Relative phase abundances, errors

Figure 10 Gas-phase abundances measured towards the star z Oph of various elements relative to atomic hydrogen (X/H) and normalized with respect to solar abundances (X/H)o plotted versus condensation temperature of these elements. The condensation temperature is the temperature at which 50% of that element is depleted from the gas phase into the solid phase. The error bars on the squares indicate measurement errors only. Representative uncertainties in the solar abundances, oscillator strength and condensation temperature are indicated in the lower left hand corner.

For multi-component phases commonly encountered in mineralogy, it may not be possible to construct precise experimental k-factor curves for all elements due to uncommon element abundances in silicates or to a lack of suitable standards. For example, Ni or Cr can occur in silicates in low concentrations, but sufficient to be detected using an AEM. In such instances, calculated k-factors can be determined based upon theoretical cross-sections for X-ray production [34] and are generally suitable for higher-Z elements (Z>Ti) to within 10% relative error [37]. Alternatively, the relationship shown in equation 5 can be used to advantage in the calculation of uncommon k-factors, though with a concommitant reduction in accuracy due to accumulation of errors in determination of the individual k values. 

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