Mean field and effective cross sections in hot nuclei

Abstract

Collisions between heavy nuclei produce nuclear matter of high density and excitation. Brueckner methods are used to calculate the momentum- and temperature-dependent mean field for nucleons propagating through nuclear matter during these collisions. The use of a potential model for the NN interactions is bypassed by calculating the Brueckner reaction matrix directly from the NN phase shifts using a version of Brueckner theory previously published by the author. Arndt phase-shift solutions up to 1600 MeV in energy are used. The binding energy of nuclear matter is normalized to −15.5 MeV by adjusting one free parameter. This gives a saturation density of 0.16 fm −3 and the compressibility is 200–250 MeV. The temperature and density dependence of the effective interaction is shown. The mean field is complex and the real part relates to “one-body” collisions while the imaginary part is related to the “two-body” collision term in transport theory. The error in using free cross-sections when calculating the imaginary part is in general less than 20% but can be at least as large as 75%. The influence of the mean field (effective mass) on the collision term is emphasized.