ABSTRACT
The last section discussed chronometry and how the concentrations of nuclides that are linked by decay can be used to determine the time elapsed since the last chemical purification. In many instances, particularly for short times or more distant genetic relationships, the atom ratios of the related species can be quite small, approaching zero. In those cases, particularly if sample sizes are limited, a radionuclide concentration needs to be determined from very few atoms. This can be done by atom counting or by decay counting and may require a chemical separation to remove an overwhelming background activity.
