Fig. 2

Wavelength scan simulation performed by PfE around Th Mα (a), U Mβ (b), Pb Mα (c), and Eu Lα (d) peaks. The L value (mm) used in the JEOL electron microprobe is the length of the refracted X-ray from the sample to the analyzing crystal. A representative chemical composition of lunar zirconolite measured in this study was used for the simulation under the same analytical condition for quantitative analyses. Interference correction was applied based on the simulation results. No significant interferences were observed for Th Mα (a). More detailed wavescan simulations were performed for U Mβ and Pb Mα (insets of b and c). Secondary fluorescence of K Kα from the adjacent K-feldspar is expected to increase K concentrations to ~ 0.25 wt % in zirconolite (Fig. S3), which may interfere with U Mβ (b). The interference of Y Lγ2,3 is unavoidable (c). Note that the wavescan simulation data are likely to be different from the actual wavescan on the sample and the interferences of Th and K on U and Y on Pb should be corrected with appropriate correction factors. After correction of Nd, Pr, and Mn interferences on the Eu Lα peak, the Eu concentrations became below the detection limit