Half-life ofPu242

The half-life of ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$ was measured relative to the half-lives of ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$ and ${}_{}{}^{238}{}_{}{}^{}\mathrm{Pu}$ in two independent sets of experiments. Synthetic mixtures were prepared using enriched isotopes of ${}_{}{}^{238}{}_{}{}^{}\mathrm{Pu}$, ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$, and ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$. The $\alpha$ activity ratios in these mixtures were determined by $\alpha$ spectrometry on electrodeposited sources using a silicon surface barrier detector while the atom ratios were obtained by mass spectrometry. The $\alpha$ activity ratios and the atom ratios were so chosen that these could be measured with a high precision and accuracy. A half-life value of (3.742±0.024) × ${10}^5$ yr is obtained using the half-life of ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$ as 24110 yr. The value obtained using the half-life of ${}_{}{}^{238}{}_{}{}^{}\mathrm{Pu}$ as 87.74 yr is (3.766±0.025) × ${10}^5$ yr. The average of these two independent sets of experiments leads to a half-life value of ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$ as (3.754±0.025) × ${10}^5$ yr. The uncertainty given on the values is a combination of the one standard deviation on the average value and the error evaluated from estimates on various error components. The discrepancy existing in the earlier published values for the half-life of ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$ determined relative to the half-lives of ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$ and ${}_{}{}^{238}{}_{}{}^{}\mathrm{Pu}$ is resolved.