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

The half-life of 241Pu for β decay has been determined on an initially 93 % isotopically enriched material by measuring the decreasing amount ratio n(241Pu)/n(240Pu) 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(240Pu)/n(239Pu) in a 'ratio-of-ratio' measurement which allowed for correction of isotopic effects in the ion source, taking into account the decay of 240Pu(half-life = 6553 a) and 239Pu (half-life = 24 110 a). A regression procedure of the 'ratio-of-ratio' measurements as a function of time resulted in a value for the 241Pu 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. (authors)