Re: [ccp4bb] X-ray photon correlation length

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CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

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Subject: Re: Obtaining relationships between two cross rotation solutions?
From: Eleanor Dodson ccp4 {- at -} YSBL {- dot -} YORK {- dot -} AC {- dot -} UK
Date: 2009-02-04

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Date: 2009-02-04

Subject: Re: X-ray photon correlation length
From: Dirk Kostrewa kostrewa {- at -} LMB {- dot -} UNI-MUENCHEN {- dot -} DE
Date: 2009-02-04

Hi James,

Am 03.02.2009 um 17:38 schrieb James Holton:

> Hey Dirk,
>
> You're wrong. ;)

okay, thanks a lot! ;-)

> The remarkable part of this is that the integrated spot intensity
> (photons) is essentially invariant with how you divide up the unit
> cells into mosaic domains. Well, okay, if N=1, then you don't
> really have a crystal but an amorphous solid (seen a lot of those),
> so I should qualify that so long as N > ~1000, it doesn't matter if
> m is 1 or 10^12, the integrated spot intensity (photons) is still
> proportional to the total number of unit cells in the crystal. This
> was first shown by C. G. Darwin (1914) so I don't blame you if you
> can't find the original reference. However, "Darwin's Formula" can
> be found in most modern textbooks. It is Equation 9.1 in Blundell &
> Johnson (1976) and Equation 4.31 in Drenth (1999). You will note
> that the mosaic spread is not part of this equation.

thanks for the pointer - I found Darwin's formula both in my copy of
Blundell & Johnson and in Giacovazzo's "Fundamentals of
Crystallography", chapter 3.14. It is really interesting to see that
the deposited total energy on a detector for a reflection is indeed
proportional to V and thus to N.

> I understand it was W. L. Bragg et al. (1921) who confirmed that the
> absolute scattered intensity from rock salt does indeed obey
> Darwin's Formula. I confirmed it recently for lysozyme on my
> beamline, but never published it as I figured I had been scooped 86
> years earlier.

... such things happen to all of us sooner or later ...

> The distribution of unit cells into mosaic domains does become
> important if the extent of a mosaic domain starts to become large
> compared with the attenuation length of the x-ray beam, then one
> must invoke the dynamical theory. Darwin derived equations for the
> dynamical case as well, but these almost never apply to protein
> crystals. They are just too small.

many thanks again for your explanations!

Best regards,

Dirk.

*******************************************************
Dirk Kostrewa
Gene Center, A 5.07
Ludwig-Maximilians-University
Feodor-Lynen-Str. 25
81377 Munich
Germany
Phone: +49-89-2180-76845
Fax: +49-89-2180-76999
E-mail: kostrewa@lmb.uni-muenchen.de
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CCP4bb navigation

CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

Previous message:
Subject: Re: Obtaining relationships between two cross rotation solutions?
From: Eleanor Dodson ccp4 {- at -} YSBL {- dot -} YORK {- dot -} AC {- dot -} UK
Date: 2009-02-04

Next message:
Subject: MX-beamtime at BESSY-Berlin, period: July/2009 - June/2010, Deadline March 1, 2009
From: Uwe Mueller umue {- at -} BESSY {- dot -} DE
Date: 2009-02-04