IUGS–IUPAC recommendations and status reports on the half-lives of ⁸⁷Rb, ¹⁴⁶Sm, ¹⁴⁷Sm, ²³⁴U, ²³⁵U, and ²³⁸U (IUPAC Technical Report)

The IUPAC–IUGS joint Task Group “Isotopes in Geosciences” (TGIG) has evaluated the published literature on the half-lives of six long-lived, geologically relevant radioactive nuclides. Where conflicting literature estimates are present, it is necessary to first identify any systematic bias in accordance with metrological traceability and to exclude the biased estimates from further consideration. The TGIG recommends three robust half-life estimates: 49.61 ± 0.16 Ga for 87 Rb, corresponding to a decay constant λ ( 87 Rb) = (1.3972 ± 0.0045) × 10 −11 a −1 ; 106.25 ± 0.38 Ga for 147 Sm, and a corresponding decay constant λ ( 147 Sm) = (6.524 ± 0.024) × 10 −12 a −1 ; 4.4683 ± 0.0096 Ga for 238 U, i.e . a decay constant λ ( 238 U) = (1.55125 ± 0.00333) × 10 −10 a −1 . All cited uncertainties have a coverage factor k = 2. For other radionuclides of Sm and U, no unambiguous consensus value can be endorsed at present by TGIG, which limits its evaluation to a status report highlighting unaccounted-for potential sources of bias. The improved repeatability of mass spectrometric measurements has revealed systematic bias effects that had been dismissed as subordinate in the past. These issues can only be resolved by future dedicated investigations.