A CONTINUUM SHELL-MODEL FOR THE OPEN QUANTUM-MECHANICAL NUCLEAR SYSTEM

In this paper we consider the evolution of an open quantum mechanical system which together with its environment forms a closed system. The numerical calculations are performed for the nuclear system at low as well as at high level density. In each case, the relevant modes are discussed and compared to the results of the standard methods developed for their description. The influence of the respective remaining modes is compared with existing experimental data. The transition from the resonance reaction mechanism at low level density to the direct reaction mechanism at high level density takes place at a stochasticity threshold. The many-body properties are conserved, at high level density, in long-lived traps, but the spectroscopic information is lost. The evolution to the thermal equilibrium takes place via the formation of quantum chaos in accordance with the second law of thermodynamics. The evolution is accompanied, in the open system, by the formation of a new order with less degrees of freedom. These modes are far from thermal equilibrium. They screen the long-lived modes which are near to thermal equilibrium.