Quasielastic transfer reactions in 238 U + 197 Au and 197 Au + 197 Au collisions near the Coulomb barrier

Differential cross sections as a function of cm angle were measured for 1n- and 2n-transfer reactions in 238 U + 197 Au and 197 Au + 197 Au collisions in the energy range from 0.881 V c to 1.093 V c and 0.825 V c to 0.964 V c , respectively. For 198 Au and 199 Au from the 238 U + 197 Au collisions, for reduced distances of closest approach d o 1.55 fm, the angular distributions at all bombarding energies are well described by the semiclassical theory. Equivalently, the transfer probabilities show the expected exponential decrease with increasing d o over many orders of magnitude. For all other transfer products from 238 U + 197 Au collisions, and for all transfer products from 197 Au + 197 Au collisions, markedly reduced cross sections relative to the semiclassical theory are observed for central collisions at all bombarding energies, even for values of d o that are well outside the region where absorption is known to set in. Only for the more peripheral collisions, one observes agreement of the angular distributions (transfer probabilities) with the semiclassical expectations. The deviations for central collisions are absent for reactions with positive Q gg values and scale roughly with increasingly negative values of Q gg , i.e. with increasing Q -value mismatch. Channel coupling is proposed as the relevant mechanism.