Determination of low levels of uranium impurity by fission track registration using mica and polycarbonate detectors

Abstract

A first attempt to determine low levels of uranium by fission track registration was made by optical counting over wide fields in mica and polycarbonate detectors under high magnification. Homogeneous distribution of fission tracks was achieved by registrations using liquid ampoules and powder pellets. Extremely low uranium concentration in twofold distilled water was determined to be 0.039 ± 0.002 ppb (i.e. ng g-1). Low levels of uranium in solids were well determined by mica and Lexan detectors, viz., 1.42 ± 0.27 ppm (μg g-1) in a photoelectric semiconductor; 0.11 ± 0.03 ppm and 0.06 ± 0.02 ppm in different types of toothpaste. The background uranium content of track detectors and binding material were primarily estimated to be 1.18 ± 0.01 ppb in annealed muscovites (Brazilian Clear Ruby Mica), 1.02 ± 0.23 ppb in Lexan polycarbonate, and 2.20 ± 0.93 ppb in methyl cellulose. Repeated results of uranium determination by duplicate detection, using mica and Lexan on identical samples irradiated at different neutron fluences, were seen to be very consistent. These homogenized track registration techniques can be applied reliably to the determination of low concentrations of uranium impurity, between 10-2 ppb and 10 ppm.