München 2006 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 49: Kernphysik/Spektroskopie

HK 49.3: Vortrag

Donnerstag, 23. März 2006, 18:00–18:15, C

Timescale of fission in GeV proton induced reactions — •Frank Goldenbaum¹, Claus-Michael Herbach², Dietrich Hilscher², Ulrich Jahnke², Joel Galin³, Alain Letourneau³, Udo Schroeder⁴, and V.G. Tishchenko² — ¹Forschungszentrum Jülich GmbH D-52428 Jülich — ²Hahn-Meitner-Institut, D-14109 Berlin — ³Ganil, F-14076 Caen — ⁴Univ.Rochester, New York 14627, USA

The excitation energy dependence of fission probability P_f in 2.5 GeV proton induced reactions on Au, Bi, and U has been studied whereby E^* is deduced eventwise form the multiplicity of evaporated light particles. Irrespective of the initial fissility for all three target nuclei at the highest E^* of 1000 MeV P_f amounts to approx. 30%. Intra-nuclear-cascade/statistical model calculations provide a very satisfying reproduction of the observed evolution of P_f(E^*) with E^*. No extra transient delay is introduced showing fission to be decided upon very fast and early in the long deexcitation chain towards scission. The fast decision to fission is supplemented by the observation that a major part (about 80% at E^*=600-900MeV) of all evaporated alpha particles is emitted prior to scission—showing the entire fission process being relatively slow.