Chaos and damped collective motions in highly excited nuclei

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In the present research, we investigated the damping of rotational motion in nuclei at very high spin and at finite but moderate temperature. Especially, we focused on studies to clarify a relation between the rotational damping phenomena and the formation of compound states, which is one of the most basic features in the highly excited nuclei.The compound damping width is a dynamical measure of complexity of the wavefunctions of highly excited levels. We clarified that this quantity emerges as a two-component structure in the energy correlation spectra of quasi-continuum gamma rays associated with the damped rotational motion. This points out for the first time a possibility of probing the compound damping width in the experiments.We also studied the systematics of the rotational damping phenomena, clarifying a significant mass number dependence associated with a shell structure effect. An analysis of recent experimental data is also performed.A new method is proposed to analyze in a general manner fluctuations and fine structures in the strength function associated with the damped collective motions. For this purpose, we introduced a new concept of the local scaling dimension, and demonstrated its applicability for some examples.