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

Abstract

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.