Blocking technique measurements of the induced fission time of U nuclei

The blocking technique was used to measure lifetimes of the excited U-234,U -235 nuclei produced in the Th-232 + alpha reaction at the energy of bombar ding alpha-particles in the range 20.0-31.2 MeV. The resulting experimental data are analyzed in the statistical theory of nuclear reactions with allo wance for the lifetimes of the excited states of the first and second poten tial wells of the double-humped fission barrier. The absolute values of the level densities in the second potential well, fission barrier parameters a nd type of shape symmetry in the second well were determined. (C) 2000 Else vier Science B.V. All rights reserved.