Samarium 147 dating
The determinations since 1960 have converged on close agreement between the two primary determination techniques used in direct physical counting experiments—ionization chambers and liquid scintillation counters, and with radioisotope age comparisons using two meteorites.
Thus the Sm half-life value of 106 ± 0.8 Byr has now been adopted for standard use by the uniformitarian geological community.
The stunning improvements in the performance of mass spectrometers during the past four or so decades, starting with the landmark paper by Wasserburg et al.
In any case, the determined half-life of Sm has been shown to be dependent on the thicknesses of the Sm counting source and the detector.
There is also evidence decay rates of the radioisotopes used for rock dating have not been constant in the past.
This value is based on the weighted average of four direct counting determinations in the period 1961–1970 and the recalibration in the 1970s of Sm-Nd model ages of two meteorites by forcing them (essentially by circular reasoning) to agree with their Pb-Pb isochron and model ages.
However, direct counting experiments in 2003 determined the Sm half-life value was 10% or more longer at 117 ± 2 Byr.