(Multi-)nucleon transfer in the reactions 16O, 32S+208Pb

A detailed analysis of the projectile-like fragments detected at backward angles in the reactions 16O,32 S+208Pb at energies below the fusion barrier is presented. Excitation functions corresponding to nucleon transfer with ∆Z = 1 and ∆Z = 2 were extracted, indicating surprisingly large absolute probabilities at subbarrier energies. A comparison of 2p transfer probabilities with time-dependent Hartree-Fock calculations suggests strong pairing correlations between the two protons. Excitation energies in the projectile-like fragments ~15 MeV and ~25 MeV for the 16O and 32S-induced reactions, respectively, indicate the population of highly excited states in the residual nuclei. A comparison with expected optimum Q-values suggests large losses in kinetic energy of the projectile-like fragments. These highly inelastic (large excitation energies) and complex (correlated few-nucleon transfer) processes may be closely related to the depletion of fusion through tunnelling at sub-barrier energies.