Dear Colleagues,
Re the CCP4bb most interesting discussion thread initiated by Richard
Gillilan at CHESS I summarise below some relevant references alluded to in
my last email of about 3 weeks ago.
In the acoustic scattering discussion re :-
I.D. Glover, G.W. Harris, J.R. Helliwell and
Dear Colleagues,
Further discussions of this most interesting topic have continued between
Colin and myself off-line. Not least we have basically ended up assembling a
references list for further reading! One such I need to check and my copy of
the relevant book has required me to get a
important. The
answer to the last question appears to be never. The
background-subtracted spot intensities really are the square of the
Fourier transform of the AVERAGE electron density in a unit
cell. Yes,
the arithmetic average. Does not matter where the background comes
from.
Ian,
nearBragg2D does not contain a random number generator. I made the atom
constellations for my DS calculations using an awk script. I would
appreciate it if you could create a constellation of atoms that has the
correlated displacements you are talking about, so that I (and others)
can
James,
nearBragg2D does not contain a random number generator. I made the atom
constellations for my DS calculations using an awk script.
My point was that your 'constellation of points' has to be some kind of random
sampling since it has to be a sampling both over the lattice and over
or
crystal imperfections).
Colin
From: CCP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] On Behalf Of
John R Helliwell
Sent: 27 November 2009 09:49
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] decrease of background with distance?
Dear Richard,
A most
[mailto:owner-ccp...@jiscmail.ac.uk] On Behalf Of Richard Gillilan
Sent: 27 November 2009 02:37
To: Ian Tickle
Cc: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] decrease of background with distance?
David had developed an empirical theory to model the
air, solvent,
Compton
Dear Richard,
A most interesting discussion has ensued!
The balance of elastic versus inelastic scattering becomes the core point re
benefit of moving back the detector as mentioned by Ian. It should be easier
now ie with much more beamtime available to measure this as a function of
wavelength.
.
Regards
Colin
From: CCP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] On Behalf Of
John R Helliwell
Sent: 27 November 2009 09:49
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] decrease of background with distance?
Dear Richard,
A most interesting
The source for the X-ray background are points along the air path
post-collimator including the sample with loop and cryoprotecdant (or
capillary and mother liquor). So the 1/r^2 falloff is
noticable going from
100 mm to 200 mm. The same counts in a 2x2 pixel area is now
seen in a 4x4
bulletin board [mailto:ccp...@jiscmail.ac.uk] On Behalf Of
Ian Tickle
Sent: 26 November 2009 11:20
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] decrease of background with distance?
The source for the X-ray background are points along the air path
post-collimator including the sample with loop
Sent: 26 November 2009 11:54
To: Ian Tickle; CCP4BB@JISCMAIL.AC.UK
Subject: RE: [ccp4bb] decrease of background with distance?
Ian
Maybe - maybe not.
Investigations of acoustic and optical components of diffuse scatter
from proteins were carried out in the 80s and 90s including of course
!
Colin
-Original Message-
From: CCP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] On Behalf Of
Ian Tickle
Sent: 26 November 2009 14:00
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] decrease of background with distance?
Hi Colin
Yes I know, I worked with David Moss at Birkbeck
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
Thank you all for your informative responses!
While examining the effects of unusual beam profiles on data
collection due to capillary optics, I had collected a wedge of data
on a large, high-quality lysozyme crystal at 8 different sample to
detector distances. I restricted the analysis of
Subject: Re: [ccp4bb] decrease of background with distance?
Spots don't fall off with the inverse square law. It is a very easy
experiment to do. Just take exposures at several distances and scale the
data together, noting the correction for air absorption.
A good reference for the underlying
: CCP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] On Behalf Of
Jim Pflugrath
Sent: 24 November 2009 15:25
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] decrease of background with distance?
The source for the X-ray background are points along the air path
post-collimator including the sample
The flux from the spots fall off as the square as well. Assuming that
flux at the detector is linear with respect to measured intensity, I'm
not sure where the benefit would be. I'm also assuming an ideal beam
and ignoring other sources of noise.
James
On Nov 23, 2009, at 2:54 PM,
I mean I'm not assuming an ideal beam.
On Nov 23, 2009, at 2:54 PM, Richard Gillilan wrote:
It seems to be widely known and observed that diffuse background
scattering decreases more rapidly with increasing detector-to-sample
distance than Bragg reflections. For example, Jim Pflugrath, in
That could depend where the beam is focused- if focused on the crystal
then it diverges from that point, like the bulk of the scattered x-rays
that give rise to background. If focused on the detector, it could actually
be convergent over that distance while the scattering is divergent.
Also on
Spots don't fall off with the inverse square law. It is a very easy
experiment to do. Just take exposures at several distances and scale
the data together, noting the correction for air absorption.
A good reference for the underlying theory is Chapter 6 of M. M.
Woolfson's book (1997). But
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