Orientation fluctuations and the angular distribution of the giant-dipole-resonance γ rays in hot rotating nuclei

A recent macroscopic approach to the giant dipole resonances in hot rotating nuclei is extended to include the angular distributions of the γ rays emitted in the resonance decay. It provides a uniform description of thermal fluctuations in all quadrupole shape degrees of freedom within the framework of the Landau theory. In particular, the inclusion of fluctuations in the nuclear orientation with respect to the rotation axis is crucial in reproducing the observed attenuation of the angular anisotropy. The theory is applied to recent precision measurements in ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ and ${}_{}{}^{92}{}_{}{}^{}\mathrm{Mo}$ and is the first to reproduce well both the observed giant-dipole-resonance cross sections and the angular anisotropies.