ν(m*) MEASUREMENTS FOR 233U AND 235U(nth,f)Research Reactor Institute, Kyoto University Kumatori-cho, Sennan-gun, Osaka 590-04 Japan I. Kanno Japan Atomic Energy Research Institute Tokai-mura, Naka-gun, Ibaraki 319-11 Japan I. Kimura Department of Nuclear Engineering, Kyoto University Yoshidahonmachi, Sakyo-ku, Kyoto 606 Japan Number of prompt neutrons as a function of individual fragment mass ν(m*) was measured for the thermal neutron-induced fission of 233U and 235U. By measuring the velocities and energies of two fission fragments simultaneously, preneutron-emission fragment mass m* and postneutron-emission fragment mass m were obtained. ν(m*) was deduced by subtracing m from m*. The fragment velocity was measured by a time-of-flight (TOF) method, and the start time was detected by a very thin plastic scintillator film detector. A silicon surface barrier detector was used to measure the fragment energy, which was also used as a stop detector of the TOF. The result of ν(m*) for 233U(n,f) was in agreement with other data in the heavy fragment region but was 20 to 50% larger than those in the light one. ν(m*) for 235U(n,f) showed a factor of 1.5 to 2 larger in the light fragment region and smaller in the heavy one than the other data. KEYWORDS: 233U, 235U, thermal neutron, fission, number of prompt neutrons, fragment mass, velocity, kinetic energy, thin film detector |