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Moderator: Ellery Frahm, [log in to unmask],
Electron Microprobe Lab, University of Minnesota

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Hi Eric,

> One "simple" way for a user to get low totals on EMP is to have the  
> sample out of focus during the analysis.  We find some students  
> focusing with BSE or in transmitted light instead of reflected  
> light, or simply failing to check focus.  With the SX-100 we use an  
> autofocus system but some students turn off that option.  Once the  
> low total is obtained, one should immediately check in reflected  
> light to see if the sample is still in focus after the analysis  
> before moving the sample.

This researcher is experienced enough to check for all those problems,  
and we're talking about bad results on a few specific samples (and not  
others run at the same time) over several sessions.  But I'll still  
advice him to pay extra attention to these points next time.

> Another problem is that students (and sometimes their advisors)  
> handle the sample, imparting oils to the carbon coat and causing  
> charging that is difficult to see if the sample doesn't fluoresce  
> (or we find that the user pays no attention to the flickering or  
> moving luminescence!).  One can find salt crystals in swirls in some  
> cases.  The only check for that is to repolish, reclean (a step that  
> lots of folks forget), recoat, and then immediately reanalyze.

A possibility.  I'll suggest that he repolish and reclean the samples  
in case of their surfaces weren't totally clean.