X-ray Standing Waves and the critical sample thickness for Total-reflection: X-Ray Fluorescence analysis

The intensity of a TXRF signal is affected not only by absorption, but also by interference due to standing waves. These two phenomena can lead to contradictory requirements of sample thickness. Their effect was investigated theoretically for three kinds of matrix and various thickness distributions. It was shown that large errors can be made if an internal standard is used which is not distributed homogeneously through the sample.