Selection of cold transfer and enhanced neutron-pair transfer in the ~(206)Pb + ~(118)Sn reaction

摘要

The neutron transfer in a very heavy asymmetric nuclear system, in ~(206)Pb + ~(118)Sn has been measured using particle-γ coincidence techniques with position-sensitive detectors, 5 EUROBALL-Cluster detectors (EB) and the Heidelberg-Darmstadt NaI-CRYSTAL BALL (CB). The fragments are identified via the known γ-decays of the lowest excited states using the high resolution of EB. Using the unique feature of the set-up with the CB, transfer to well-defined final channels with known quantum numbers is selected using the high-efficiency multiplicity filter of the CB with no second γ-ray, i.e. without feeding. The enhancement in the two-neutron transfer is deduced, for population of the low-lying super-fluid 2~+ states in ~(120)Sn and ~(116)Sn, while the 2n-transition remains in the ground state for the recoiling ~(20X)Pb-nuclei. Large enhancements up to EF approx= 10~3 are observed. This is the first observation of neutron pair-transfer enhancement for a heavy nuclear binary system with superfluid properties with experimentally separated levels.