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McStas Sqw component: use 'standard' Bose factor weighting #300

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farhi opened this Issue Jul 7, 2016 · 4 comments

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farhi commented Jul 7, 2016

See http://ifit.mccode.org/Treatment.html#mozTocId906474

Should use 'standard' or 'Frommhold' Q = 2./(1+exp(-hw/kT))

This should fix issues when normalizing classical Sqw data, which result in a very large norm with the exp(hw/2kT) weighting, and most probably produces wrong results.

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willend commented May 17, 2017

Related user report from Ketty Beauvois, CNRS

Dear Ken,

When we met at ECNS last year in Spain, we discussed together with
 Björn Fåk in front of my poster "The excitations in superfluid 4He". 
For the data treatment,  I performed multiple scattering calculations 
using McStas. I found a problem that I describe in the report 
"McStas.pdf" (attached). I tested also two other programs for the 
multiple scattering calculations. One is MScat (written by John Copley)
and the other is written by Javier Dawidowski. I sent him a report called
 "multiple_scattering.pdf" (also attached), which compares the results 
from the three Monte Carlo programs. I would like to know if you have 
any idea where the problems could come from in McStas. I would be 
happy to discuss or respond to any questions.

Best regards,

Ketty Beauvois

McStas.pdf
multiple_scattering.pdf

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farhi commented Nov 26, 2018

In fact, Isotropic_Sqw uses 'Schofield' / 'Boltzmann' Bose factor. This is not adapted when temperature is lower than the excitation energies. This is mostly the case for liquid 4He and other cryogenic liquids.

I will try a fix in relation with #196

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farhi commented Nov 27, 2018

This is duplicate of #196.

@farhi farhi closed this Nov 27, 2018

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farhi commented Nov 28, 2018

Done with commit 5b026b3
see #196.

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