Apologies for the late posting (been away). Interesting question from James and an interesting answer from Ian!
There should be a radiation pressure effect here resulting in a transfer of energy and momentum to the sample. The effect is very small (the term includes flux density divided by speed of light). Although this will not make your crystal fly away, the effect is proposed for space travel (using large "solar sails"). A very small change in energy of the photon results. This can be explained by quantum or more classical theory. The question referred to elastically scattered photons. In fact the Compton effect could also be considered an elastic scattering phenomena as the total energy and momentum of the particles (photon plus electron) is conserved. There is confusion about the terminology here between different disciplines. The difference is that a significant amount of the photons energy is transferred to the electron. Colin -----Original Message----- From: CCP4 bulletin board [mailto:[EMAIL PROTECTED] Behalf Of Ian Tickle Sent: 31 May 2007 10:53 To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Is anomalous signal a different wavelength? I think it's to do with the Uncertainty Principle. You can't say for sure that a particular X-ray photon has gone off in that direction (if you could you would know both its position and momentum accurately which is not allowed). If you integrated the momentum over all possible outcomes I'm sure you would find that it's conserved (it has to be in an elastic collision). -- Ian > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Murray, James W > Sent: 31 May 2007 10:30 > To: CCP4BB@JISCMAIL.AC.UK > Subject: RE: [ccp4bb] Is anomalous signal a different wavelength? > > > Dear All, > > While we are talking about X-ray scattering, I have another > question. If an X-ray is elastically scattered from an > electron at an angle theta, its energy is the same is the > incoming X-ray. However, the momentum is not the same, as it > now has a component in a perpendicular direction (see fig > below). As I don't believe that the conservation of momentum > really is violated, what is the source of the discrepancy? > > Contrast this with most textbook descriptions of Compton > scattering, where the X-ray loses energy and the electron > gains kinetic energy. > > best wishes > > James > > X-ray --------> e- > \ > \ > \ > > > Dr. James Murray > Biochemistry Building > Department of Biological Sciences > Imperial College London > London, SW7 2AZ > Tel: +44 (0)20 7594 5276 > > > > > > Disclaimer This communication is confidential and may contain privileged information intended solely for the named addressee(s). It may not be used or disclosed except for the purpose for which it has been sent. If you are not the intended recipient you must not review, use, disclose, copy, distribute or take any action in reliance upon it. If you have received this communication in error, please notify Astex Therapeutics Ltd by emailing [EMAIL PROTECTED] and destroy all copies of the message and any attached documents. Astex Therapeutics Ltd monitors, controls and protects all its messaging traffic in compliance with its corporate email policy. The Company accepts no liability or responsibility for any onward transmission or use of emails and attachments having left the Astex Therapeutics domain. Unless expressly stated, opinions in this message are those of the individual sender and not of Astex Therapeutics Ltd. The recipient should check this email and any attachments for the presence of computer viruses. Astex Therapeutics Ltd accepts no liability for damage caused by any virus transmitted by this email. E-mail is susceptible to data corruption, interception, unauthorized amendment, and tampering, Astex Therapeutics Ltd only send and receive e-mails on the basis that the Company is not liable for any such alteration or any consequences thereof. Astex Therapeutics Ltd., Registered in England at 436 Cambridge Science Park, Cambridge CB4 0QA under number 3751674
