Re: how to find out POLARISATION Factor
How about even lower angles? From: Larry Finger [mailto:[EMAIL PROTECTED] Sent: Tue 5/30/2006 4:25 PM To: rietveld_l@ill.fr AlanCoelho wrote: > I would like to conclude that to be critical of a method such as the > convolution approach to describing instrument line profiles it would serve > authors best to first investigate the approach rather than to be critical of > it without substance. > Amen! I'm really impressed with how well the convolution method has done. Without any way to test it, I've always had to accept the ray-tracers argument that they did better. I all knew is that convolution did well enough. You have shown that it makes no real difference. Would it be possible for you to generate the data points for the same set of parameters with peaks at 5 and 10 degrees? That way the asymmetry will be really pronounced and the convolution method will be even more stressed. I don't expect it to make any difference, but I'd like to see it on the screen. Thanks, Larry
Re: how to find out POLARISATION Factor
AlanCoelho wrote: I would like to conclude that to be critical of a method such as the convolution approach to describing instrument line profiles it would serve authors best to first investigate the approach rather than to be critical of it without substance. Amen! I'm really impressed with how well the convolution method has done. Without any way to test it, I've always had to accept the ray-tracers argument that they did better. I all knew is that convolution did well enough. You have shown that it makes no real difference. Would it be possible for you to generate the data points for the same set of parameters with peaks at 5 and 10 degrees? That way the asymmetry will be really pronounced and the convolution method will be even more stressed. I don't expect it to make any difference, but I'd like to see it on the screen. Thanks, Larry
How to prepare intensity and hkl files needed by SHELXTL-97
Use "R" option in REFLIST R.B. Von Dreele IPNS Division Argonne National Laboratory Argonne, IL 60439-4814 -Original Message- From: Dr. Yi-Ping Tong [mailto:[EMAIL PROTECTED] Sent: Tuesday, May 30, 2006 9:55 AM To: Rietveld BBS software? Dear all Does anybody could tell me how GSAS can extract intensity and hkl valuesneeded by SHELXTL-97 software for structure determination ? Any suggestions or comments are welcome. Thanks in advance. Best wishes Dr. Y. P. Tong China
Re: how to find Polarization
Will Bisson wrote: Dear Larry, When you removed the soller slits leading to increased the axial divergence, which profile function is appropriate to model this, especially at low angle where the asymmetry is very stark? I used GSAS profile type 3, which incorporates the Finger, Cox and Jephcoat calculations. The method accounts for the increasing asymmetry at low angles as well as the intensity correction required because the low-angle peaks intercept a bigger piece of the Debye-Scherrer rings. Larry
How to prepare intensity and hkl files needed by SHELXTL-97 software?
Dear all Does anybody could tell me how GSAS can extract intensity and hkl valuesneeded by SHELXTL-97 software for structure determination ? Any suggestions or comments are welcome. Thanks in advance. Best wishes Dr. Y. P. Tong China
Re: how to find Polarization
Dear Larry, When you removed the soller slits leading to increased the axial divergence, which profile function is appropriate to model this, especially at low angle where the asymmetry is very stark? Kind regards William On 30 May 2006, at 16:01, Larry Finger wrote: [EMAIL PROTECTED] wrote: Dear All, if I well understood JFC correction is perfect in case of parallel incident beam; so, in case of conventional Bragg-Brentano diffractometer, shouldn't it work well only in case of use of Goebel Mirrors, that get incident beam exactly parallel? And is it true that using Goebel Mirrors and sample in capillary (Debye-Scherrer) gets intensity values more realistic than on a conventional Bragg-Brentano geometry? Thanks in advance, marco Not really. The FCJ correction (note the authorship please) was derived for the parallel incident beam case, but it works for divergent optics. The main difference is that for the parallel beam case, one can measure the slit sizes perpendicular to the plane formed by the incident and diffracted beams, directly calculate the values for S/L and H/L, and get values very close to the "best-fit" results. For divergent beam optics, the "effective" width is greater than the apparent width. As discussed earlier in this list, in the divergent beam case, a set of 0.02 (radian) slits will yield refined values of 0.027 for S/L and H/L, not 0.02 as predicted from the geometry. In the extreme case, I removed the Soller slits on my conventional B-B diffractometer, and could still fit the resulting profiles, which were greatly affected by axial divergence. As I recall, S/L and H/L were on the order of 0.2! BTW, the intensities were increased by roughly a factor of 10. I had to cut the tube power to avoid saturating the detector. Putting your sample in a capillary avoids a lot of sample problems that occur with a flat plate; however I'm not sure that I would make the blanket statement that you do. That topic should be addressed by someone with experience with mirrors. Larry -- William Bisson Davy Faraday Research Laboratory The Royal Institution of Great Britain 21 Albemarle Street London W1S 4BS Tel: +44 (0)20 7670 2977 (Direct) Tel: +44 (0)20 7409 2992 (Switchboard) Fax +44 (0)20 7670 2958 Http://www.ri.ac.uk/DFRL/ The RI is a registered charity (number 227938)
Re: how to find Polarization
[EMAIL PROTECTED] wrote: Dear All, if I well understood JFC correction is perfect in case of parallel incident beam; so, in case of conventional Bragg-Brentano diffractometer, shouldn't it work well only in case of use of Goebel Mirrors, that get incident beam exactly parallel? And is it true that using Goebel Mirrors and sample in capillary (Debye-Scherrer) gets intensity values more realistic than on a conventional Bragg-Brentano geometry? Thanks in advance, marco Not really. The FCJ correction (note the authorship please) was derived for the parallel incident beam case, but it works for divergent optics. The main difference is that for the parallel beam case, one can measure the slit sizes perpendicular to the plane formed by the incident and diffracted beams, directly calculate the values for S/L and H/L, and get values very close to the "best-fit" results. For divergent beam optics, the "effective" width is greater than the apparent width. As discussed earlier in this list, in the divergent beam case, a set of 0.02 (radian) slits will yield refined values of 0.027 for S/L and H/L, not 0.02 as predicted from the geometry. In the extreme case, I removed the Soller slits on my conventional B-B diffractometer, and could still fit the resulting profiles, which were greatly affected by axial divergence. As I recall, S/L and H/L were on the order of 0.2! BTW, the intensities were increased by roughly a factor of 10. I had to cut the tube power to avoid saturating the detector. Putting your sample in a capillary avoids a lot of sample problems that occur with a flat plate; however I'm not sure that I would make the blanket statement that you do. That topic should be addressed by someone with experience with mirrors. Larry
Re: how to find Polarization
Dear All, if I well understood JFC correction is perfect in case of parallel incident beam; so, in case of conventional Bragg-Brentano diffractometer, shouldn't it work well only in case of use of Goebel Mirrors, that get incident beam exactly parallel? And is it true that using Goebel Mirrors and sample in capillary (Debye-Scherrer) gets intensity values more realistic than on a conventional Bragg-Brentano geometry? Thanks in advance, marco Marco Sommariva -- Marco Sommariva Department of Materials Science University Milano-Bicocca Via R. Cozzi 53, 20125 Milano (ITALY) mail: [EMAIL PROTECTED] phone: 0039.02.64.48.51.41 fax: 0039.02.64.48.54.00 --