Effect of a steep gradient in the potential energy surface on nucleon exchange

Mass number, atomic number, energy, and angular distributions were measured for the projectile-like fragments from the reaction ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ ${+}^{40}$Ca at $E_{\mathrm{lab}}$=340 MeV. General features of this reaction are compared to other mass asymmetric systems. Considerable attention is given to the effect of the strong static driving force of the liquid drop (with shell and proximity corrections) potential energy surface on the first and second moments of the observed charge and mass distributions, as well as on associated correlations in the measured two-dimensional probability distribution P(A,Z). Comparison with an appropriate nucleon exchange transport model is made and discrepancies are discussed.