Neutron Spectrum Measurement in a Fast Critical Assembly

A measurement of the neutron spectrum at the center of a large, dilute fast reactor is reported over the energy interval from 1 keV to 1 MeV. Resolution of the measurement was about 20% (FWHM) except at the lower energies. Errors in the measurement are described and a comparison made of the measured result with a multienergy-group calculation. There exists fair agreement between the measured spectrum and the multigroup calculation.