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 --
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 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 x-tad-smaller--/x-tad-smaller x-tad-smallerWilliam 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 /x-tad-smallerx-tad-smallerHttp://www.ri.ac.uk/DFRL//x-tad-smallerx-tad-smaller The RI is a registered charity (number 227938) /x-tad-smaller
