Double-Energy Single-Time-of-Flight Measurements of Fission Fragments in Thermal-Neutron-Induced Fission ofU235

An experiment has been performed on the thermal-neutron-induced fission of ${\mathrm{U}}^{235}$, in which the energies of complementary fission fragments and the time of flight of one fragment were measured. Fragment masses after neutron emission were obtained directly from this information. Pre-neutron masses and kinetic energies were deduced by means of a reflection method which simulates a double-time-of-flight experiment. Subtraction of post-neutron from primary fragment masses then gave the number of neutrons emitted by single fragments in each event. Among the results presented are the distributions of the numbers of neutrons emitted by single fragments of fixed mass. This information is very difficult to obtain from other types of experiments, and there has been no previous publication of such results for any fissioning nucleus. The results also include the average number of neutrons emitted as a function of mass and total kinetic energy, as well as mass distributions in fixed kinetic energy intervals, and total kinetic energy distributions at fixed fragment masses.