A new measurement of the half-life of 241Pu using isotope mass spectrometry

The half-life of Pu-241 for beta decay has been determined on an initially 93% isotopically enriched material by measuring the decreasing amount ratio n(Pu-241)/n(Pu-240) as a function of time over more than twenty years. Over the same period the decrease of this ratio was measured relative to the amount ratio n(Pu-240)/n(Pu-239) in a "ratio-of-ratio" measurement which allowed for correction of isotopic effects in the ion source, taking into account the decay of Pu-240 (half-life = 6553 a) and Pu-239 (half-life = 24110 a). A regression procedure of the ratio-of-ratio measurements as a function of time resulted in a value for the Pu-241 half-life of (14.290 +/- 0.006) a (expanded uncertainty with coverage factor k = 2). The slight difference found in the half-life value as measured by the authors on the same material in the period 1976 to 1981 is discussed.