Project Details Evaluation of Radiogenic Abundance Variations in Selected Elements

Project No.:
Start Date:
01 September 2009
End Date:
30 November 2019


The purpose of this project is to evaluate isotopic abundance variations in selected elements, including Re, Os, Rb, Sr, K, Nd, Sm, Hf, Lu, and Ar in a range of materials, based on peer-reviewed measurements, to create graphical plots of these data, and to provide CIAAW with information to update the Table of Standard Atomic Weights.


Recent developments in inorganic mass spectrometry enable isotope ratio measurement of radiogenic elements at unprecedented precision. A steadily growing body of measurements shows radiogenic isotope abundance variations for elements such as Re, Os, Rb, Sr, K, Nd, Sm, Hf, Lu, and Ar. This raises the question of how far current IUPAC recommendations for the standard atomic weights of these elements and their respective uncertainties incorporate any natural variations in isotope abundances.

In July 2009 and in July 2011, task group members will convene prior to the IUPAC general Assemblies to evaluate published information. Particular attention will be paid to possible sources of systematic bias in the measurement uncertainty, the selection of materials for analysis, and the variability of measured isotope ratios in these materials.� Graphical plots of these data with atomic weight axes, delta scale axes, and mole fraction axes, presented for various types of chemicals and substances, in a manner similar to previous SNIF diagrams.

Recommendations will be incorporated into those generated by the Subcommittee on Isotope Abundance Measurements (SIAM) and they will be sent to CIAAW for approval. Approved changes will be incorporated into the next CIAAW Table of Isotopic Composition of the Elements (TICE) and Table of Standard Atomic Weights (TSAW).

The technical report will complement the earlier IUPAC (SNIF) report “Isotope-Abundance Variations of selected elements” (Pure Appl. Chem. 74:1987-2017, 2002; in which these chemical elements could not be comprehensively covered because of lack of manpower.


September 2012 update – The isotopic abundance variations of the radiogenic elements Re, Os, Rb, Sr, K, Nd, Sm, Hf, Lu, and Ar are being evaluated to determine the variability of the atomic weight. These data will be incorporated in the Commission’s Technical Report of the Table of Standard Atomic Weights. The evaluation of Ar is complete and was approved by the Commission on Isotopic Abundances and Atomic Weights (CIAAW) at the Calgary meeting in 2011 for incorporation in the Table of Standard Atomic Weights 2011. The reports on the remaining elements are still in progress and will be presented to the Commission on Isotopic Abundances and Atomic Weights (CIAAW) for approval at the upcoming Commission meeting in 2013.

May 2013 update – the IUPAC Technical Report titled “Atomic weights of the elements 2011” is published as Pure Appl. Chem., 2013, Vol. 85, No. 5, pp. 1047-1078

July 2014 update – J.K. Bohlke has authored a report on Ar. The manuscript has been submitted to PAC and is in press. Literature reviews are complete for Sr and a report is in preparation. Literature reviews for the remaining elements (Re, Os, Rb, K, Nd, Sm, HF, and Lu) are in progress. The goal is to have this work complete for the next CIAAW meeting and incorporate it in TSAW2015.

Sept 2014 update – The technical report titled “Variation in the terrestrial isotopic composition and atomic weight of argon” is published in Pure and Applied Chemistry 2014, Vol. 86, No. 9, pp. 1421-1432;

Sept 2017 update – In addition to Ar, substantial work has been accomplished for Sr. A publication regarding the natural abundance variation of Sr is currently in preparation and submission is foreseen for 2018.
The established database for crowdsourcing (from project 2014-016-2-200) will be used to complete literature research also for elements such as K, Rb, Nd/Sm.

Sept 2019 update – The substantial work on Ar resulted in a revision of the standard atomic weight for Ar. Currently, data evaluation for a variety of elements resulted in the conclusion that substantial work has to be accomplished especially for Hf and Os. This was a major input on the evaluation of data during the SIAM meeting in Berlin 2019. The final evaluation was accomplished within this year and the final conclusion is currently under revision for the preparation of a subsequent project. 

Nov 2019 update – A Technical report by Steur, Peter P. M. / Yang, Inseok / Kim, Jin Seog / Nakano, Tohru / Nagao, Keisuke / Pavese, Franco, and titled “An inter-comparison of isotopic composition of neon via chemical assays and thermal analyses” is published in Pure and Applied Chemistry 2019, 91(11), pp. 1869-1882;

Project complete

Page last updated: 30 Nov 2019