In this paper, stretching of nuclei is microscopically interpreted via the fermion dynamical symmetry model. A four-parameter energy formula with stretching for the yrast band of deformed nuclei is derived. This formula can account for the states in the yrast band below backbending and with the ratio ${\mathit{R}}_4$=E($4^{+}$)/E($2^{+}$)>0.32 in the rare earths and the actinides. It is also shown that stretching can improve the B(E2) fits in the rare earths as well. However, analyses of the fitted parameters reveal that the smooth increase of the moment of inertia and the enhancement of the B(E2)’s at low spins appear to be a more complicated phenomenon, thus suggesting the necessity to further microscopically understand these low-spin behaviors.

• Received 19 October 1990

DOI:https://doi.org/10.1103/PhysRevC.43.2224