CSIRO Minerals has developed a particle size analyser based on ultrasonic attenuation and velocity spectrometry combined with gamma-ray transmission. The analyser now incorporates a gamma-ray transmission gauge utilising an ultra-low activity radioisotope source that is exempt from licensing regulations. The particle size analyser is applicable to the measurement of 0.1-1000 mum diameter particles directly in highly concentrated slurries without dilution. The technique has been optimised for use in mineral processing slurries such as those found in grinding, circuits. These slurries often have high solids loadings, broad particle size distributions, and multiple components of the solid phase. The technique is particularly useful for applications where excess fines may be present. The analyser has been extensively tested on a range of industrial slurries and has been demonstrated in a number of laboratory and plant trials on iron ore, silver/lead/zinc ore and titanium dioxide pigment slurries. CSIRO is currently developing particle size analysis systems for permanent installation in two mineral plants in late 2001 or early 2002. (C) 22002 Elsevier Science Ltd. All rights reserved.