Fast-Neutron Spectrum and Dose-Rate Measurements in Water and Aluminum-Water Laminations

The fast-neutron spectrum and dose rate were measured at various distances from a point fission-neutron source in water and in two aluminum and water mixtures using seven threshold reaction detectors and p-i-n silicon diode dosimeters. The experimental results were compared with calculations made using the ANISN computer code. The threshold reactions used were the ¹¹⁵In(n, n′), ³²S(n, þ), ⁶⁴Zn(n, þ), ²⁷Al(n, þ), ^56Fe(n, þ), ²⁴Mg(n, þ), and ²⁷Al(n, α). Using 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 well with the results predicted by the ANISN code. The fast-neutron dose rate was measured directly using p-i-n junction 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