Corresponding data for the more energetic Ba K line are 1.0 to 1.6 mm (50% of the fluorescence signal), 2.4 to 3.8 mm (80% of the signal) and 3.4 to 5.4 mm (90% of the signal). As can be seen from Table 2, a range of depths are relevant to other elements, depending on the energy of the respective X-ray fluorescence line and the mass absorption coefficient of the sample matrix for the line.