Nuclear intrinsic vorticity and its coupling to global rotations

Important collective modes which are generally neglected within current descriptions of nuclear excitations in terms of fluid dynamics, are studied here. The intrinsic vortical modes are defined in a general way from which a specific mode, both simple and versatile enough, is particularly discussed. In this paper the main emphasis is made on the coupling of the chosen intrinsic mode to the rotation of the nuclear principal axes frame with respect to the laboratory system. A semi-quantal description of such excitations is proposed which is a generalization of the so-called routhian approach of global rotations. The results of a semiclassical treatment of the corresponding variational problem are presented. A simple mean field approach where the one-body potential is mocked up by a harmonic oscillator is discussed in a somewhat detailed fashion. The broad range of validity of a quadratic approximation for the collective energy in terms of the relevant angular velocities, is hinted from the previous simple model approach. Some general consequences of the latter are then drawn which have bearing on some possible fingerprints for the existence of such excitations, as the staggering phenomenon observed in gamma transition energies in some superdeformed states and the occurrence of identical rotational bands in neighbouring nuclei. (C) 1997 Elsevier Science B.V.