, January 15, 2015 12:00 PM
To: Keller, Jacob;CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] X-ray Source Differences (WAS: RE: [ccp4bb] How far does
rad dam travel?)
Jacob,
Background subtraction is unfortunately not as forgiving as you think it is.
You can subtract the background, but you can't
: [ccp4bb] How far does rad dam travel?
Yes, bigger is okay, and perhaps a little better if you consider the effects of
beam/crystal vibration and two sharp-edged boundaries dancing over each other. But
bigger is better only to a point. That point is when the illuminated area of
non-good-stuff
: [ccp4bb] X-ray Source Differences (WAS: RE: [ccp4bb] How far does
rad dam travel?)
Jacob,
Background subtraction is unfortunately not as forgiving as you think it is.
You can subtract the background, but you can't subtract the noise.
This is because noise (by definition) is never the same
-Original Message-
From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Dom
Bellini
Sent: Thursday, January 15, 2015 12:25 PM
To: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] X-ray Source Differences (WAS: RE: [ccp4bb] How far does
rad dam travel?)
Dear Jacob,
To add
: [ccp4bb] How far does rad dam travel?
Yes, bigger is okay, and perhaps a little better if you consider the effects
of beam/crystal vibration and two sharp-edged boundaries dancing over each
other. But bigger is better only to a point. That point is when the
illuminated area of non-good-stuff
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Hi Jacob,
both George Sheldrick and Andrew Leslie explained to me that the
machine I had in mind - a sealed tube generator with a graphite
monochromator - is not really state of the art and merely a technology
from 20 years ago. Hence my comment
Hi Tim, Jacob,
I must admit that I was very surprised by the
suggestion of a top-hat profile for a in-house rotating anode. We have a Rigaku
Fr-E generator, and Rigaku provided a plot of the beam profile for that (with
VariMax-HR Optic) and it is very far from being
the top-hat profile is one of the reasons why inhouse machines produce better
quality data than synchrotrons. However, the often much increased resolution
you achieve at the synchrotron is generally worth more than the quality of the
data at restricted resolution.
Cheers,
Tim
Several
Hi Jacob,
at the beginning of my experience of S-SAD about 10 years ago, it was
not too difficult to do S-SAD phasing with inhouse data provided the
resolution was better than 2.0A, while it did not always work with
synchrotron data. Purely personal experience.
However, the inhouse machines I am
at the beginning of my experience of S-SAD about 10 years ago, it was not too
difficult to do S-SAD phasing with inhouse data provided the resolution was
better than 2.0A, while it did not always work with synchrotron data. Purely
personal experience.
I assume that the synchrotron data were
beam profiles (top-hats?) and lower-noise,
faster detectors (like Pilatus and the new ADSC).
Jacob
-Original Message-
From: James Holton [mailto:jmhol...@lbl.gov]
Sent: Tuesday, December 30, 2014 3:57 PM
To: Keller, Jacob; CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] How far does rad dam
Translate it by 13 microns. And use enough attenuation to get 180
degrees at each position.
The track length of photoelectrons from 1 A X-rays in water, protein,
plastic, and other materials with density close to 1 g/cm^3 and atomic
numbers close to 7 is about 3 microns (Cole, Rad. Res.
Yes, it gets complicated, doesn't it? This is why I generally recommend
trying to use a beam that matches your crystal size.
...or is bigger, right? Diffuse scattering, yes, but more even illumination
might be worth it?
Generally, James, I have a question: what is the nature of the intensity
Yes, bigger is okay, and perhaps a little better if you consider the
effects of beam/crystal vibration and two sharp-edged boundaries dancing
over each other. But bigger is better only to a point. That point is
when the illuminated area of non-good-stuff is about equal to the area
of the
Dear all
In a metal-containing crystal of (say) 200 um x 200 um, and a beam size of 10
um x 10 um, how far will I need to move away from an irradiated part to a fresh
part to obtain an undamaged dataset?
Exposure conditions: 100 % transmission at 10^12 ph/s, 0.1 s exposure, fine
sliced at 0.1
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