Bernard I guess this came from "Aren't detwinning methods appropriate only in the case of true twin domains which are larger than the X-ray photon correlation length in order for the assumption to be valid that |F|^2 from each domain can be summed? This wouldn't give rise to the apparent 'diffuse scatter' phenomenon." I think this is normally called coherence length. Probably best not to think of photons at all but waves (though there is an equivalent quantum mechanical treatment based, as V Nagarajan says, on the uncertainty principle). I don't think the domains have to be larger then the correlation (sorry coherence) length of the incident x-rays in any case. They have to be large enough to give an intensity which can be integrated. If smaller domains are present, the intensity just spread out a bit more.When the domains are very large, the size of the spots would be determined by the incident beam properties. The article cited some years ago on CCP4BB gives a primer on all this J. Phys.: Condens. Matter 16 (2004) 5003-5030 PII: S0953-8984(04)75896-8. Coherent x-ray scattering Friso van der Veen1,2 and Franz Pfeiffer1
http://www.iop.org/EJ/article/0953-8984/16/28/020/cm4_28_020.pdf?request -id=8848d3f0-5a4b-4ffe-8ea4-c1eabfaf1657 Cheers Colin ________________________________ From: CCP4 bulletin board [mailto:[email protected]] On Behalf Of Bernhard Rupp Sent: 29 January 2009 17:51 To: [email protected] Subject: [ccp4bb] X-ray photon correlation length I always wondered - how is the X-ray photon correlation length defined and where do I find it? This is not the interaction length, I assume. So, to the physicists: How large is the 'X-ray photon correlation length' for a given wavelength in a given material? I had the impression that the term photon correlation refers to the time correlation of the scattering such as in photon correlation spectroscopy... Best regards, BR <DIV><FONT size="1" color="gray">This e-mail and any attachments may contain confidential, copyright and or privileged material, and are for the use of the intended addressee only. If you are not the intended addressee or an authorised recipient of the addressee please notify us of receipt by returning the e-mail and do not use, copy, retain, distribute or disclose the information in or attached to the e-mail. Any opinions expressed within this e-mail are those of the individual and not necessarily of Diamond Light Source Ltd. Diamond Light Source Ltd. cannot guarantee that this e-mail or any attachments are free from viruses and we cannot accept liability for any damage which you may sustain as a result of software viruses which may be transmitted in or with the message. Diamond Light Source Limited (company no. 4375679). Registered in England and Wales with its registered office at Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0DE, United Kingdom </FONT></DIV> -- Scanned by iCritical.
