After having purchased the set of 0.02 soller slits in Dec. 03 I have
done some comparison tests on the (111) silicon peak under identical
conditions except for the change of the primary and secondary sollers:
background B peak height PH
0.02 95 8580
0.04 320 18900
negliable change on the FWHM
so not an intensity drop with a factor of 25, neither 4, but only
slightly larger than 2.
How do I define signal/background ratio? There is not much scientific in
it, it serves only to compare qualitatively these kind of 'optical'
elements; it should be something like (PH-B)/B or more generally Bragg
scattering intensity to non-Bragg-scattering intensity.
Arie
Dear Mike,
Normally, changing sollers must not influence the signal/background
ratio. Wider sollers, however, make the primary beam wider and if the
sample diameter is small then a parasitic scattering from the sample
holder edges may appear.
I am really surprised that moving from 0.04 Soller slits to 0.02 you
got 25 times intensity reduction. When I change the primary soller from
0.04 to 0.02 the intensity drops ~2 times, so if you changed both the
primary and the secondary sollers the intensity should decrease ~4
times, but not 25 times.
Leonid Solovyov
How do you define signal to noise in powder diffraction? I have seen
this term used several times, but I have not found a definition so
far
with regard to powder diffraction per se.
I have just done two runs on a Panalytical one with 0.04 soller slits
and one with 0.02 (both with a CuKa1 premonochromator) both for
about 9
hours. The strongest peak for the 0.02 case is 2700 counts, half
width
0.08 degrees and a background of 25 counts. The same peak with the
0.04
slits has 70000 counts, half width 0.11 degrees and a background of
700 counts.
Mike Glazer
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A. van der Lee
Institut Européen des Membranes
CNRS - UMR 5635
Université de Montpellier II - Case Courrier 047
Place E. Bataillon
34095 MONTPELLIER Cedex 5 - FRANCE
Tel : 33 (0) 4 67 14 91 35
Fax : 33 (0) 4 67 14 91 19
Website X-ray scattering facility ICG/IEM:
http://www.iemm.univ-montp2.fr/xrayweb/main_uk.html
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