Richard
I think the sharp spot is just small angle scattering (e.g. from domain
boundaries) resulting from the beam hitting one of the defining
apertures in your collimation system. If you ray trace the beam from the
last defining aperture, through the guard aperture then to the detector
you should get an area of high background where the guard aperture does
not cut this off and it is not covered by the beamstop. It then drops
off as the beamstop comes in to play appearing to give a sharp spike. In
fact, it is quite well set up with the beamstop not overly large.
The appearance of a very diffuse ring for the scatter from nitrogen is
due to the fact that the beamstop cuts off the air scatter, for the
parts of the beam nearer the beamstop.
Cheers
Colin
-----Original Message-----
From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of
Richard Gillilan
Sent: 27 November 2007 16:40
To: [log in to unmask]
Subject: Re: [ccp4bb] To bathe or not to bathe.
Oops, sorry. The x axis of the previous plot is actually not resolution,
but Q. My bad.
Richard
On Nov 27, 2007, at 11:26 AM, Richard Gillilan wrote:
> Just a couple small images that may be of interest. The x scale is
> resolution in Angstroms, the y scale is intensity (arbitrary units). I
> don't recall if the plot is corrected for CCD pedestal values, so the
> difference is not quite as dramatic as x49, still very nice clean
> background if you are looking for a faint signal.
>
> The CCD images below are equal exposures shown with equal contrast
> settings:
>
> <HeN2.tiff>
> <HeN2imgs.tiff>
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