Dear Loes, thank you very much for your explanation. As agreed I hereby share the conclusive email of your off-list discussion with John Helliwell, and a pointer to your article with its explanation http://dx.doi.org/10.1107/S1399004715011803:
---------------------------------------------------------------------> Hi John, Yes, you are right. Apart from the cos(theta) contribution, which is usually small. Indeed lambda^3/(2*sin(theta) cos(theta)) is approximately 4 times as large when changing the wavelength by a factor 2, and accounting for the fact that then theta changes. So the interference function depends on lambda^3, but for integrated reflections obtained by the rotation method the wavelength dependence becomes lambda^2. Greetings, Loes <---------------------------------------------------------------------- Best regards, Tim On Thursday 26 January 2017 05:58:31 PM Loes Kroon-Batenburg wrote: > Dear Tim, > > That is described by the Laue interference function. The crystal > diffracts in Bragg directions (reflections) at small deviations of the > Bragg angle and in a small solid angle. They depend on lambda and > lambda^2 respectively, and integration over these angles brings a factor > lambda^3 in the diffracted intensity. > > Best wishes, > Loes > > On 01/26/17 17:15, Tim Gruene wrote: > > Dear all, > > > > according to Carmelo Giacovazzo's textbook (eq. 3.41 in the 1st edition), > > the diffraction intensity I(hkl) scales with the wavelength cubed > > (lambda^3). > > > > 1) is there an easy rationale for this dependency? > > 2) does it hold over a wide range of energies? > > 3) does this also hold for neutrons or electrons as radiation source? > > > > Thanks a lot for any helpful comment, > > Tim > > -- > > __________________________________________ > > Dr. Loes Kroon-Batenburg > Dept. of Crystal and Structural Chemistry > Bijvoet Center for Biomolecular Research > Utrecht University > Padualaan 8, 3584 CH Utrecht > The Netherlands > > E-mail : [email protected] > phone : +31-30-2532865 > fax : +31-30-2533940 > __________________________________________ -- -- Paul Scherrer Institut Dr. Tim Gruene - persoenlich - Principal Investigator Biology and Chemistry OFLC/102 CH-5232 Villigen PSI Phone: +41 (0)56 310 5297 GPG Key ID = A46BEE1A
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