Abstract: The invention provides a method and apparatus for determining particle size distribution of particulate samples. Particle size distribution is determined by measuring particle concentration (based on radiation transmittance measurement) as a function as time, and position along the direction in which the particles are settling. Preferably, the particles in a suspension are subjected to a centrifugal force field by rotation in a disc-shaped settling tank. A radiation source and detector scanning assembly, which is capable of radial movement with respect to the rotating settling tank, measures transmittance through the sample as a function of time and radial position. Also provided are mathematical relations suitable for determining particle size distribution from the measured data.