Measurement and Analysis of Neutron Spectra in a Fast Subcritical Assembly Containing Uranium-235, Uranium-238, and Beryllium Oxide

Neutron spectra have been measured between 50 eV and 8 MeV by the time-of-flight method in the core of a fast subcritical assembly, designated STSF-1A. This core is loaded with plate-type elements consisting of BeO, enriched uranium, and depleted uranium. The measurements were made at the surface of the central BeO plate. Reduction of the data and comparison to transport calculations followed the procedures used for the STSF-2 and STSF-2A assemblies, which were described in detail in a previous paper. The STSF-1A is similar in most significant details to ZPR-3 Assembly 57, built at ANL/Idaho, in which the spectrum was measured with a proton recoil detector, and this similarity permitted a comparison of the time-of-flight and proton-recoil techniques. The two methods have been found to be generally in satisfactory agreement.