You are referring to the different sources of electronic noise <https://en.wikipedia.org/wiki/Noise_(electronics)> produced by your detector. Frequency analysis of that noise (white noise vs noise at particular frequencies) might tell you something about your detector, but not about your sample. Here I assume you are talking about counting noise, not background due to imperfect crystallinity or sample environment.
Hopefully most noise in a diffraction pattern will simply be the statistical noise in counting individual photons or neutrons. With low counts that will indeed have different distributions; in the background, with asymmetric Poisson statistics with a cut-off at zero counts, and in strong peaks, with a transition to a symmetrical normal distribution. Fitting (smoothing), and especially Rietveld fitting which constrains the positions and relative intensities of the peaks, will obtain the best estimate of even weak peaks, provided you have a physically realistic model for the scattering and not too much correlation between parameters. For low (neutron) counts, Rietveld assigned weights inversely proportional to the count, which can be justified by statistics, and which helps prevent the important information in weak or absent peaks being swamped by the fit to strong peaks. There have been attempts to shorten scanning time by spending more time on weak peaks, which are "noisier", but in practice that is difficult, if as usual you have a multi-detector that collects the whole pattern at the same time. But weak or absent peaks are indeed more important than strong peaks. I am not sure that I have answered your questions, or even if I have correctly understood them :-) But then you didn't receive many other answers either. Alan. On 24 April 2016 at 19:16, Shay Tirosh <stiro...@gmail.com> wrote: > Dear Rietvelders > > Does the noise in XRD tell something? > > Correct me if I'm wrong but I think the noise on a peak is different then > the noise in baseline. > If this is correct then is there a possibility to identify broad peaks or > very small peaks? using some noise analysis. > Can noise analysis help in better smoothing or fitting? > Distinguishing between different noise types at baseline vs peak (Shot > noise, flicker noise <https://en.wikipedia.org/wiki/Flicker_noise> and > Johnson–Nyquist > noise <https://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noise> > ) may leads to shortening the scanning time, or even to help finding the > appropriate fitting function. > > Please comment > > Shay > > -- > _________________________________________________ > > Dr. Shay Tirosh > Institute for Nanotechnology & Advanced Materials > Bar Ilan University > Ramat Gan, 52900 > Israel > Phone: +972-(0)30-531-7320 > Mobile: +972-(0)54-8834533 > Email: stiro...@gmail.com > _________________________________________________ > > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > Please do NOT attach files to the whole list <alan.he...@neutronoptics.com > > > Send commands to <lists...@ill.fr> eg: HELP as the subject with no body > text > The Rietveld_L list archive is on > http://www.mail-archive.com/rietveld_l@ill.fr/ > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > > > -- ______________________________________________ * Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE * <alan.he...@neutronoptics.com> +33.476.98.41.68 http://www.NeutronOptics.com/hewat ______________________________________________
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