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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