Particle sizing with a laser transmittance photometer and the Mie theory

A new method is proposed for nondestructively sizing particles in suspension with a special transmittance photometer. Its axial photocell has a controllable acceptance angle, γ. Extinction,
E(\gamma) = \log_{10}
transmittance
^-1
of a suspension is measured with several γ-values. The results are used to calculate the ratio
E(\gamma)/E(0)
, the fraction of the total light scattered at angles larger than γ. For three γ-values, this ratio is interpreted in terms of particle size with the Mie equations for scattering or the equivalent. Tests with calibrated latex spheres (diameter
0.2-6.0 \mu
m) indicate the method to be reasonably accurate. Its advantages are convenience, simplicity of the apparatus and procedure, and the fact that it can nondestructively monitor ongoing processes which alter structure, i.e., in live biological cells or large components thereof.