Measurement Of Fast Neutron Spectrum In The Tr O Heavy Water Critical Facility

The fast neutron spectrum of the Coupled Fast Reactivity Measurements Facility (CFRMF) at the Idaho National Engineering Laboratory (INEL) is being used to study and standardize fast reactor neutron dosimetry materials and methods. The CFRMF has been designated a ''benchmark experiment'' to test the cross section data of dosimetry materials as well as other materials used and produced in fast reactors. Information about the neutron energy spectrum of the CFRMF is presented. (auth).

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The fast neutron spectrum was measured by seven threshold reaction detectors at various distances from a point fission neutron source in water and in two aluminum and water mixtures. The attenuation of the fast neutron dose rate and of the thermal neutron flux was also determined. The experimental results were compared with calculations made with the ANISN computer code. By use of experimentally determined counting efficiencies, absolute saturation activities of the threshold reaction products were determined. A method of neutron spectrum unfolding was devised which represented the fast neutron spectrum by a group of successive exponentials calculated from the saturation activities. The reported spectra generally agreed with the results predicted by the ANISN code. The fast neutron dose rate was measured directly with p-i-n silicon diode dosimeters and indirectly by applying flux-to-dose conversion factors to the measured fast neutron flux. Good agreement was obtained between these measurements and calculations. The saturation activities from the 32S(n, p) reaction were compared with the measured and calculated dose rates and an activity-to-dose-rate conversion factor was estimated. (Author).