Determination of porosity in anisotropic fractal systems by neutron scattering:

Small-angle scattering from two-phase isotropic systems requires the scattering to be invariant to determine the relative fractions of each phase in the material. For anisotropic systems the measurement yields a result that depends on the projection of the phases onto the scattering plane, normal to the incident radiation. When the scattering system has a unique axis such that there is no preferred direction in the plane normal to that axis, the scattering gives elliptical contours on the two-dimensional detector. Two different measurements of projected phases, one with the incident beam direction coincident with the unique axis and the other normal to that axis, can be combined to give a threedimensional description of the system and therefore lead to a determination of the total porosity of the system.