Isospin Dependence of Preequilibrium Nucleon Emission in Intermediate Energy Heavy Ion Collision

The isospin dependence of preequilibrium nucleon emission for the neutron deficient colliding system and neutron rich system has been studied in the wide beam energy region. The calculation results show that the ratio of preequilibrium emission neutrons to protons is sensitive to the symmetrical potential and insensitive to the isospin dependence of in medium nucleonnucleon collision cross section from low beam energy region to high energy region, in which nucleonnucleon collision dynamics is dominant, namely the isospin dependence of in medium nucleonnucleon cross section excites neutron and proton to be emitted with about the same probability in wide beam energy region. At the same time, the neutrons and protons are excited to be emitted with the same probability for Pauli potential, momentum dependence interaction and impact parameter, even though their effects on preequilibrium neutron number and proton number are obvious. The ratio of preequilibrium neutrons to protons for neutron rich colliding system is larger than the initial value of neutron proton ratio of colliding system, but that for neutron deficient system is less than the initial value. In this case, one can compare the theoretical results with the experimental data systematically to extract information on the symmetrical potential.