Fig. 3

MAN background curves for Th (a), U (b), and Pb (c). Background intensities were measured at the Th Mα, U Mβ, and Pb Mα peak positions using a 15 keV electron beam with PETL crystal (channel 3) for natural mineral and synthetic compound standards (green circles; listed in Additional file 4: Table S1) that do not contain Th, U, or Pb, respectively. The data were corrected for continuum absorption and a Z fraction average Z was applied using an exponent of 0.7. A 2nd order polynomial was used to best fit the data. The red circle represents the zirconolite. Further details are described in the main text