Half-life ofPu242from precise low-temperature heat capacity measurements

Heat capacity measurements on three pure compounds, ${\mathrm{PuF}}_3$, ${\mathrm{PuF}}_4$, and ${\mathrm{PuO}}_2$, made from 99.91 at.% ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$, have been used to evaluate the power produced by radioactive decay. The mean specific power was found to be (0.12099 ± 0.00024) mW per gram of plutonium in the samples. The contribution of nuclides other than ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$ to the power was calculated to be (5.15 ± 0.11) μW per gram of plutonium, and so the specific power of pure ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$ is (0.11594 ± 0.00026) ${\mathrm{mWg}}^{-1\mathrm{}}$. A correction for the (5.50 × ${10}^{-4\mathrm{}}$)% spontaneous fission branching reduces the specific power due to α decay to (0.11591 ± 0.00026) ${\mathrm{mWg}}^{-1\mathrm{}}$. Combining this value of the specific power with the total disintegration energy of (4.9823 ± 0.0012) MeV we obtain (3.763 ± 0.009) × ${10}^5$ years as the α half-life of pure ${}_{}{}^{242}{}_{}{}^{}\mathrm{Pu}$.