Yes; it's a case of trying to distinguish between a few boulders and lots of pebbles; the total volume isn't the issue. What I'm looking at is something like surface/volume ratio, but with "surface" being path-dependent and gradual. For a nearest-neighbor path, only the top monolayer of atoms are on the surface. For a 5 angstrom path, the transition region from "surface" to "core" extends 5 angstroms in. But that more sophisticated definition of "surface" doesn't change the fact that the dominant dependence is 1/R, so that should address the issue. --Scott Calvin Sarah Lawrence College On Oct 25, 2010, at 4:43 AM, Matt Newville wrote:

Hi Scott,

That's a pretty amazing use case.

But I'm not sure I understand the issue exactly right. I would have thought the volume (r**3) was the important physical parameter, and that a 1000nm particle would dominate the spectra over 3nm particles. Or is it that you are trying to distinguish between 1 very large crystal or 100s of smaller crystals? Perhaps the effect you're really trying to account for is the surface/volume ratio? If so, I think using Matthew Marcus's suggestion of using 1/r (with a safety margin) makes the most sense.

--Matt