Half-life of 239Pu by two independent methods

The 239Pu half-life was measured both by α counting with an intermediate geometry proportional counter and by mass spectrometric measurements of the rate of 235U formation, using isotopic dilution with titrated 233U and 238U spikes. The plutonium concentration was measured by oxidation-reduction titration, using NBS-certified plutonium as a reference standard. The results from the two measurements were statistically consistent and their average gives for the 239Pu half-life the value 24131 +- 16 yr, corresponding to a specific activity of (1.3758 +- 0.0009) x 1011 dis/min per gram 239Pu (one standard deviation error). This result agrees with some recent measurements, but is in marked disagreement with a number of earlier ones