[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
