Use of Nuclear Plates for the Determination of the Uranium and Thorium Contents of Radioactive Ores

Abstract

MR. D. H. PIERSON¹ has recently described a very ingenious method of determining the thorium–uranium ratio in radioactive ores. The main objection to his method is that it requires rather elaborate electronic equipment, and certainly could not be used in the field. In this respect the nuclear plate method presents great attractions, since the only essentials are some form of dark room and a fairly good microscope provided with a good micrometer eyepiece. A thick layer of the ore can be used, so that the ore need only be moderately finely powdered in a mortar and screened through a suitable mesh before the plate is placed in contact with it. We have found that an exposure time of eight minutes is suitable for thorium oxide, when in radioactive equilibrium. This exposure gives about twenty tracks in the field of a microscope using a 4-mm. dry objective and a × 10 eyepiece. Thus, even for comparatively poor ores, the exposure required would not be unduly long.