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

In the thermal neutron–induced fission of ²³³U, 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 ⁸⁶Br and ¹³⁶I than usual trend indicate the formation of delayed neutron emitters ⁸⁷Br and ¹³⁷I. 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 ²³³U(n_th,f) reaction were compared with similar data of ^232,235U(n_th,f) and ²³⁸U(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 ²³³U(n_th,f) reaction was also compared with those of ²²⁹Th(n_th,f), ²⁴¹Pu(n_th,f), and ²⁴⁵Cm(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.