Simon Billinge wrote: >We can resolve the problem by setting 2pi=1!
What school did you go to; thanks for the info. This issue of plotting data is one of those's non-issues drummed up by groups familar with one format but not in another; I would suggest that everyone should be familar with both types of displays. If we had the case where only 1/d is plotted eclusively then a whole lot of useful information would be lost. For example, if I look at a fit of a 2Th plot then I can immediately ascertain the following by looking at the misfits: - Are the low angle peaks fitting properly; if not then something is wrong with either the axial or equitorial divergence corrections. - If the peaks are not fitting at 90 degrees then I know that sample penetration is not being accounted for proeprly. - If variable divergence slits are being used then I know the angle where spill over on a post monochromator takes occurs. You cannot make these deduction from 1/d plots. Bob's "Law of Unintended Consequences" cannot be ignored. Are we to teach crystalographers to ignore data collection - big mistake. Simon also mentioned Fourier transform; FFTs' work in equal data steps so be aware of data conversion. My guess is that most conversion programs do the wrong thing. alan -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Simon Billinge Sent: Thursday, 22 February 2007 2:52 AM To: rietveld_l@ill.fr Subject: Re: Powder Diffraction In Q-Space roughly speaking, historically, Q=2pi/d is used by physicists and S=1/d used by crystallographers and these communities define their reciprocal lattices and Fourier transforms accordingly. With the 2pi in there, Q is the momentum transfer. Without it in there the Laue Equations are much cleaner. Physicists are good at working in reduced units, like setting c=1. We can resolve the problem by setting 2pi=1! S On 2/21/07, Ray Osborn <[EMAIL PROTECTED]> wrote: > On 2007/02/21 9:06, "Jonathan Wright" <[EMAIL PROTECTED]> wrote: > > > 2pi/d just needs a better name than Q? > > I guess, to some extent, this debate depends on whether you are only > interested in talking to other powder diffraction specialists. As a > non-specialist, I would suggest that Q is a more widely used variable - > certainly in the inelastic scattering community, but also I believe in the > liquids and amorphous community, who might be interested in studying > crystallization processes, for example. > > If I want to check the elastic scattering contained within my inelastic > spectrum, it is certainly an inconvenience having to convert from two-theta, > even assuming I know the wavelength. I certainly hope you don't settle on > 10^4/d^2. > > Regards, > Ray > -- > Dr Ray Osborn Tel: +1 (630) 252-9011 > Materials Science Division Fax: +1 (630) 252-7777 > Argonne National Laboratory E-mail: [EMAIL PROTECTED] > Argonne, IL 60439-4845 > > > > -- Prof. Simon Billinge Department of Physics and Astronomy 4268 Biomed. Phys. Sciences Building Michigan State University East Lansing, MI 48824 tel: +1-517-355-9200 x2202 fax: +1-517-353-4500 email: [EMAIL PROTECTED] home: http://nirt.pa.msu.edu/
