Samarium

Only one α-particle is produced per ¹⁴⁷Sm, whereas six to eight are formed in the Th and U decay series. Therefore, Sm can often be neglected as a source of radiogenic helium. In rare cases, however, Sm can be extremely enriched in apatite, and does significantly affect the age. HelioPlot can switch between (U-Th)/He and (U-Th-Sm)/He dating by selecting the appropriate option in Options → Input. If (U-Th-Sm)/He is selected, Sm will be used as the colour code for the error ellipses. Samples with missing Sm data are coloured white. Sm is used for the age calculations even if the (U-Th)/He option is selected. If the Sm data are complete, the geometric mean Sm concentration is used as a common reference for the ternary diagram and logratio plot. If any of the Sm compositions is missing, the ternary diagram and logratio plot will use a reference value of zero.