[mcstas-users] About Silicon analyzer

[Erik Bergbäck Knudsen]

Dear Jesus,

I believe there could be something wrong with your definition of unit
cell vectors for Si. For instance, in your case, the angle between a and
b is 60 deg. which does not fit with the cubic structure that Si
generally exhibits. I'm not sure about the lengths of the unit cell
vectors either: |a| = 3.84 Å does not seem right.

To simply exclude the .lau file from the crystal definition will have
the effect of completely disregarding coherent scattering in the
simulation - you will therefore only see the contribution from
incoherent scattering, which is probably not what you intended.

To tell you exactly what the _right_ way to use Single_crystal as an
analyzer is very difficult, as there are many ways. We'd be happy to
help you find the right way for you, but to do so, we will need more
details on what it is you're actually trying to do. If you attach a copy
of the .instr file and whatever extra files that are needed to run your
simulation we may be able to help you accomplish your task.

kind regards and happy simulating
Erik B Knudsen

On 09/08/2014 05:13 PM, Jesús P. de Vicente wrote:
> Dear McStas team,
> 
> I am trying to perform simulations with a silicon analyzer.
> 
> I use the *Single_crystal* component. For graphite material everything
> works fine:
> // *PG* *************************
>   mosaic = 48, 
>   reflections = "C_graphite.lau", barns=0,
>   ax=0,      ay=2.14,   az=-1.24,
>   bx = 0,    by = 0,    bz =  2.47,
>   cx = 6.71, cy = 0,    cz =  0,
>   sigma_abs = 0.014, sigma_inc = 0.004,
> //**************************
> 
> But I do not get to work with silicon material. I use the following syntax:
> // *Si* *************************
>  reflections = "Si.lau", barns=0,
>  mosaic = 0.1, delta_d_d = 3.10e-4,
>  sigma_abs = 0.171, sigma_inc = 0.004,
>  ax = 2.715, ay = 2.715, az = 0.0,
>  bx = 0.0, by = 2.715, bz = 2.715,
>  cx = 2.715, cy = 0.0, cz = 2.715,
> //**************************
> 
> I built a Si.lau file from the a Si.cif file using Crystallographica
> software.
> I have tried lot of configurations, but I got always lot of peaks with
> the backscatteing configuration. I tried also the simulation without the
> reflection *.lau file but I have no peaks.
> 
> Do you know what would be the right way to perform a simulation with a
> silicon analyzer using the Single_crystal component?
> 
> Thank you very much for your help.
> Kind regards.
> 
> 
> 
> *Jesús P. de Vicente.-*
> 
> 
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-- 
Erik Bergbäck Knudsen, Research Engineer         | DTU | morituri
NEXMAP, DTU Fysik, DK-2800 Kgs. Lyngby, Denmark  |<>-<>|    te
phone: (+45) 2132 3151, mobile: (+45) 3123 6184  |<>-<>| salutant