Abstract: The average particle size for particles distributed in a slurry is determined by transmitting at least one beam of ultrasonic rays of a certain frequency into the slurry, detecting, by separate detector means, on one hand ultrasonic radiation that passes through the slurry and, on the other hand, ultrasonic radiation scattered in the slurry, said detector means forming first and second signals corresponding to the intensities of the passed-through and the scattered radiation respectively, determining the scattering attenuation factor on the basis of said first and second signals and the total attenuation factor by using the intensity of passed-through radiation obtained with pure water, and determining the particle size with the help of the scattering attenuation factor, whereby the radio of said factor and the total attenuation factor is formed in order to eliminate influence of the slurry density.

Abstract: The invention provides an apparatus for measuring the concentrations of elements in a material sample by the capture gamma method, said apparatus including a neutron source in the form of an isotope source or a neutron generator, a moderator surrounding the neutron source and being at least partly constituted by heavy water, a semiconductor detector serving as gamma radiation detector and positioned in the immediate vicinity of the material to be analyzed and in the flux of slow neutrons, so much of the moderator being provided before the detector that this is reached only by a very low number of fast neutrons that have a damaging effect upon the detector. The material itself can form part of the moderator and also graphite is preferably used as a moderator around said heavy water. Furthermore, a body of bismuth having the shape of a cone or a double cone is preferably positioned in front of the neutron source so as to absorb gamma radiation and to scatter fast neutrons.

Abstract: A method and a device for determining or observing the average particle size or particle size distribution in a flow of material, such as a slurry, wherein the material is allowed to flow at a constant velocity through a radiation beam, the time interval distribution of the radiation quanta passing through the material flow is measured, this distribution describing the particle size distribution and offering a possibility to control any changes in the size distribution, and from the measured time interval distribution is subtracted the known time interval distribution of the quanta of the radiation beam emitted by the source of radiation, this known distribution being a Poisson distribution, and, finally, the particle size or size distribution is determined arithmetically on the basis of the observed change in the time interval distribution.