Jim Cline wrote: >Alan??? Are you listening? Armel wrote: >>Bruker providing help to analyze Panalytical data ?-).
You have thrown the bait and I will bite. I am not an employee of a manufacture and as such I am free to implement as I choose into TOPAS-Academic (TA) and I do this without regard to manufacture. TA is not institutionally funded (typical), falls far short of paying its way and thus that classifies it as a hobby. Fundamental parameters in regards to a linear PSD (LPSD) was worked out by myself and Bob Cheary: Cheary, R. W. & Coelho, A. A. (1994). "Synthesising and Fitting Linear Position-Sensitive Detector Step-Scanned Line Profiles". J Appl. Cryst. 27, 673 - 681. To be humble I should say that such a geometrical analysis is significant but not world shattering in its own right. The difficulty is in the massaging of the equations into a form that allows an implementation in a meaningful sense. This is where Bob and I have contributed standing on the shoulders of GIANTS in the field like Jim and Armel. >Last point, what do you mean by vertical divergence? The Topas >manual defines the 'axial divergence' which can be limited by soller >slits, and the 'horizontal divergence in the equitorial plane', which is, >I think, the divergence perpendicular to the axial divergence. >Whether you call it horizontal or vertical depends on whether you >have a horizontal or vertical goniometer . Its best to use the terms axial plane and horizontal plane to avoid confusion. >Is there anybody who has experience with describing peak shapes >using the fundamental parameters approach for a typical X'pert-pro >diffractometer setup with an X'celerator detector (fixed incident >slits, 0.02 rad sollers, no monochromator)? Arie, I don't know about either the Bruker or Panalytical LPSD's but my guess is that modern LPSDs reduces or even removes the parallex aberration which is associated with the depth of the detector. This would sharpen peaks. If this is the case then my feeling is that TA can describe modern LPSD step scanned profiles using the peak stack mechanism and the one_on_x_conv convolution for the case of a flat sample and not using a primary monochromator. In Laurel Basciano case the LPSD aberrations is not noticeable due to the small LPSD window used. Thus Arie's query is still unanswered as no one seems to know how these detectors work or worst still no one reads these mails; maybe the manufacture's specifications are enough to look into. In regards to non-standard configurations and in particular geometry employing a focusing pre-monochromator in a laboratory sense. Such a setup is sensitive to alignment and often the beam is inhomogeneous in wavelength in the horizontal plane. This leads to a noticeable change in expected alpha1 and alpha2 separation at moderate to high angles. Such an effect can be modeled for the case where alpha2 is not removed but it needs more investigation. As usual such an implementation/investigation is non-trivial to do properly. If someone wants to volunteer GOOD data and time then I am willing to collaborate - time permitting. So in addition to Arie's query I would like to know if others have noticed such alpha1/alpha2 anomalies. Alan
