The half-life of ${}_{}{}^{240}{}_{}{}^{}\mathrm{Pu}$ was measured by $\alpha$ counting with an intermediate geometry proportional counter, using oxidation-reduction titration of the plutonium to measure its mass. The specific activity is (5.033 ± 0.004) × ${10}^{11}$ $\alpha$ disintegrations per minute per gram; the half-life is 6569 ± 6 yr (one standard deviation error).

RADIO ACTIVITY ${}_{}{}^{240}{}_{}{}^{}\mathrm{Pu}$ half-life, specific activity; measured: $\alpha$ activity by intermediate geometry $\alpha$ counter; plutonium concentration, redox titration.

• Received 17 March 1978

DOI:https://doi.org/10.1103/PhysRevC.18.969