Investigation of the biological shielding properties of ferruginous and sandy clays

The biological shielding properties of two local clays, the ferruginous clay from Nsaba and the sandy clay from Winneba, at three different firing temperatures (9500C, 10000C and 11000C) have been investigated. The attenuation coefficient and hence the half-value-layers for different gamma energies determined revealed that Portland concrete is better than the clays for lower gamma energies but the reverse is true for high energy gammas. The diffusion lengths of thermal neutrons in the clays were observed to be relatively shorter than the 6.61 cm recorded for Portland concrete. The worst value obtained being 1.81 cm. There is the possibility of improving on the shielding properties of the clays by adding boron or cadmium and firing below 444.60C in the former and 746.40C in the latter or by hand pressing during moulding to reduce the porosity. The values of the moduli of rupture indicates their general weakness in comparison with concrete but again it is believed that hand pressed bricks would be stronger. (author)