Isospin and Instabilities in Nuclear Matter

In this paper two different topics are discussed. The first topic concerns the collective modes of asymmetric nuclear matter. We use a model based on the Quantum-Hadro-Dynamics effective field picture of nuclear matter. We focus our attention on the effects of the interplay between scalar and vector contributions. The response functions in the isoscalar/isovector channel reveal an interesting "mirror" structure, with a close parallelism in the role respectively played by the compressibility and the symmetry energy. Moreover, almost pure neutron waves are predicted at high densities. The second part of the paper concerns the spinodal decomposition of expanding nuclear matter. The distribution of the liquid domains in the spinodal decomposition is derived. It is found that the formation of the domains can be envisaged as a stationary process. Comparison of the related distribution of the fragment size with experimental data on the nuclear multifragmentation is quite satisfactory.