Re: RE: error in peak positions that is linear in theta
Dear Mr. Peter I also faced the same problem as Kurt faced, our diffractometer is the D8-advance model from Bruker... I took the scan using a PSD detector(Lynxeye) and got an increase of the error in peak position with increasing 2theta.. Again, when I extracted the dat file from the raw one i observed the rounded up values of 2theta(up to 2 decimal pt.) in the file. Now will the problem be optimized if I generate 2Theta values using a step which is rounded up upto a higher number of decimal point and replace them in place of my 2theta column? thanking you.. prasun - Original Message - From: Peter Y. Zavalij pzava...@umd.edu Date: Friday, January 9, 2009 7:17 pm Subject: RE: error in peak positions that is linear in theta Kurt, It looks like incorrect step size (difference between actual step size and one that is written in the file) or incorrect distance to the detector. The later may incorrect step size if detector is PSD. I have similar situation with much smaller difference in peak position but the shift (difference between actual and written step size) varies frommeasurement to measurement. Bruker is working on this but so far no solution/cause is known. Your case may be simpler if the difference is constant. Perhaps calibrationof detector or its distance to the sample is needed. Best, Peter Zavalij X-ray Crystallographic Center University of Maryland College Park, MD Office: (301)405-1861 Lab: (301)405-3230 Fax: (301)314-9121 From: Kurt Leinenweber [ku...@asu.edu] Sent: Thursday, January 08, 2009 6:09 PM To: Rietveld_l@ill.fr Subject: error in peak positions that is linear in theta Dear Rietvelders, (I hope this list is appropriate for this question). I am trying to set up a new D8 diffractometer from Bruker, and have it set up with a Vario monochromator focusing on a sample in a capillary. Of course I hope to do Rietveld refinement on the samples eventually. But there is an error in two theta of the peak positions on all samples, and the error is linear in two theta. At 40 degrees the error (measured minus expected) is about 0.020degrees, at 80 degrees the error is about 0.040 degrees, etcetera. Has anyone ever seen anything like this and do you know where it could come from? Thank you very much, - Kurt * Kurt Leinenweber Dept. of Chemistry and Biochemistry Arizona State University Tempe, AZ 85287-1604 phone (480)-965-8853 fax (480)-965-2747 ***
RE: error in peak positions that is linear in theta
Hi all, Does the error maximize at 2-theta = 90 then decrease again? Back when I was an actual crystallographer and used an INEL system, this was observed when the capillary position was not coaxial with the detector (in fact, when it was behind the proper position). Alex Y Dr. Alexandre (Alex) F. T. Yokochi Assistant Professor Department of Chemical Engineering Oregon State University Corvallis, OR 97331-2702 Voice: (541) 737-9357 Fax: (541) 737-4600 http://oregonstate.edu/~yokochia -Original Message- *From:* Kurt Leinenweber [mailto:ku...@asu.edu] *Sent:* Thursday, January 08, 2009 6:09 PM *To:* Rietveld_l@ill.fr *Subject:* error in peak positions that is linear in theta Dear Rietvelders, (I hope this list is appropriate for this question). I am trying to set up a new D8 diffractometer from Bruker, and have it set up with a Vario monochromator focusing on a sample in a capillary. Of course I hope to do Rietveld refinement on the samples eventually. But there is an error in two theta of the peak positions on all samples, and the error is linear in two theta. At 40 degrees the error (measured minus expected) is about 0.020 degrees, at 80 degrees the error is about 0.040 degrees, etcetera. Has anyone ever seen anything like this and do you know where it could come from? Thank you very much, - Kurt * Kurt Leinenweber Dept. of Chemistry and Biochemistry Arizona State University Tempe, AZ 85287-1604 phone (480)-965-8853 fax (480)-965-2747 ***
RE: error in peak positions that is linear in theta
Kurt, It looks like incorrect step size (difference between actual step size and one that is written in the file) or incorrect distance to the detector. The later may incorrect step size if detector is PSD. I have similar situation with much smaller difference in peak position but the shift (difference between actual and written step size) varies from measurement to measurement. Bruker is working on this but so far no solution/cause is known. Your case may be simpler if the difference is constant. Perhaps calibration of detector or its distance to the sample is needed. Best, Peter Zavalij X-ray Crystallographic Center University of Maryland College Park, MD Office: (301)405-1861 Lab: (301)405-3230 Fax: (301)314-9121 From: Kurt Leinenweber [mailto:ku...@asu.edu] Sent: Thursday, January 08, 2009 6:09 PM To: Rietveld_l@ill.fr Subject: error in peak positions that is linear in theta Dear Rietvelders, (I hope this list is appropriate for this question). I am trying to set up a new D8 diffractometer from Bruker, and have it set up with a Vario monochromator focusing on a sample in a capillary. Of course I hope to do Rietveld refinement on the samples eventually. But there is an error in two theta of the peak positions on all samples, and the error is linear in two theta. At 40 degrees the error (measured minus expected) is about 0.020 degrees, at 80 degrees the error is about 0.040 degrees, etcetera. Has anyone ever seen anything like this and do you know where it could come from? Thank you very much, - Kurt * Kurt Leinenweber Dept. of Chemistry and Biochemistry Arizona State University Tempe, AZ 85287-1604 phone (480)-965-8853 fax (480)-965-2747 ***
Re: error in peak positions that is linear in theta
Dear Kurt, It seems that the problem is in wrong sample-to-detector distance which results in the nearly linear angular dependence of the peak displacement. Regards, Leonid * Leonid A. Solovyov Institute of Chemistry and Chemical Technology 660049, K. Marx 42, Krasnoyarsk, Russia www.icct.ru/eng/content/persons/Sol_LA www.geocities.com/l_solovyov * --- On Thu, 1/8/09, Kurt Leinenweber ku...@asu.edu wrote: (I hope this list is appropriate for this question). I am trying to set up a new D8 diffractometer from Bruker, and have it set up with a Vario monochromator focusing on a sample in a capillary. Of course I hope to do Rietveld refinement on the samples eventually. But there is an error in two theta of the peak positions on all samples, and the error is linear in two theta. At 40 degrees the error (measured minus expected) is about 0.020 degrees, at 80 degrees the error is about 0.040 degrees, etcetera. Has anyone ever seen anything like this and do you know where it could come from? Thank you very much, - Kurt * Kurt Leinenweber Dept. of Chemistry and Biochemistry Arizona State University Tempe, AZ 85287-1604 phone (480)-965-8853 fax (480)-965-2747 ***
