Mass Distribution in the Reactor-Neutron-Induced Fission of Thorium-232

The mass distribution in the reactor-neutron-induced fission of ²³²Th has been studied using radiochemical techniques and direct gamma-ray measurements. Absolute fission yields of the standard nuclides ⁹⁹Mo and ¹³²Te were obtained from ²³²Th sources irradiated in a fission counter. The yields of 36 mass chains, including three that have been measured for the first time, were determined both from measurements relative to ²³⁵U(n_th,f) yields and from ²³²Th data alone. The peak-to-valley ratio of the mass-yield curve is found to be ∼100. The light and heavy mass peaks are centered at masses 91 and 140, respectively. The results suggest the presence of a small third peak in the valley of the mass distribution. “Best” yield values are proposed taking into account our values and those from recent compilations.