Strong enhancement of two-neutron transfer in the system Pb-206+Sn-118

One and two neutron transfer has been measured in the heaviest asymmetric n uclear system with semi magic nuclei showing superfluid properties, in Pb-2 06+Sn-118 collisions at an energy well below the Coulomb barrier with scatt ering orbits covering the largest angles. Particle-gamma coincidence techni ques using 5 Euroball-Cluster detectors (EB) combined in a set-up with the Heidelberg-Darmstadt NaI-Crystal Ball (CB) have been used. Transfer channel s are identified with EB via their known gamma-decays of the lowest excited states. Using the unique feature of the set-up with the CB, transfer to we ll defined final states with known quantum numbers (without feeding) are se lected using the high efficiency multiplicity filter of the CB (no second g amma-ray). The data are analysed using the semiclassical approach and trans fer probabilities are obtained. The enhancement for the two-neutron transfe r populating the low lying superfluid 2(+) state in Sn-120 (and Sn-116), wh ile the Pb-branch is in the groundstate is deduced by comparison with the s trongest single neutron transfer transition. Large enhancements (EF similar or equal to 10(3)) are observed. This is the first direct measurement of e nhancement for a heavy nuclear binary system with experimentally separated levels suggesting a strong contribution from superfluid pair transfer.