Monitoring shale in iron ore

Apparatus for determining the concentration of a radioactive constituent in a sample of material comprises: a) a radiation detector adapted to monitor the characteristic gamma radiation of the constituent; b) a weightometer adapted to measure the mass of material in the sample; and c) electronic means to calculate the ratio of the intensity of the characteristic radiation monitored by the detector to the mass of the sample measured by the weightometer. The weightometer is a gamma radiation adsorption weightometer having as its source of gamma radiation the isotope barium-133. A gamma radiation detector with at least two energy windows is used as the detector of the characteristic gamma radiation and, independently, of gamma radiation of the energy emitted by the barium-133. In a second claim material is carried on a conveyor. There is a sorting means, responsive to the output of the electronic calculating means, for controlling the destination of the sample on leaving the conveyor