Simple methods for calculating activity of a parent-progeny system.

Based on the original work of Rutherford (Radio-activity, 1905) and Bateman (Proc Camb Philos Soc 15:423-427, 1910), the authors designed two schemes consisting of explicit equations as simple methods for accurately obtaining activity of 90 Sr and 90 Y before they reach secular equilibrium. Application of the methods to the 90 Sr/90 Y system where 90 Sr and 90 Y are not in equilibrium will substantially reduce the time needed for determining activity of 90 Sr because neither sequential measurements of 90 Sr or 90 Y (up to about 2 weeks) nor waiting for 90 Sr and 90 Y to reach equilibrium (more than 3 weeks) will be needed. We also implemented the explicit equations for decay/ingrowth correction of progeny's activity and applied them to the 95 Zr/95 Nb system. Using the equations, the authors corrected activity concentrations of 95 Nb to a designated reference time from the activity concentrations measured from samples at different times, for instance, 2, 8, 15, and 29 days after a reference time. During those measurement times, 95 Nb and 95 Zr were not in equilibrium. The corrected 95 Nb activity concentrations were within an accuracy of - 10%.