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Enhanced neutron pair transfer and collective excitations in the system 206Pb + 118Sn at barrier energies

  • I. Peter
  • W. von Oertzen
  • S. Thummerer
  • H.G. Bohlen
  • B. Gebauer
  • J. Gerl
  • M. Kaspar
  • I. Kozhoukharov
  • T. Kröll
  • M. Rejmund
  • H.J. Wollersheim
  • I.J. Thompson

Abstract:

At energies below the Coulomb barrier, neutron transfer and Coulomb excitation have been measured in a very heavy asymmetric nuclear system, in 206Pb + 118Sn. These are semi-magic nuclei showing super-fluid properties. Particle-γ coincidence techniques using 5 Euroball Cluster detectors (EB), combined in a set-up with the Heidelberg-Darmstadt NaI Crystal Ball (CB), have been used. Position-sensitive detectors allowed the observation of scattering processes covering angles from 110 up to 150 degrees. 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 data are analysed using the semi-classical approach and transfer probabilities are obtained. Coulomb excitation has been analysed using known transition probabilities. The enhancement is deduced for the two-neutron transfer populating the low-lying super-fluid 2+ states in 120Sn and 116Sn, while the 2n transition remains in the ground state for the 20NPb nuclei. Large enhancements up to EF ≃ 103 are observed. This is the first observation of neutron pair transfer enhancement for a heavy nuclear binary system with super-fluid properties with experimentally separated levels. The calculations with microscopic 2-neutron wave functions, with configuration mixing over six shell model configurations and using the coupled reaction channels approach, reproduce well the observed probabilities and the enhancement.

PACS. 24.10.Eq Coupled-channel and distorted-wave models – 25.70.Hi Transfer reactions 

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Copyright information

© Società Italiana di Fisica and Springer-Verlag 2003

Authors and Affiliations

  • I. Peter
    • 1
  • W. von Oertzen
    • 2
  • S. Thummerer
    • 2
  • H.G. Bohlen
    • 2
  • B. Gebauer
    • 2
  • J. Gerl
    • 1
  • M. Kaspar
    • 1
  • I. Kozhoukharov
    • 1
  • T. Kröll
    • 3
  • M. Rejmund
    • 1
  • H.J. Wollersheim
    • 1
  • I.J. Thompson
    • 4
  1. 1.Gesellschaft für Schwerionenforschung Darmstadt, Planckstraße 1, 64291 Darmstadt, GermanyDE
  2. 2.Hahn-Meitner-Institut Berlin, Glienicker Straße 100, 14109 Berlin, GermanyDE
  3. 3.INFN, Sezione di Padova,Via Marzolo 8, 35131 Padova, ItalyIT
  4. 4.Department of Physics, University of Surrey, Guildford GU2 7XH, UKGB

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