[mcstas-users] Attenuation in powder sample

[John.Brokx]

Dear all


I am using McStas to run simulations(scans) of a powder sample for the ENGINX instrument (ISIS RAL).

The powder sample is made of an Aluminium hull filled with iron. The density of the real sample is 41 % of

solid iron and has a linear attenuation coefficient of 0.45 /cm. I am using the packing factor as explained in the McStas component manual(section on PowderN component) to reflect this.

I ran several simulations with different values of the packing factor. I started initially with a packing factor of 0.41 but it appeared that I needed a packing factor of 0.82 to get a good match with the  real measurements done on ENGINX. I suspect that the factor 2 comes from the number of atoms in the unit cell but I am not entirely sure. I am interested to understand how the packing factor relates to the attenuation and density and if there are other ways in McStas to adjust the attenuation.



Thanks

John Brokx

Open University UK
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