Proton Recoil Measurements of the ²⁵²Cf Fission Neutron Leakage Spectrum from an Iron Sphere

Proton recoil measurements of the ²⁵²Cf fission neutron leakage spectrum from a 50-cm-diam iron sphere are performed as a means of checking the degree to which the ENDF/B-VI iron inelastic scattering cross section resolves the well-known discrepancy between predicted and observed neutron transport. These measurements were performed at the National Institute of Standards and Technology using a rotating proton-recoil spectrometer over an energy range of 50 keV to 4.5 MeV. In addition, Monte Carlo neutron transport calculations were performed of the iron-moderated neutron spectrum generated in the experiment. Below 1 MeV, the spectral measurements are in good agreement with a corresponding calculation for the iron-moderated neutron leakage spectrum obtained using the ENDF/B-VI cross-section library. However, the calculation continues to underpredict the neutron fluence above 1 MeV by as much as 11%, which is greater than the average statistical uncertainty of the measured data. Finally, the measurements are compared with those obtained from a similar set of experiments made by two different laboratories in the Czech Republic. The results compare favorably with both of these measurements and indicate the best agreement with the Monte Carlo transport calculations with respect to the integral neutron fluence.