Absolute and relative measurement of the .sup.243Am half-life

The half-life of .sup.243Am has been measured by an absolute and a relative method, i.e. by determining the specific activity of .sup.243Am and the specific activity ratio with .sup.241Am. A mixed .sup.241,243Am reference material was produced and certified for its americium mass content and its isotope amount ratios. The characterisation of the mass content of .sup.243Am was established by isotope dilution mass spectrometry using an .sup.241Am spike, produced from highly enriched .sup.241Pu material. The isotope amount ratios n(.sup.241Am)/n(.sup.243Am) and n(.sup.242mAm)/n(.sup.243Am) were measured by thermal ionisation mass spectrometry. Activity measurements were performed by alpha-particle counting at a defined solid angle, as well as high-resolution alpha-particle spectrometry. From the .sup.243Am/.sup.241Am activity and isotopic amount ratios, a value of 16.988 (24) was derived for the .sup.243Am/.sup.241Am half-life ratio. Using a value of 432.6 (6) a for the .sup.241Am half-life, the corresponding .sup.243Am half-life value, 7349 (15) a, is in good agreement with the result obtained from the absolute method, 7342 (14) a. The mean value, 7345 (14) a, agrees well with data from literature and lowers the relative standard uncertainty to 0.2%.