Fission lifetimes of Th nuclei measured by crystal blockingS.A. Karamian1, J.S. Forster2, J.U. Andersen3, W. Assmann4, C. Broude5, J. Chevallier3, J.S. Geiger2, F. Grüner4, V.A. Khodyrev6, F. Malaguti7 and A. Uguzzoni7
1 FLNR JINR, 141980 Dubna, Russian Federation
2 Départment de Physique, Université de Montréal, Montréal, Quebec, H3C 3J7 Canada
3 Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C, Denmark
4 Sektion Physik, Universität München, 85748 Garching, Germany
5 Physics Department Weizmann Institute of Science, Rehovot, Israel
6 Moscow State University, Moscow, Russian Federation
7 Department of Physics, University of Bologna and INFN Bologna, Italy
(Received: 2 October 2002 / Revised version: 1 January 2003 / Published online: 29 April 2003)
Crystal blocking lifetime measurements have been made for highly excited Th nuclei with neutron number well removed from the stability line. Thin W crystals were bombarded with 32S ions in the energy range 170-180 MeV and the yield of fission fragments was measured for emission close to a axis. The fission blocking dips are compared to the appropriately scaled ones for elastic scattering of the 32S beam ions and no significant difference is seen between the dips. This implies that the fraction of nuclei fissioning with lifetimes longer than 10 as is less than 2%. Fission lifetimes are increased by viscosity in the nuclear mass flow and comparison with a statistical model calculation indicates that the viscosity parameter, , must be lower than for Th and U nuclei near -stability. The effect of the N = 126 magic number is discussed.
24.75.+i - General properties of fission.
61.85.+p - Channeling phenomena (blocking, energy loss, etc.).
© Società Italiana di Fisica, Springer-Verlag 2003