Half-Lives ofPu240andPu239

The half-lives of ${\mathrm{Pu}}^{240}$ and ${\mathrm{Pu}}^{239}$ have been determined by measuring the specific alpha activity and the ${\mathrm{Pu}}^{240}$ content of four plutonium samples which had received different amounts of neutron irradiation. With the assumption that ${\mathrm{Pu}}^{238}$ contributes 13 percent to the observed increase in alpha activity, the half-life of ${\mathrm{Pu}}^{240}$ is 6300±600 years. The half-life of ${\mathrm{Pu}}^{239}$ is found to be 24 400±500 years.