Phase-Space Exploration in Nuclear Giant Resonance Decay

The rate of phase-space exploration in the decay of isovector and isoscalar giant quadrupole resonances in $^{40}$Ca is analyzed. The study is based on the time dependence of the survival probability and of the spectrum of generalized entropies evaluated in the space of 1p-1h and 2p-2h states. If the 2p-2h background shows the characteristics typical for chaotic systems, the isovector excitation evolves almost statistically while the isoscalar excitation remains largely localized, even though it penetrates the whole available phase space.