Читать книгу Monument Future - Siegfried Siegesmund - Страница 235

The Mn/Fe counts ratio is essentially a qualitative indicator of elevated Mn levels. For a quantitative result the most straightforward approach is to estimate the mass of Mn. To accomplish this, a suitable calibration standard is required. In this project we used a well-characterized set of mudrock (shales, sandstones) samples (HR_01 – HR_65) provided by the manufacturer of the pXRF instrument. To more closely simulate the desert layer structure, McNeill and Cecil prepared a standard consisting of a thin layer of Mn on a glass substrate (McNeil et al. 2009). In either case the result is the total mass of Mn in the beam. This can be normalized to an areal density by dividing the mass of Mn by the beam area. One drawback of this calibration method is that it is valid only for a specific set of instrument settings such as beam current, standoff distance, etc. Thus, these have to be replicated in the field.