FIG. 3.

Readings at 1500 V (A–C) and at 1000 V (D–F) of each radioisotope and a mixed source spotted on cellulose support, measured over time. (A, D) ²²⁷Th CPM were plotted and fit according to a one-phase exponential decay. (B, E) ²²³Ra CPM were plotted and fit to a one-phase exponential decay. (C, F) Mixed source of ²²³Ra and ²²⁷Th. For all curves, the initial point is excluded from the exponential fitting to allow the system to reach equilibrium. Error bars indicate standard deviation between triplicates. CPM, counts per minute.