Timescale for equilibration of N/Z gradients in dinuclear systems.

Equilibration of N/Z in binary breakup of an excited and transiently deformed projectile-like fragment (PLF*), produced in peripheral collisions of 64Zn + 27Al,64Zn, 209Bi at E/A = 45 MeV, is examined. The composition of emitted light fragments (3 ≤ Z ≤ 6) changes with the decay angle of the PLF*. The most neutron-rich fragments observed are associated with a small rotation angle. A clear target dependence is observed with the largest initial N/Z correlated with the heavy, neutron-rich target. Using the rotation angle as a clock, we deduce that N/Z equilibration persists for times as long as 3-4 zs (1 zs = 1 x 10-21 s = 300 fm/c). The rate of N/Z equilibration is found to depend on the initial neutron gradient within the PLF*. [ABSTRACT FROM AUTHOR]