Measurement of the average energy and multiplicity of prompt-fission neutrons from ²³⁸U(n,f) and ²³⁷Np(n,f) from 1 to 200 MeV

Abstract

Abstract. Taking advantage of the neutron source of the LANCSE, it has been possible to obtain a measure of the velocity distribution and the number of prompt-neutrons emitted in the neutron-induced fission of 238 U and 237 Np over a broad incident neutron energy range. The mean kinetic energy was extracted and is shown as a function of the incident-neutron energy. We confirm here the observation, for both reactions, of a dip around the second-chance fission which is explained by the lower kinetic energy of the pre-fission neutrons. Such a observation is reproduced by Los Alamos model as implemented at Bruyères-le-Châtel and by the Maslov model. As far as the neutron multiplicity is concerned, a similar dip is observed.

Templates of expected measurement uncertainties for average prompt and total fission neutron multiplicities

“…Mainly one ratio-type measurement was encountered in EXFOR entries for 239 Pu ν p and ν t [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][34][35][36][37][38][39][40][41][42], namely, ratio liquid-scintillator measurements, which will be discussed below. Some ν p data have also been measured with setups that are traditionally used to determine prompt fission neutron spectra (PFNS), see e.g., [51][52][53][54]. To this end, the PFNS is measured via the techniques described in reference [55], extrapolated to span the entire outgoing-neutron energy, E out , range, and then integrated over these energies to yield ν p .…”