Post-Neutron Mass Yield Distribution in the Thermal Neutron Induced Fission of U-233

In the thermal neutron-induced fission of U-233, the cumulative and independent yields of various fission products within the mass ranges of 77 to 109 and 123 to 155 have been measured by using an off-line gamma-ray spectrometric technique. The lower yields of Br-86 and I-136 than usual trend indicate the formation of delayed neutron emitters Br-87 and I-137. From the cumulative yields, the post-neutron mass yield distribution was obtained after applying the charge distribution correction. The data from the present and earlier work of our laboratory in the U-233(n(th),f) reaction were compared with similar data of U-232,U-235(n(th),f) and U-238(n,f) reactions to examine the effect of mass difference of the fissioning systems on the fine structure of the mass yield distribution. The mass yield distribution in the U-233(n(th),f) reaction was also compared with those of Th-229(n(th),f), Pu-241(n(th),f), and Cm-245(n(th),f) reactions to examine the effect of charge and mass difference of the fissioning systems and also to examine the different behaviors of standard I and standard II asymmetric modes of fission.