A new evaluation of the half-life of ²⁴¹Pu

A new evaluation of the half-life of ²⁴¹Pu has been made by combining previous results from earlier methods and techniques with further measurements of the isotopic ratio of an initially enriched ²⁴¹Pu material. A correction to the previous published value has had to be made. The half-life of ²⁴¹Pu is an important parameter for the measurement and control of amounts of plutonium as the decay of this isotope is usually the largest contributor to the uncertainty of estimations of the amount of total plutonium after storage. The value of the half-life together with its associated uncertainty needs to be known with a high degree of confidence. However, the half-life value of ca. 14.3 a (years) means the decay of the isotope is difficult to measure over one or more half-lives using a single method or instrument. The method employed in this evaluation is designed to conform to the Guide to the Expression of Uncertainty in Measurements (GUM) (International Organisation for Standardisation, Guide to the Expression of Uncertainty in Measurement, ©ISO, ISBN 92-67-10188-9, Geneva, Switzerland, 1993)¹ and care was taken to ensure that all measured values over the 30 year measurement time-span have been included. The value recommended from this set of measurements is 14.325 a ± 0.024 a (k = 2). This agrees with the value from the first measurements of the same material in 1983 of 14.33 a ± 0.02 a (P. De Bièvre, P. Gallet and M. Wertz, Int. J. Mass Spectrom., Ion Phys., 51, 1983, 111).²