Fission modes in the reaction Pb-208(O-18,f) - art. no. 014615

Results of fission fragment mass-energy distributions of the compound Th-22 6 nucleus formed in the sub-barrier fusion reaction O-18+Pb-208 at an energ y of O-18 ions E-lab = 78 MeV are reported. The reaction has been studied t wice using two different accelerators, and both sets of experimental data a gree quite well. Performed analysis of the experimental data with the use o f a new multicomponent method has shown that alongside the well-known modes , i.e., the symmetric (S) and two asymmetric modes standard-one and standar d-two, a high-energy mode standard-three has manifested itself. The last na med mode appears due to the influence of the close-to-sphere neutron shell with N approximate to 50 in the light fission fragment group. Theoretical c alculations of the prescission shapes of the fissioning nuclei Th-224,Th-22 6 confirm this conclusion.