Simply on grounds that even a single photon can get diffracted (remember the photon counting multiwire detectors?). The phenomenon might be best described as something like a annihilation-creation process a la Feynman.
Much of this has been discussed on board before. Mini-summary: 'Multiphoton' somehow invokes at least in my mind necessary inter-photon coherence (to maintain phase relations) between multiple scattered photons, which is in general not the case nor necessary. The Bragg equation pictures showing 2 incoming x-rays are very deceiving. They should be seen as a help to understand the phase relation for the electric field vector of the ONE incoming photon resonating multiple atoms' electrons. The new photon then emerges based on a probability function proportional to the structure factors. You just can't predict which one it will be. That 3d (squared) probability distribution - after you have collected many photons - is your diffraction pattern. Chapter 6 introduction... Best, BR -----Original Message----- From: Tim Gruene [mailto:t...@shelx.uni-ac.gwdg.de] Sent: Friday, April 19, 2013 9:44 AM To: b...@hofkristallamt.org Cc: Bernhard Rupp (Hofkristallrat a.D.); CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] popular piece on X-ray crystallography -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hello Bernhard, could you explain this? A photon is the exchange particle of the electromagnetic force, i.e. as soon as you have more than two charged particles interacting there is more than one photon - why is it incorrect to use the term "multi-photon process" in the context of X-ray diffraction? Cheers, Tim On 04/19/2013 06:19 PM, Bernhard Rupp (Hofkristallrat a.D.) wrote: > However, a reviewer could reject the method on theoretical grounds > - the explanation of X-ray diffraction as a multi-photon process is > not correct.... > > BR > > -----Original Message----- From: CCP4 bulletin board > [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Peter Artymiuk Sent: > Friday, April 19, 2013 7:11 AM To: CCP4BB@JISCMAIL.AC.UK Subject: > Re: [ccp4bb] popular piece on X-ray crystallography > > Just to clarify, Jeremy was not being serious, but imagining what an > awkward / obnoxious grant reviewer might have said in 1913. But your > points would be valuable in rebutting such a view > > Pete > > > > On 19 Apr 2013, at 11:28, Navdeep Sidhu wrote: > >> Dear Pet, >> >> On the contrary, far as I know, nature seems to require most solids >> we see around us to be crystalline. And much of the rest is either >> gaseous or plasma. Hence, by the reasoning proposed, we are led to >> suspect a different conclusion: that it's studies dealing with the >> remaining state that have "little general applicability as the >> requirement for objects to force themselves into" the disordered >> arrays of the liquid state "is an absurd limitation." (However, I'd >> support funding it nevertheless.) >> >> Best regards, Navdeep >> >> >> --- On Fri, Apr 19, 2013 at 10:14:04AM +0100, Peter Artymiuk >> wrote: >>> Another of my colleagues, Jeremy Craven, is an NMR spectroscopist >>> and > bioinformatician. He is in referee mode at present and comments: >>> >>> >>>> From: Jeremy Craven <c.j.cra...@sheffield.ac.uk> Date: 19 April >>>> 2013 10:05:18 GMT+01:00 To: Peter Artymiuk >>>> <p.artym...@sheffield.ac.uk> Subject: Re: Fwd: popular piece on >>>> X-ray crystallography >>>> >>>> I suspect this technique will have little general applicability as >>>> the > requirement for objects to force themselves into ordered arrays is an > absurd limitation. I would not support funding it. >>>> >>>> Jeremy >>> >>> >>> I fear he may be right >>> >>> best wishes Pet >>> >>> >>> >>> >>> On 19 Apr 2013, at 09:53, David Briggs wrote: >>> >>>> Following on from that - readers may be interested in Stephen >>>> Curry's post in the Guardian, regarding the Crystallography exhibit >>>> at the London Science Museum. >>>> >>>> http://www.guardian.co.uk/science/occams-corner/2013/apr/19/1 >>>> >>>> >>>> regards, >>>> >>>> Dave >>>> >>>> ============================ David C. Briggs PhD >>>> http://about.me/david_briggs >>>> >>>> >>>> On 19 April 2013 09:44, Peter Artymiuk <p.artym...@sheffield.ac.uk> > wrote: >>>>>> >>>>> >>>>> Dear all >>>>> >>>>> In Britain there is a free newspaper that you can pick up on buses > called the Metro. My colleague Geoff Ford pointed out this short > feature on the history X-ray crystallography in last Monday's Metro > newspaper. I think it's rather good. >>>>> >>>>> http://www.cosmonline.co.uk/blog/2013/04/14/conquering-realm-invis >>>>> i >>>>> >>>>> ble >>>>> >>>>> best wishes Pete >>>>> >>>>> >>>>> >>>>> Prof Peter Artymiuk Krebs Institute Department of Molecular >>>>> Biology & Biotechnology University of Sheffield Sheffield >>>>> S10 2TN ENGLAND >> >> >> --- Navdeep Sidhu Departments of Structural Chemistry & Pediatrics II >> University of Goettingen Office Address: Institute of Inorganic >> Chemistry Tammannstrasse 4 37077 Goettingen Germany >> Email: nsi...@shelx.uni-ac.gwdg.de Phone: +49 551 39 33059 Fax: >> +49 551 39 22582 Dept. Homepage: http://shelx.uni-ac.gwdg.de/ >> --- > > Prof Peter Artymiuk Krebs Institute Department of Molecular Biology & > Biotechnology University of Sheffield Sheffield S10 2TN ENGLAND > - -- - -- Dr Tim Gruene Institut fuer anorganische Chemie Tammannstr. 4 D-37077 Goettingen GPG Key ID = A46BEE1A -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iD8DBQFRcXQyUxlJ7aRr7hoRAm2MAJ92WHxpnCeuwTDw/kcc6Qdy4ynBpgCgooRr MN2Rm2CU2N95Sz4Epd0lEj8= =Ai1+ -----END PGP SIGNATURE-----
