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Zeitschrift für Physik A Atomic Nuclei

, Volume 326, Issue 3, pp 313–326 | Cite as

Evidence for quasi-fission in40Ar+208Pb collisions near the coulomb-barrier

  • H. Keller
  • K. Lützenkirchen
  • J. V. Kratz
  • G. Wirth
  • W. Brüchle
  • K. Sümmerer
Article

Abstract

Fission-fragment angular distributions were measured in the reaction of40Ar with208Pb near the fusion barrier. For nearly symmetric mass-/charge splits we find angular distributions symmetric around θ=90 degrees, however, with unusually large anisotropies. These develop gradually into forward-backward asymmetric distributions as one moves away from mass-/charge symmetry. This indicates that non-compound fission (‘quasi-fission’) competes with true fusion-fission. The relative contribution of quasi-fission to the total fission cross section is somewhere between 51 and 85%. In the framework of the extra-push model this is equivalent to an extra-extra push energy for compound-nucleus formation inside the true fission saddle point of 4<E xx <9 MeV in agreement with a recent empirical parametrization of fusion-barrier shifts based on fusion-fission cross sections. On the basis of cross sections for fusion-evaporation residues it had previously been concluded that fusion of40Ar with Pb isotopes occurs unhindered. Possible reasons for this apparent discrepancy are discussed.

PACS

25.70.Jj 

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Copyright information

© Springer-Verlag 1987

Authors and Affiliations

  • H. Keller
    • 1
  • K. Lützenkirchen
    • 1
  • J. V. Kratz
    • 1
  • G. Wirth
    • 2
  • W. Brüchle
    • 2
  • K. Sümmerer
    • 2
  1. 1.Institut für KernchemieUniversität MainzMainzFederal Republic of Germany
  2. 2.Gesellschaft für Schwerionenforschung mbHDarmstadt 11Federal Republic of Germany

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