Brian Bush

We present a unified theory of quadrupole shape fluctuations in highly excited rotating nuclei using the framework of the Landau Theory of shape transitions. The theory is applied to several experimental observables.

Our major application is the study of giant dipole resonances (GDRs) built on hot rotating nuclei. With only two free parameters, fixed by the ground state properties, the model reproduces well experimental GDR cross-sections and angular correlations at any temperature and spin in the 90 $\le$ A $\le$ 170 mass range for both spherical and deformed nuclei. A systematic study of the cross-section reveals that higher temperature cross-sections are dominated by large fluctuations (triaxial in particular) and are less sensitive to the equilibrium shape. To include non-adiabatic effects, we generalize our theory to describe time-dependent shape fluctuations using a stochastic approach based on the Langevin equation. This can produce motional narrowing of the resonance. Comparisons with experiments deviating from the adiabatic limit are used to determine the damping of quadrupole motion at finite temperature.

Another application of the theory is in the study of E2 quasicontinuum spectra in warm nuclei, where it predicts enhancement of the B(E2), in accord with the experiment.

Finally, we apply the fluctuation theory in improved calculations of nuclear level densities as a function of energy and spin using the static path approximation (SPA). Comparison with other calculations and experiments are made.