Hi all.

I've been spending some time measuring indium (Lα)  in natural minerals, and (for those of you who tried this) you will be aware of the serious interference with Sn-Lη. There's no other significant x-ray line to use (apart from a minor Lβ4 line) So here comes the problem: when I measure stannite and cassiterite, the minimim "excess" indium concentration correlates very well with the Sn concentration and can be subtracted by a linear approximation. However, when measuring Sn metal, I get a significant additional surplus of indium that I can't explain. I'm pretty certain the the metal doesn't contain indium at the several hundreds of ppm level, as I've analysed several different standard reference materials from a variety of sources. All of the reference metals have this excess and are fairly constant with respect to this additional indium signal.

So what could cause this? I measure background positions on both sides of the peak, however I've been forced to put a background beyond the Sn-Lα peak. I checked for absorption edges, which are fine. I checked for minor metal substitution in cassiterite (notably Fe, Nb) which are not a problem. So what is it? Is the background shape particularly sensitive to the conductivity of the pure metal in contrast to the insulating cassiterite? Is the relative height of the Sn-Lη line influenced by the valency or bonding (metallic versus covalent)? 

I would be interested in any bright ideas to what could cause this.

Best regards, 

Jens

Jens Andersen
Camborne School of Mines
University of Exeter
Cornwall Campus
Tremough
Penryn
TR10 9EZ
01326 371 836