Determination of porosity variations in powder beds

A gamma-ray attenuation technique for detecting local porosity variations in packings of pharmaceutical powders has been developed and assessed. It proved necessary to employ an empirical expression describing the attenuation coefficient of the model material, lactose, as a function of porosity. The precision of measurement of local porosity can be pre-selected due to the statistical basis of the method, and local porosity measurements with 95% confidence intervals of +/- 0.005 can readily be carried out. A method of producing grey-scale images of porosity distributions has been employed to enable the degree of inhomogeneity of a powder bed to be seen.