SANS studies from porous alumina fibres

The small-angle neutron-scattering pattern from bundles of 3μm diameter porous alumina fibres has been determined and found to be anisometric. Intense scattering at a narrow divergent angle has been observed perpendicular to the fibre axes, coupled with a lower-intensity scattering over all other angles. The pattern has been analysed by means of sector analysis in order to determine the variation of intensity with modulus of the scattering vector over the range 0.006-0.2A-1. A theory has been developed to account for contributions to scattering from, firstly, macroscopic features of the fibres such as alignment distribution and lack of straightness and, secondly, from internal porosity allowing for distributions of size and of orientation with respect to the fibre axis. The parameters of the size distributions have been estimated from the two-dimensional data by directly fitting the scattering equations using a weighted non-negative least-squares principle. (orig.)