Properties of hot nuclear fragments formed in multifragmentation and their astrophysical implications

Abstract

The process of nuclear multifragmentation leads to thermodynamic conditions akin to those encountered in the collapse/explosion of massive stars. Thus, the knowledge obtained from studying multifragmentation may be applied to describe matter distribution in supernova. Along these lines, the present study focuses on the symmetry energy of hot fragments produced in the multifragmentation of neutron-rich systems following collisions near the Fermi energy. The experiments consist of high-resolution mass spectrometric measurements of the isotopic and velocity distributions of heavy projectile fragments. The data were systematically compared to calculations with the Statistical Multifragmentation Model (SMM). The study indicates a gradual decrease of the symmetry energy coefficient from the standard value of ∼25MeV in the compound nucleus regime (E∗/A<2MeV) towards ∼15MeV in the bulk multifragmentation regime (E∗/A>4MeV). The isotopic distributions of the hot fragments are very wide and extend towards or beyond the neutron drip-line. These findings may have important implications to the composition and evolution of hot astrophysical environments, such as core-collapse supernova and the course of the ensuing nucleosynthesis processes, such as the r-process.