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From: "Jie Shao" [jieshao@hotmail.com] To: Rietveld_l@ill.fr Subject: Absorption Date: Fri, 02 Nov 2001 13:49:29 -0800 I'm using GSAS to process my XRD data (capillary geometry), and I'd like to know how to correct the absorption effect (My sample contains heavy elements). I measured the packing density of the sample capillary, and I can calculate the mu based on it and the wavelength. However, according to the GSAS manual, I need to input A = mu*R/lamda. What is R? What are the units I should use for mu (cm-1?), R, and lamda (A?)? Thanks for your help.

Date: Mon, 05 Nov 2001 08:02:08 -0700 To: rietveld_l@ill.fr From: vondreele@lanl.gov (Bob Von Dreele) Subject: Re: Absorption Dear Jie (and anyone else), According to the GSAS Manual (pp 138-140) the cylindrical absorption function requires mu*R/lambda. mu is the linear absorption coefficient for the sample in units that are commensurate with the radius of the cylinder (R). Usually one uses mu in cm-1 and R in cm. mu should be corrected for the packing efficiency which is typically 50%. The divide by lambda is a kluge to allow use of the absorption function for neutron TOF. Please note that the cylindrical absorption function is no good if mu*R exceeds ~30. Bob Von Dreele

Date: Mon, 05 Nov 2001 08:02:08 -0700 To: rietveld_l@ill.fr From: vondreele@lanl.gov (Bob Von Dreele) Subject: Re: Absorption Dear Jie (and anyone else), According to the GSAS Manual (pp 138-140) the cylindrical absorption function requires mu*R/lambda. mu is the linear absorption coefficient for the sample in units that are commensurate with the radius of the cylinder (R). Usually one uses mu in cm-1 and R in cm. mu should be corrected for the packing efficiency which is typically 50%. The divide by lambda is a kluge to allow use of the absorption function for neutron TOF. Please note that the cylindrical absorption function is no good if mu*R exceeds ~30. Bob Von Dreele

Date: Mon, 05 Nov 2001 17:24:27 +0000 To: rietveld_l@ill.fr From: Lachlan Cranswick [l.m.d.cranswick@dl.ac.uk] Subject: Re: Absorption Reply-To: rietveld_l@ill.fr >According to the GSAS Manual (pp 138-140) the cylindrical absorption >function requires mu*R/lambda. mu is the linear absorption coefficient for >the sample in units that are commensurate with the radius of the cylinder >(R). Usually one uses mu in cm-1 and R in cm. mu should be corrected for >the packing efficiency which is typically 50%. The divide by lambda is a >kluge to allow use of the absorption function for neutron TOF. Please note >that the cylindrical absorption function is no good if mu*R exceeds ~30. For handling high mu*R materials, one method that is applied in the CSIRO Minerals XRD lab is to dilute the sample with Industrial Diamond powder. This does not give too many extra peaks, it keeps the background the same and the Diamond peaks can be used as an internal position standard. Lachlan. ----------------------- Lachlan M. D. Cranswick Collaborative Computational Project No 14 (CCP14) for Single Crystal and Powder Diffraction Birkbeck University of London and Daresbury Laboratory Postal Address: CCP14 - School of Crystallography, Birkbeck College, Malet Street, Bloomsbury, WC1E 7HX, London, UK Tel: (+44) 020 7631 6849 Fax: (+44) 020 7631 6803 E-mail: l.m.d.cranswick@dl.ac.uk WWW: http://www.ccp14.ac.uk/

From: "Yokochi, Alexandre" [alex.yokochi@orst.edu] To: "'rietveld_l@ill.fr'" [rietveld_l@ill.fr] Subject: RE: Absorption Date: Mon, 5 Nov 2001 10:31:59 -0800 Hi, As a further comment on the absorption correction, for a cylindrical shaped sample and for angle dispersive instruments (i.e., not TOF, with which I am not too familiar), the correction for absorption and extinction can be handled separately from the structure refinement program, as it is handled by a geometrical construct and (at least in my oppinion) it should never have refinable parameters. I think that there is a program called something like CORRECT that will do this. For my lab X-rays, the diamond powder thing works very well. LiF also works well, but gives lots more lines. However, LiF is a lot cheaper, and usually readily available. AlexY Dr. Alexandre F. T. Yokochi Assistant Professor (Senior Research) Director, X-ray Crystallographic Facilities Department of Chemistry Oregon State University Corvallis, OR 97331-4003 Ph# (541) 737-6724 Email: alex.yokochi@orst.edu Fax# (541) 737-2062 Web Page: www.chem.orst.edu/yokochi