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

Abstract

Differential cross sections as a function of cm angle were measured for 1n- and 2n-transfer reactions in 238U + 197 Au and197 Au + 197 Au collisions in the energy range from 0.881 Vc to 1.093 Vc and 0.825 Vc to 0.964 Vc, respectively. For 198Au and 199Au from the 238U + 197Au 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 238U + 197Au collisions, and for all transfer products from 197Au + 197Au 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.