in addition to the normal γ -decay mode. The decay widths, which are retarded for these channels, are related to the microscopic structures of the states involved. Investigations of rotational motion in exotic triaxial and hyperdeformed nuclear shapes are also reviewed. Recent work on 'smooth band termination', in medium to medium-heavy nuclei, which results when a deformed collectively rotating nucleus gradually changes from a near-prolate to a non-collective oblate shape, has revealed detailed information on the configurations responsible and the effects on the bands as the spin contribution is exhausted. The concept of 'magnetic rotation', which gives rise to regular 'rotational-like' sequences of states in nuclei that are almost spherical, is discussed. This phenomenon is also found to primarily result from microscopic effects within the nucleus. A discussion of these two latter phenomena has been included in this paper, since they provide an important contribution to the topic under review.

Mean-field description of high-spin states

“…One can find summaries of the experimental findings of the last few years in the reviews of high-spin physics, like the work of Clark and Macchiavelli [1], Ward and Fallon [2] and Wadsworth and Nolan [3]. Concerning the theoretical aspects, a recent review by Frauendorf [4] mainly addresses the problem of (point-)symmetries of the cranking Hamiltonian with respect to high-spin physics.…”

Tensor part of the Skyrme energy density functional. III. Time-odd terms at high spin

“…For the other phenomena listed above, the timeodd terms provide a correction to the dominant time-even terms that might become substantial in some cases. One such observable are the moments of inertia at high spin in superdeformed (SD) rotational bands of heavy nuclei [44][45][46]. These will be the object of our study.…”

Klein–Gordon and Dirac gyroscopes

“…As a motivation for the present work, it should be mentioned that (non-relativistic) rotational behavior is highly important in the study of molecular [8] and nuclear spectra [9]. For subnuclear structures arising in the realm of high-energy physics, a relativistic treatment should be useful.…”