Fragments produced in binary splits of an excited projectile-like fragment (PLF${}^{*}$) formed in the reactions ${}^{124}$Xe $+$ ${}^{112,124}$Sn at an incident energy of 50 MeV/$A$ are examined. The dependence of the isotopic composition of light fragments ($4⩽Z_L⩽8$) on rotation angle allows one to explore changes in $N/Z$ on the time scale of the rotational period of the PLF${}^{*}$. Changes in the $N/Z$ of the fragments persist for times as long as 2–3 zs (600–900 fm/$c$). The two-component nature of the time dependence of $\langle N\rangle /Z$ for $Z_L=4$ and the $Z$ dependence are related to differences in the initial configurations and subsequent decay of the PLF${}^{*}$.

• Received 27 April 2012

DOI:https://doi.org/10.1103/PhysRevC.86.021603