Particle sizing by forward lobe scattered intensity-ratio technique: errors introduced by applying diffraction theory in the Mie regime.

Hodkinson proposed that Fraunhofer diffraction theory could be used as an approximation to Mie theory in particle size measurement by a forward lobe scattering intensity ratio technique. This paper describes a technique for quantifying theoretical errors involved in this approximation. Theoretical errors are computed for monodisperse latex spheres in air and in water at angle pairs of 5 degrees /2.5 degrees , and 10 degrees /5 degrees , and 20 degrees /10 degrees . Errors oscillate with particle size in a manner related to oscillations in particle extinction coefficient and are generally within +/-40%. These are somewhat greater than suggested previously. Oscillations are stronger and errors generally larger in air than in water.