[mcstas-users] Help with Single_crystal

[Agustin Beceyro]

Hello to everyone!

I'm writing this email because I'm finding some trouble while using the
Single_crystal component and comparing it with the Monochromator_curved
component.

My input is extremely simple: a source, a Ge monochromator, and a PSD
monitor. The monochromator has vertical focusing, so it is formed by 7
crystals (for Monochromator_curved Nv=7, for Single_crystal I've grouped 7
components).

I've been playing around a little bit with this configuration, change the
distance source-monochromator, monochromator-detector, the monochromator
take-off angle, add collimators, even changed the number of crystals used.
For each configuration, I made a scan of Rv (vertical focusing radio).
While plotting the Rv vs. normalized intensity I get the same behavior in
all cases, and maximum intensity is achieved with the theoretically
calculated value of Rv.

My problem arose when evaluating the PSD intensity. With Single_crystal I
get between 0.22 and 0.24 of the intensity I get with the other component
(in every single case). I believed it was a reflectivity issue, but
changing the take-off angle affects lambda and the reflectivity. Besides, I
compared these values with different bibliography and it seems OK.

Besides, I've done another test with a geometry very similar to Stress-Spec
and compared it to some published data. With Monochromator_curved I
obtained about 30% more intensity (but I don't ha the exact geometry or
source), with Single_crystal I obtained 70% less intensity. Still, the
ratio between both cases remains 0.23.

I'm sure I'm missing something, but I can't figure out what and I can't
find anything related to the validation of the component. Someone, any
clues?

With best regards,


Ing. Agustín Beceyro Ferrán
Departamento de Física de Neutrones
Centro Atómico Bariloche - CNEA
San Carlos de Bariloche
Rio Negro, Argentina
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