Collective coupling between pairing and rotational degrees of freedom within a simple model

Abstract

A simple model to study the collective coupling between pairing and rotational degrees of freedom in well-deformed even-even nuclei is proposed. It relies on the description of the effects of pairing correlations on the rotational motion in terms of intrinsic vortical currents. As a result, an expression of the rotational energy within a band is provided as a polynomial of order three in the square of the angular velocity. The coefficients of this polynomial have a well-defined analytical form and their values are determined from merely three experimental pieces of data: the energy of the first ${2}^{+}$ state, the ground-state charge quadrupole moment as deduced from $B(E2,{2}^{+}\ensuremath{\rightarrow}{0}^{+})$ measurements, and a quantity deduced from the odd-even mass differences in neighboring odd nuclei. This model is tested in 24 deformed nuclei chosen across the rare-earth and actinide regions. In spite of the very restricted input of data, and moreover which is limited to nuclear properties at zero or very low excitation energies, the agreement with the data within the yrast line is in many cases, especially in actinide nuclei, excellent up to angular momenta of the order of $30\ensuremath{\hbar}$ or more. Of course, such an approach is by construction unable to reproduce physical effects which do not result from this Coriolis antipairing (CAP) type of collective quenching of pairing correlations. This is especially the case in the rare-earth region, where a backbending effect is often observed. In such cases our model may be considered as a baseline in order to disentangle the effect of the CAP collective mode from those of other existing spectroscopic phenomena.