Hi Richard

The only ones I'm aware of is this one: Acta Cryst. (1990). A46,
315-320, the one mentioned by Colin:  Acta Cryst. (1991). B47, 960-968,
and this review: Crystallography Reviews, (2003), 9, 229-277.

Cheers

-- Ian 

> -----Original Message-----
> From: [log in to unmask] 
> [mailto:[log in to unmask]] On Behalf Of Richard Gillilan
> Sent: 27 November 2009 02:37
> To: Ian Tickle
> Cc: [log in to unmask]
> Subject: Re: [ccp4bb] decrease of background with distance?
> 
> 
> 	David had developed an empirical theory to model the 
> air, solvent,
> 	Compton & acoustic contributions and correct the 
> integrated data for
> 	these, without background correction of course since 
> the optic DS
> 	background was ultimately to be our data! 
> 
> ...
> 
> Hi Ian, did David publish this theory somewhere? I'd love to 
> get a reference.
> 
> 
> 			
> 			
> 			
> 
> 
> 		I'm genuinely confused by this because I 
> thought the whole point of
> 		modern focusing optics (or at least the 
> confocal mirror design) is to
> 		focus the beam onto (or close to) the sample, 
> in which case 
> 		wouldn't the
> 		photons diverge from the 'virtual source' 
> (actually a real 
> 		image of the
> 		real source) at the crystal, instead of from 
> the real source?  So then
> 		Bragg spots (and therefore also the acoustic DS) should 
> 		diverge from the
> 		position of this virtual source?
> 
> 		Cheers
> 
> 		-- Ian
> 
> 
> 
> 
> This does seem confusing now. Here at CHESS, focus is either 
> at the collimator (just upstream of the sample), or, in the 
> case of capillaries, on the sample. In rare cases, on the 
> detector.  True, the focal spot would be a virtual source 
> and, if the spot is reflected by an ideal crystal, that 
> wouldn't change anything. But it is a very well collimated 
> source even though it is slightly divergent (by a few mrad at 
> most) ... this is in contrast to background scatter where 
> photons are emitted in the whole q range (assuming it is 
> "that kind" of scatter). So maybe it is more accurate to say 
> Bragg reflections and background scatter are two rather 
> different kinds of sources located at the crystal. 
> 
> Pardon my ignorance, but how can lattice phonons be a 
> significant effect at low temperature? I presume the 
> correlated displacements you refer to must be phonon modes 
> frozen in place to create static disorder or something like 
> that ... or perhaps stuff is moving more than I think at 100 K.
> 
> Richard
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 


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