Hi, As far as I am concerned, synchrotron x-rays and neutron data could be represented in any x-axis unit without any problem other than the users preference or a convention, but what about the kalpha 1,2 doublet for filtered lab x-rays.
I'd rather continue using 2theta as units for x-axis in my papers using lab x-ray patterns just to keep the "true physical meaning" of all the peaks in my pattern. At least until someone comes up with the program that converts a 2-wavelength pattern collected in 2-theta into a correct pattern in Q, 1/d...... I guess this should be like "time focusing" for TOF patterns isn't it?, except that in lab x-rays both "channels" are merged in only one signal. Maybe the day that detectors with energy discrimination becomes cheap and accurate enough to only read the kalpha1 component of the lab x-rays this discussion should be brougth up again. To me this specifical issue of representing the diffraction patterns is just like calling the monoclinic angle beta or gamma, there are other issues like the one Bob brought up, that are not just the way programmers wrote the programs. Best regards. Leo Dr. Leopoldo Suescun Postodoctoral Appointee Materials Science Division - Bldg 223 - Rm D217 Argonne National Laboratory 9700 S. Cass Ave., Argonne, IL 60439 Phone: 1 (630) 252 9760 Fax: 1 (630) 252 7777 URL: http://www.msd.anl.gov/groups/nxrs/personnel/suescun/index.html -----Original Message----- From: Luca Lutterotti [mailto:[EMAIL PROTECTED] Sent: Wednesday, February 21, 2007 11:30 AM To: rietveld_l@ill.fr Subject: Re: Powder Diffraction In Q-Space As we talk about plotting in Q-space (just for information in Maud is available from few months thanks to Klaus-Dieter advocating for it), I would advocate another "plot option" that I would rather see as a default way of plotting. Looking at the other axis (the intensity) I am asking why we don't introduce the practice to plot in a more useful scale as the root square of the intensity (instead of the usual linear scale). This has several benefits: - the plot will be at iso-error (I recall for who may have forgotten the noise is proportional to the root square of the intensity), so in the residuals you may better evaluate which are the peaks or part well fitted or poor fitted. Otherwise with the linear scale you just see only the bad residuals of the more intense peaks and you may think these are the peaks poorly fitted. Instead most of the time in the true statistical meaning they may be well fitted compare to other. In the square root intensity mode you can evaluate them more unbiased - you see also the small peaks and it is not necessary to enlarge the intensity scale to check them In this regard some people are using the log10 scale plot (normally used for reflectivity measurements). It may enhance more the small peaks but I don't favor it as again you do not compare the fitting of different peak on an equal statistical base. As an image is better than thousand words, as they say, I put together one web page with the comparison of linear/sqrt/log10 scale, Q and 2theta so everyone may take its own conclusion. http://www.ing.unitn.it/~maud/plotoptions/ I would encourage the list to propose a standard way (or advised way) to plot, as it would be not too difficult for the different program to provide a standard way to present the results for the benefit of comparisons. Best regards, Luca Lutterotti
BEGIN:VCARD VERSION:2.1 N:Suescun;Leopoldo FN:Leopoldo Suescun ([EMAIL PROTECTED]) ORG:Argonne National Laboratory - Materials Science Division TITLE:Postdoctoral Appointee TEL;WORK;VOICE:+1 (630) 252-9760 TEL;HOME;VOICE:+1 (630) 910-1562 TEL;WORK;FAX:+1 (630) 252-7777 ADR;WORK:;;9700 S. Cass Ave.;Argonne;Illinois;60439;USA LABEL;WORK;ENCODING=QUOTED-PRINTABLE:9700 S. Cass Ave.=0D=0AArgonne, Illinois 60439=0D=0AUSA URL;WORK:http://www.msd.anl.gov/groups/nxrs/people/suescun.html EMAIL;PREF;INTERNET:[EMAIL PROTECTED] REV:20050630T182807Z END:VCARD
