Abstract
A method determining 235U/238U isotopic ratio in small uranium samples by neutron activation is described. The sample containing 1-10 μg of uranium is irradiated in a reactor for 20 minutes. After cooling for 24 hours, the sample is dissolved into 25 ml of 1N hydrochloric acid. For the determination of 235U, 10 ml of the solution is taken and 99Mo is separated by means of solvent extraction with α-benzoinoxime. For the determination of 238U, another 10 ml of the solution is taken and 239Np which is formed by 238U (n, γ) 239Uβ→239Np reaction is separated by solvent extraction with thenoyltrifluoroacetone. Both radioactivities are measured with an NaI (T1) scintillation counter, and 235U/238U isotopic ratio is calculated from 99Mo/239Np radioactivity ratio.
Ten analyses of 10.10% 235U samples containing 10 μg of uranium gave a relative standard deviation of 3.9%.
