A microscopic cranking model for nuclear collective rotation I: rigid-plus-irrotational-flow rotating frame

Abstract

We derive in a simple manner and from first principles the Inglis semi-classical phenomenological cranking model for nuclear collective rotation. The derivation transforms the nuclear Schrodinger equation (instead of the Hamiltonian) to a rotating frame using a product wavefunction and imposing no constraints on either the wavefunction or the nucleon motion. The difference from Inglis model is that the frame rotation is driven by the motions of the nucleons and not externally. Consequently, the transformed Schrodinger equation is time-reversal invariant, and the total angular momentum is the sum of those of the intrinsic system and rotating frame. In this article, we choose the rotation of the frame to be given by a combination of rigid and irrotational flows. The dynamic angular velocity of the rotating frame is determined by the angular momentum of the frame and by a moment of inertia that is determined by the nature of the flow combination. The intrinsic-system and rotating-frame angular momenta emerge to have opposite signs. The angular momentum of the rotating frame is determined from requiring the expectation of the total angular momentum to have a given value. The transformed Schrodinger equation has, in addition to the Coriolis energy term, a rigid-flow type kinetic energy term that is absent from the conventional cranking model Schrodinger equation. Ignoring the relatively small effect of the fluctuations in the angular velocity and for a self-consistent deformed harmonic oscillator mean-field potential, the resulting Schrodinger equation is solved for the ground-state rotational band excitation energy and quadrupole moment in different configurations of Ne-20 and the results are compared with those of the conventional cranking model and empirical data.