Accumulation of slowing-down neutrons in concrete and reinforced concrete

Results of calculational and experimental investigations into the dose neutron buildup factor Bsub(n) (ratio of the total neutron dose rate to the fast neutron dose rate) in concretes and reinforced concretes of several grades are presented. Experimental Bsub(n) values are obtained form data on the fast neutron energy spectra and the neutron dose rate attenuation function in the materials. Calculational Bsub(n) values are determined using the age theory. The materials with different contents of iron and water have been tested both at room temperature and after heat treatment at 150 deg C, the concrete age exceeding 28 days. The results have shown that the Bsub(n) values are determined by the water content Csub(Hsub(2)0), Bsub(n)(Csub(H)0sub(2)=1.75x12.5 Csub(H0)sup(-1.15)). At Csub(Hsub(2)O)<0.5% the equilibrium neutron spectrum in the materials is not attained and Bsub(n) increases with increasing thickness exponentially