Measurement of prompt neutron number for thermal neutron induced fission of 239Pu

Neutron multiplicity as a function of fragment mass v-bar(m*) was measured for the thermal neutron induced fission of 239Pu. By measuring the velocities and energies of two fission fragments simultaneously (2V2Emeasurement), both of the pre-neutron emission fragment mass m* and the post-neutron mass m were obtained. Fragment mass dependent neutron multiplicity was deduced by subtracting m from m*. The fragment velocity was measured by a time-of-flight (TOF) method, for which the start signal was triggered by a very thin plastic scintillation film detector (TFD) and the stop signal was obtained by a silicon surface barrier detector (SSBD) which was also used for the measurement of the fragment kinetic energy. The obtained distribution of v-bar(m*) agreed well with that of Apalin et al's. (author)