Resonant modes in the nuclear medium and nucleus-nucleus collisions

The properties of the Delta-resonance are investigated in infinite nuclear matter, in the semi-infinite slab model and in charge exchange reactions on a finite nucleus. Also nuclear fragmentation and interferometry experiments have been analysed. In infinite nuclear matter the decay of the Δ-resonance into a nucleon and a general spin-isospin mode consisting of pions (ρ-mesons), NN-1 and ΔN-1 states is calculated. For the case of no width of the Δs in the spin-isospin mode, partial contributions to the Δ-width from different Δ-decay channels are presented. The decay of the spin-isospin mode at a nuclear surface is studied, taking into account the in-medium properties of the Δ. In the semi-infinite slab model the contributions to the total surface response from different decay channels NN, Nπ,π in (p,n) and (3He,T) reactions, are calculated. Good qualitative agreement with recent exclusive experiments is achieved. The Δ-nucleus optical potential from microscopic calculations in nuclear matter is used to study the effects of its energy dependence in (p,n) and (3He,T) reactions. The neutron or triton spectrum is calculated via response function of a finite nucleus. Only very small effects, 1-2%, were found for the (3He,T) reaction. The emission of low energy (1A to 6A MeV) medium size (Z=3-12) fragments in 16O+37Al reactions at 94A MeV, has been studied. The numerical implementation normally used to simulate the BUU equation has been used to construct a more classical cascade model that could also give fragment distributions. With this model the gross features of the experimental data have been reproduced. Small angle pp-, nn- and pn-correlation functions from 30A 40Ar+197Au reactions have been studied using evaporation, BUU and BUU+evaporation as sources for generating 'free' particles. Also here the gross features were reproduced. 32 refs