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:[log in to unmask]]
Sent: Friday, April 19, 2013 9:44 AM
To: [log in to unmask]
Cc: Bernhard Rupp (Hofkristallrat a.D.); [log in to unmask]
Subject: Re: [ccp4bb] popular piece on X-ray crystallography
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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:[log in to unmask]] On Behalf Of Peter Artymiuk Sent:
> Friday, April 19, 2013 7:11 AM To: [log in to unmask] 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 <[log in to unmask]> Date: 19 April
>>>> 2013 10:05:18 GMT+01:00 To: Peter Artymiuk
>>>> <[log in to unmask]> 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 <[log in to unmask]>
> 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: [log in to unmask] 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
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