LIFETIME OF EXCITED U-234,U-235 NUCLEI PRODUCED IN THE REACTION TH-232(ALPHA, XNF)

The blocking technique is used to measure the Lifetimes of excited U-2 34,U-235 nuclei produced in the reaction Th-232(alpha, xnf). The energ y of bombarding a particles was varied between 20.0 and 31.2 MeV. The resulting experimental data are analyzed in the statistical theory of nuclear reactions with allowance for the lifetimes of the excited stat es of the first and second potential wells. This makes it possible to determine the absolute values of the level density in the second poten tial well and the depth of the second minimum of the U-234 fission bar rier. It is shown that these absolute values of the level density can be described in a phenomenological model only under the assumption tha t the axial and mirror symmetries of nuclei are violated in the states of the second well.