Richard Gillilan wrote:
Sorry, I meant to say "does divergence add to the reported mosaicity
value." If so, do actual mosaicity and divergence add in quadrature to
give the reported value?
Not sure what denzo does, but in general if you convolute two things
that have a Gaussian distribution, then the result is itself a Gaussian
with width equal to the root-mean-square of the two starting widths
(they add in quadrature). However, if you convolve two things that have
a square or "tophat" distribution, then the result is a trapezoid with
base width equal to the arithmetic sum of the two starting widths (they
just add). On the other hand, the full-width at half-max (FWHM) of the
trapezoid is the greater of the two starting widths (not really "adding"
in any normal way).
Nevertheless, when you are integrating spots you're not interested in
the FWHM, but rather the full width at "baseline" (whatever that
means). Gaussians are "easy" because the FWHM, the width at 1% max, or
whatever width you like will always add in quadrature when you convolute
them, but Gaussians are the only shape that does this.
If I were to guess, I would say that denzo probably uses the
Greenhough-Helliwell formula (international tables C 2.2.7.3 p. 40) for
the rocking width (which assumes everything is a tophat function and
that the beam divergence is an ellipse, not a rectangle) and then just
refines the "mosaic spread" (greek letter eta) in that formula until the
integrated intensity "levels off" based on some criterion.
Again, just a guess.
-James Holton
MAD Scientist
On Aug 6, 2009, at 6:14 PM, Richard Gillilan wrote:
Does anyone know if beam divergence gets included in the mosaicity
values reported by HKL2000?
(i.e. does it add to the measured divergence (in quadrature)?)
Richard Gillilan
MacCHESS
