Neutron Energy Spectrum Measurements in Unmoderated Assemblies

The neutron energy spectrum at the center of the dilute fast core of the coupled fast-thermal reactor, ZPR-V has been studied by use of fission chambers having electrodes quantitatively electrodeposited with U²³⁴, U²³⁵, U²³⁶, and U²³⁸. Atomic fission ratios found with these four uranium isotopes determine a four-group neutron energy spectrum which can readily be measured as a function of position in the core by use of suitable drive units. The same fission chamber procedure has been used to study the equilibrium neutron energy spectrum in a natural uranium exponential column at Los Alamos. The results of measurements in these two spectra are shown and compared with theoretical predictions. The ZPR-V results are also compared to an analysis of this spectrum made by use of nuclear emulsions for the range 0.2 to 2.2 mev.