Isospin dependence of preequilibrium nucleon emission in intermediate energy heavy ion collision

The isospin dependence of preequilibrium nucleon emission for the neutron-d eficient colliding system and neutron-rich system has been studied in the w ide beam energy region. The calculation results show that the ratio of pree quilibrium emission neutrons to protons is sensitive to the symmetrical pot ential and insensitive to the isospin dependence of in-medium nucleonnucleo n collision cross section from low beam energy region to high energy region , in which nucleonnucleon collision dynamics is dominant, namely the isospi n dependence of in-medium nucleonnucleon cross section excites neutron and proton to be emitted with about the same probability in wide beam energy re gion. At the same time, the neutrons and protons are excited to be emitted with the same probability for Pauli potential, momentum dependence interact ion and impact parameter, even though their effects on preequilibrium neutr on number and proton number are obvious. The ratio of preequilibrium neutro ns to protons for neutron-rich colliding system is larger than the initial value of neutron-proton ratio of colliding system, but that for neutron-def icient system is less than the initial value. In this case, one can compare the theoretical results with the experimental data systematically to extra ct information on the symmetrical potential.