Quasi-elastic neutron transfer and pairing effects in the interaction of heavy nuclei

Experimental results for neutron transfer in the system 112Sn+120Sn are presented for three incident energies 4.25, 4.55 and 4.8 MeV/u. Final states are not resolved, however, the data represent transitions between low-lying states. The data are used to extract transfer probabilities and formfactors for neutron transfer between low-lying states. A DWBA analysis gives a quantitative description of the observed overall cross section for one-neutron transfer. The enhancement of the two neutron transfer is discussed using semiclassical arguments; in this context additional data for the systems 86Kr+208Pb, 58Ni+208Pb, 136Xe+238U and 208Pb+238U are discussed. The general features of quasielastic transfer probabilities defined in a macroscopic way by an energy resolution of ca. 5-10 MeV, which is so far the only experimental possibility, are shown to give meaningful information on single nucleon and pair transfer between heavy nuclei. The latter point is also supported by coupled channel calculations for the transfer flux in these reactions and it is shown that a strong coupling situation is only reached at distances, where very strong absorption due to deeply inelastic reactions has set in. (orig.)