Year
2008
Abstract
IRMM has been highly involved in the measurement of the half-life of 241Pu, the shortest commonly encountered isotope of plutonium, since the mid 1970’s. At this time an amount of plutonium, highly enriched in the 241 isotope was obtained and a series of measurements of the amount of this isotope relative to the longer-lived isotopes 239 and 240 was begun. A number of measurements of the double ratio [n(241Pu)/n(240Pu)]/[n(240Pu)/n(239Pu)] were carried out in 1976 and continued 20 years later. The double ratio compensates for any mass-fraction effects in the isotope ratio measurements. The half-life obtained from these measurements carried out up to 1996 was previously published. A new series of measurements carried out in 2006 on the same material using improved measurement techniques has now corrected the value published in 1996. At the same time the method of calculating the half-life from the heterogeneous set of mass-spectrometry measurements over 30 years has been critically overhauled with the aim of producing a half-life value that is solidly based on metrological foundations. The results of the measurements will be presented and the method applied outlined.