Absolute and relative measurement of the 243 Am half-life
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Absolute and relative measurement of the 243Am half‑life M. Marouli1 · S. Pommé1 · V. Jobbágy1 · H. Stroh1 · R. Van Ammel1 · A. Fankhauser1 · R. Jakopič1 · S. Richter1 · Y. Aregbe1 · M. Crozet2 · C. Maillard2 · C. Rivier2 · D. Roudil2 Received: 16 September 2020 / Accepted: 4 October 2020 © The Author(s) 2020
Abstract The half-life of 243Am has been measured by an absolute and a relative method, i.e. by determining the specific activity of 243 Am and the specific activity ratio with 241Am. A mixed 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 243Am was established by isotope dilution mass spectrometry using an 241Am spike, produced from highly enriched 241Pu material. The isotope amount ratios n(241Am)/n(243Am) and n(242mAm)/n(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 alphaparticle spectrometry. From the 243Am/241Am activity and isotopic amount ratios, a value of 16.988 (24) was derived for the 243 Am/241Am half-life ratio. Using a value of 432.6 (6) a for the 241Am half-life, the corresponding 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%. Keywords Half-life · 243Am · Nuclear safeguards · Nuclear forensics · Spike reference material · Isotope ratio
Introduction The decay constant λ establishes the link between the number of atoms N of a particular radionuclide in a sample and their expected radioactive decay rate A, i.e. λ = A/N [1]. The value of λ-or inversely the half-life T1/2 = ln(2)/λ-is invariable in space and time, in spite of recent claims of variability in decay rate measurements erroneously ascribed to solar influences [2–11]. Accurate values for the decay constant or half-life of trans-uranium nuclides are required for accounting of nuclear material, assay of targets used in nuclear physics experiments, and characterisation of isotopic mixtures for radioanalytical purposes. Whereas mass spectrometry is the most accurate measurement method to determine isotope ratios in nuclear material, also relative
* S. Pommé [email protected] 1
European Commission, Joint Research Centre (JRC), Geel, Belgium
Commissariat à L’Energie Atomique Et Aux Energies Alternatives (CEA), DES, ISEC, DMRC, University of Montpellier, Marcoule, France
2
activity measurements can be applied with good accuracy provided that the ratio of the decay constants of the isotopes are well known. A coordinated research project of the IAEA [12] has identified a need for more accurate decay data for 243Am, comprising the half-life value as well as the alpha and gamma emission characteristics. The longest-lived and most common isotopes of americium, 241Am and 243Am, have halflives of
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