Fig. 2.

Signal intensity obtained by ablating different spot sizes (50 and 120 μm) and rastering (120-μm spot, moving at 5 μm s⁻¹) as a function of Sr abundance in a mineral (modified from Fig. 2 in [12]). The ablation rate is 1 μm s⁻¹, and the typical efficiency is 0.05% (e.g. 1 in 2,000 ions that get ablated are counted by the detector). This diagram illustrates that with a 50-μm spot size, only the minerals with >2,000 ppm can be analysed with sufficient precision. Rastering results in slightly better ⁸⁸Sr signals, but its greatest advantage is that the beam does not run out of focus during the analysis, and the ⁸⁸Sr ion current does not decay as with a spot analysis