Excitation energy of a free fermi gas in the (n, 2n) channel

Abstract

Fast neutron induced (n, 2n) cross sections are estimated in the framework of the free gas model. Since the observed excitation energy is measured from the effective Fermi surface of a real nucleus, a distinction is made between the model excitation energy and the experimentally observed excitation energy of a system. By removing the interactions in an actual nucleus, one can go over to the hypothetical free gas reference system. The interaction energies of a real system will then contribute to the total excitation energy of the free gas system. When nuclei with the same experimentally observed excitation energy are compared, the model excitation energies are altered depending on the nuclear interactions. These interaction energies change the observed excitation to the model excitation energy and convert a real system into a free gas system at matched excitation energies. The view point is used here to obtain quantitative estimates of the fast (n, 2n) cross sections at 6 MeV residual excitation. The calculations agree fairly well with the experimental results. The limitations of the present view point are discussed.