Fission of highly excited fragments from collisions of 750 A.MeV 
U-ions on
Pb
W. Schwab1,2 - M. Bernas2 - P. Armbruster1 - S. Czajkowski1,3 - Ph. Dessagne4 - C. Donzaud1,2 - H. Geissel1 - A. Heinz1,6 - C. Kozhuharov1 - C. Miehé4 - G. Münzenberg1 - M. Pfützner1,5 - C. Stéphan2 - K. Sümmerer1 - L. Tassan-Got2 - B. Voss1,6
1 Gesellschaft für Schwerionenforschung, Planckstr. 1, D-64291 Darmstadt, Germany
2 Institut de physique nucléaire d'Orsay, IN2P3-CNRS, BP 1, F-91400 Orsay, France
3 Centre d'Etude Nucléaire de Bordeaux-Gradignan, IN2P3-CNRS, BP 120, F-33175 Gradignan, France
4 Institut de Recherches Subatomiques, IN2P3-CNRS BP 28, F-67037 Strasbourg, France
5 Instytut Fizyki Doswiadczalnej, Uniwersytet Warszawski, Hoza 69, PL-00681 Warszawa, Poland
6 Institut für Kernphysik, Technische Universität Darmstadt, Schlossgartenstr. 9, D-64289
Darmstadt, Germany
Received: 26 January 1998 / Revised version: 16 March 1998 Communicated by V. Metag
Abstract
Fragments of relativistic 750 A.MeV U-projectiles were investigated by using
the fragment separator FRS for magnetic selection of reaction products
including ray-tracing and 
E-ToF techniques. For elements between Ge and
Sb, measurements of isotopic yield distributions and velocities revealed three
processes: fragmentation, low-energy fission, and high-energy fission. The last
of these regimes is presently reported. First and second moments of
distributions of mass numbers, atomic numbers and velocities of the
corresponding fragments allowed us to identify 10143Tc56 as the most
probable fragment of a high energy symmetric fission reaction. Moreover, we
could deduce a hypothetical mean fissioning fragmentation product 208Rn
and its highly excited pre-fragmentation parent 227Ra produced in a
primary abrasion reaction at an excitation energy of about 290 MeV.
PACS
25.85.-w Fission reactions -
25.75.-q Relativistic heavy-ion collosions
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