Multi-mode fission on the thermal neutron-induced fission for 233U and 235U

The fission fragment mass yield and energy distribution as a function of fragment mass has been measured precisely on the thermal neutron-induced fission for 233U and 235U. The double-energy measurement has been carried out at the Super Mirror Neutron Guide Facility of the Kyoto University Reactor (KUR). The coincident complementary fragments were measured with two silicon surface barrier detectors which were placed face to face across the target. The measured pulse heights were recorded event by event on a floppy disk with a multi-parameter data acquisition system controlled by a microcomputer. Effective interaction distance between two fragments was derived from the total fragment kinetic energy (TKE) for each fragment mass split. Using the dependency of the effective distance on mass split, TKE was fitted by a superposition of two Gaussian distributions. In this new analysis of TKE distribution, we have observed that the fragment mass distribution consists of two fission modes, namely standard I and II. As results, the standard I fission mode is 7% and II 93% for 235U(nth,f), and the standard I is 4% and II 96% for 233U(nth,f)