Determination of uranium equilibrium in rocks using α and fission fragment radiography

Abstract

A technique has been developed that permits the determination of uranium-daughter product equilibrium in polished sections by combining α and fission fragment radiography. The procedure consists of placing an uncovered rock section in contact with, first, an α-sensitive emulsion to record the α-particle emission from uranium and its eight α-emitting daughter products, and second, an emulsion sensitive to fission fragments (but not α-particles) to record the tracks of fission fragments produced from U 236 when the slide is bombarded with thermal neutrons. A sample with approximately 100 p.p.m. of uranium in equilibrium emits about 570 α-tracks/cm 2 per day in an autoradiograph, and about 10,000 fission fragment tracks/cm 2 per hr, when exposed to a neutron flux of 2·25 × 10 10 neutrons/cm 2 per sec. A sample deficient in uranium daughter products will release relatively more fission fragment tracks than α-tracks, and the opposite is true if the sample has a deficiency of uranium with respect to daughter products. The technique has the advantages of being non-destructive, applicable on a micro scale, and suitable for use on samples having uranium contents as low as 10 p.p.m.