Following up on the original post, I was recently asked to give a popular account of 100 years of X-ray diffraction in about 6 minutes :) This was broadcast on All India Radio from New Delhi on the 12th April across India, but the conservative estimates suggest that no more than 5 persons heard it live. I have a mp3 of the same (~6 MB). I will post it on my Facebook today. It will also be available on the Facebook of our Centre- National Centre for Cell Science, Pune, hopefully posted on Monday or Tuesday.
Shekhar On Sat, Apr 20, 2013 at 9:37 AM, James Holton <jmhol...@lbl.gov> wrote: > > It was the observation that atoms have "size". > > Rutherford's alpha-particle experiment had shown that the nucleus was > incredibly small, very much smaller than the distances between atoms, > bringing about the "solar system" idea, which right away came into question > because such atoms would produce synchrotron radiation and the electrons > would rapidly decay from their orbits. So, every nanosecond that the > universe has not tuned itself into powdered neutronium is evidence against > electrons in "orbit". I think it was Laue who then proposed that the > electrons must be bound very close to the nucleus (somehow). Making the > atoms very sharp points, and separated from each other by vast distances > (relative to their size). However, if the electrons really were confined > to very sharp points, then the x-ray diffracted intensities from things > like perfect rock salt crystals would not fall off with increasing > sin(theta)/lambda. They would be relatively constant (much like the > scattering profile of Rutherford's experiment). This was explained away as > thermal vibrations "blurring" the atomic positions, making them look like > they have "size", and causing the spots to fade with increasing resolution. > > What Debye showed was that the temperature-dependence of this falloff was > insufficient to give the atoms zero size, even when extrapolated to > absolute zero (yes, they had liquid air in 1914), and this residual "size" > was still comparable to bond lengths. That meant the electrons really were > distributed in a "cloud" very far from the nucleus, and apparently not > falling in. The only explanation is that the electron must be > de-localised. And that is a quantum effect. > > I always thought that the paper Debye (1914) Ann. Phys. 348, 49-92 is > perhaps one of the most remarkable in all of science. It is the original > reference for the B factor, the Lorentz factor, and also the paper that > ended determinism. > > At least, that is how I understand it. I had to return my English > translation of the Debye paper to the library. I'll order my own copy. > > -James Holton > MAD Scientist > > > > On Fri, Apr 19, 2013 at 2:38 PM, <colin.n...@diamond.ac.uk> wrote: > >> James >> >> In 1915, I thought Debye and Scherrer were testing for interference >> between the electrons in different orbits within atoms. This was in order >> to test the Bohr model. They got rings but they were powder diffraction >> rings. The method never did identify planetary type orbitals. However Debye >> eventually adjusted his aims and the method did become useful despite "the >> requirement for objects to force themselves into ordered arrays" >> >> Was there some other key observation Debye made in 1915 which you refer >> to? >> >> Colin >> >> >> >> >> -----Original Message----- >> From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of >> James Holton >> Sent: 19 April 2013 18:27 >> To: ccp4bb >> Subject: Re: [ccp4bb] popular piece on X-ray crystallography >> >> Because there is never more than one photon "in flight" at any given >> time. Even at 1 photon/s, we still eventually get spots. >> >> Atoms also don't emit synchrotron radiation, despite there being charged >> particles accelerating around their little "orbits" in there. >> >> But yes, in 1913, people were still hoping there was another explanation >> for these two observations, other than that pesky quantum theory. It was >> in 1915 that Debye made the key observation that collapsed determinism as >> we knew it. I don't think he was very happy about that. >> Neither was Einstein. >> >> -James Holton >> MAD Scientist >> >> On 4/19/2013 9:43 AM, Tim Gruene wrote: >> > -----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-invi >> >>>>>> si >> >>>>>> >> >>>>>> >> > 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----- >> >> -- >> 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 >> >> >> >> >> > -- Shekhar C. Mande (शेखर चिं मांडे) Director, National Centre for Cell Science Ganeshkhind, Pune 411 007 Email: shek...@nccs.res.in, direc...@nccs.res.in Phone: +91-20-25708121 Fax:+91-20-25692259
