Hi, I am going to be in the same boat soon, especially regarding obtaining instrument parameters for a new instrument. But one thing I do know, is that to get the polarization parameter, quartz is not a great standard. For polarization factors, you need something really simple, with heavy atoms and all atoms on centers of symmetry, and with thermal parameters very well constrained, so that you can REFINE the polarization parameters for your machine, particularly when incindent beam monochromators are used. The only problem is, I can't remember what the favorite standard is, or where it can be purchased. I will need to know myself, so I will ask, on behalf of Blaise and myself as well, what is the best standard for refining the polarization of an instrument with monochromatized beam? Thank you! - Kurt
________________________________ From: Mibeck, Blaise [mailto:[EMAIL PROTECTED] Sent: Wed 9/17/2008 12:22 PM To: rietveld_l@ill.fr Subject: Beginer problems, difficulty charecterizing our diffractometer... I am re-learning GSAS to bring Rietveld to my department (for the first time). We have an old Phillips Xpert. I am trying to refine a quartz standard to acquire my profile and instrument parameters for this instrument and have yet to get my Chi^2 below 500. The instrument is not in my direct control. I have caught and asked them to correct a few problems already (dwell time too low, aluminum sneaking into the beam, etc...) and this has helped. I would like not to annoy them any more than I have too. At this point I think my high Chi^2s are mainly due to low angle asymmetric peaks that my fit is not able to copy - the asym is not terrible but may be messing me up. I am getting better results with peak profile functions 3 and 4, but unable to get Chi^2 below 500. My scans go up to 70 degrees 2theta. I would like to tell the people caring for the instrument that my problem is on their end, but I am not confident in my own refining skills to say this. When I work with the tutorials or standard data from my graduate school experiment I am ok - I think I am proceeding in a reasonable way, although I can get stuck here and there. I would like to find out if I am doing something incorrectly or if the problem is instrument related. I hate to bug one of you but wonder if I could get someone to look at my work?? Is there a better forum for asking for this kind of help? Kindest regards to all of you, Blaise * * * * * * * * * * * * * Blaise Mibeck Research Scientist Energy & Environmental Research Center University of North Dakota 15 North 23rd Street, Stop 9018 Grand Forks, ND 58202-9018 Phone: (701) 777-5077 Email: [EMAIL PROTECTED]
