New determination of theU233specific activity and half-life

A new determination of the ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$ specific activity has been made using a method developed for measuring the longer-lived uranium isotopes. Samples prepared by molecular plating were counted in an intermediate-geometry $\alpha$ proportional counter with a flat pulse-height plateau. For each sample, the small amount of residual non-plated uranium was evaluated by counting in a $2\pi$ counter. Energy analysis with a silicon-junction detector allowed accurate measurement of the small amount of activity not ascribable to ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$ and ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$. The ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$ activity was corrected for by calculation from the mass-spectroscopically-measured isotopic concentration. The specific activity was measured as 21 405 ± 20-dis/min μg ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$, corresponding to a half-life of (1.5911 ± 0.0015) × ${10}^5$ yr. The quoted error is statistical (standard error of the mean), based upon observed scatter of the data.