Vol. 53, No. 3
September 1999
pp. 637-646

Fission experiments with secondary beams

J BENLLIURE ^a, S STEINH ÄUSER ^b,C BÖCKSTIEGEL ^b,A GREWE ^b, H-G CLERC ^b ,A HEINZ ^a ,
M E JONG ^b , A R JUNGHANS ^a,J M ¨ ULLER ^b, K-H SCHMIDT ^a and M PF ¨ UTZNER ^c

^a Gesellschaft f¨ ur Schwerionenforschung m. b. H., Planckstrasse 1, 64291 Darmstadt, Germany
^b Institut f¨ ur Kernphysik, Technische Universit¨ at Darmstadt, Schlossgartenstrasse 9, 64289 Darm-stadt, Germany
^c Institute of Experimental Physics, University of Warsaw, Ul Hoza 69, 00-381 Warszawa, Poland

Abstract.

Nuclear fission from excitation energies around 11 MeV was studied at GSI, Darmstadt for 76 neutron-deficient actinides and pre-actinides by use of relativistic secondary beams. The char-acteristics of multimodal fission of nuclei around ²²⁶ Th are systematically investigated and related to the influence of shell effects on the potential-energy and on the level density between saddle point and scission. A systematic view on the large number of elemental yields measured gave rise to a new interpretation of the enhanced production of even elements in nuclear fission and allowed for a new understanding of pair breaking in fission.

Keywords. Nuclear reactions; radioactive beams; nuclear fission; shell effects.

PACS Nos 24.75+i; 25.85.-w; 25.85.Jg; 27.90.+b

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