Evaluation of ²⁵²Cf Prompt Fission Neutron Data from 0 to 20 MeV by Watt Spectrum Fit

Recent measurements define the prompt fission neutron spectrum of ²⁵²Cf from 25 keV to 20 MeV with sufficient accuracy to show that the standard representation by a Maxwell spectrum with the temperature parameter T_M = 1.42 MeV is not adequate. The next simplest macroscopic representation, a Watt spectrum with the two parameters T_w = 1.18 MeV and E_w = 0.36 MeV, fits the recent data surprisingly well, at least as well as the best currently available microscopic models of fission neutron emission. The resulting chi-square does not indicate any need for a more sophisticated description, nor is the fit improved by refinements such as superposition of two Watt distributions (for a representative fragment pair), or relativistic corrections.