MEASURED AND PREDICTED VARIATIONS IN FAST NEUTRON SPECTRUM IN MASSIVE SHIELDS OF WATER AND CONCRETE

摘要: Abstract The absolute magnitude, and the variations in form, of fast neutron spectrum during deep penetration (0.8 – 1.1 m) massive shields water, ordinary magnetite concrete have been studied by using threshold detectors (In(n, n′), S(n, p), Al(n, α)). results compared with predictions two rigorous (NIOBE, Moments method) non-rigorous (multigroup removal-diffusion) shielding codes (NRN, RASH D). predicted were general within 50% measured ones, ie. showed as good or better accuracy than thermal epithermal flux same small-reactor configurations. No difference was found between methods. changes relative form (indicated (Al/S) (In/S) reaction rate ratios amounting to factors up 3–4 a one metre water) rather accurately (within 10–30%) all photonuclear excitation 335 keV level used for detecting In(n, n′) distort completely In water at penetrations > 50 cm.