Isospin diffusion and equilibration for Sn + Sn collisions at E/A = 35 MeV

Equilibration and equilibration rates have been measured by colliding Sn nuclei with different isospin asymmetries at beam energies of E/A = 35 MeV. Using the yields of mirror nuclei of (7)Li and (7)Be, we have studied the diffusion of isospin asymmetry by combining data from asymmetric (112)Sn + (124)Sn and (124)Sn + (112)Sn collisions with those from symmetric (112)Sn + (112)Sn and (124)Sn + (124)Sn collisions. We use these measurements to probe isospin equilibration in central collisions where nucleon-nucleon collisions are strongly blocked by the Pauli exclusion principle. The results are consistent with transport theoretical calculations that predict a degree of transparency in these collisions, but inconsistent with the emission of intermediate mass fragments by a single chemically equilibrated source. Comparisons with quantum molecular dynamics calculations are consistent with results obtained at higher incident energies that provide constraints on the density dependence of the symmetry energy.