The rate of energy production by alpha-disintegration of plutonium (239) has been measured calorimetrically. The method was to measure the rate of evaporation of liquid nitrogen by a 120-gram sphere of metallic ${\mathrm{Pu}}^{239}$ and compare this rate with that produced by the introduction of electrical energy. The power produced by ${\mathrm{Pu}}^{239}$ is 1.923±0.019 abs. watts·${\mathrm{gram}}^{-1\mathrm{}}$. Combining this with the energy per alpha-particle determined from range and range-energy measurements, one obtains 2.411×${10}^4$ years as the half-life of ${\mathrm{Pu}}^{239}$ with respect to alpha emission.

• Received 6 January 1947

DOI:https://doi.org/10.1103/PhysRev.71.582