Cold fission of 233U(nth, f)

The recoil spectrometer Lohengrin of the Institute Laue-Langevin in Grenoble was used to measure the yields of light fission fragments separated according to their mass and nuclear charge for the mass-number range 76 ⩽ A L ⩽ 93 in the cold fission regime. Neutron emission being forbidden energetically, the correlated heavy fission fragments including their kinetic energies, as well as the total excitation energy TXE of both fragments were determined by conservation laws. Close to TXE = 0, the yields seem to be strongly influenced by the level density of the fragments. In order to obtain yields for the fission into the ground-states of the two fragments, the measured yields per excitation energy interval were divided by calculated level densities for the two fragment system and extrapolated to TXE = 0. These deduced ground-state yields are influenced by the Q values and by the potential energy of the fragments at the scission configuration. The observed trends in the ground-state yields as a function of nuclear charge and mass may qualitatively be reproduced by calculated penetrabilities through the scission barrier. In these calculations, no correspondence between the calculated penetrabilities and the ground-state yields is found if calculated fragment ground-state deformations are used. There is no difference in the influence of neutron and proton pairing on the ground-state yields.