[mcstas-users] intercomparison between McStas and SIMRES

Peter Willendrup pkwi at risoe.dtu.dk
Wed Aug 19 21:02:44 CEST 2009

Hello again,

You are absolutely right Jan, attached is a version of the graph  
parametrized by \delta\theta instead. The overall shape agrees quite  
well - possibly there is a sign difference in \delta\theta, the slight  
asymmetry in the side peaks seems opposite in the two graphs.

Now for comparing intensity:

The maximum reflectivity of the monochromator has been set to 0.265 in  
Tom's instrumentfile, I would think this is a fairly low value?

And in regard to the sample parameters, we tend not to trust the  
listed F-squared in .laz input files too much. ( .lau ones can be  
generated in Crystallographica and are usually in better agreement  
with reality)

Consequently,  I think that given the circumstances the agreement is  
quite fair.



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On 19/08/2009, at 17.46, Jan Saroun wrote:

> Hello Tom and Peter,
> I think the problem is the theta-scale. I suppose DTT on the Peter's  
> result is the full scattering angle, while the data shown by Tom are  
> on Bragg angle (=DTT/2) scale. If you correct for this, the two  
> profiles are very close. Also the intensity scale is not MUCH  
> different, we should check first the input data for the  
> monochromator and sample in order to resolve this. I attach the  
> curves simulated by SIMRES with the two methods I have mentioned  
> earlier (theta-scan and resolution function).
> Regards,
> Jan
> Peter Willendrup wrote:
>> Hello Tom, Jan,
>> I agree with Jan, you need to perform a scan in 2\theta. I have  
>> modified Tom's instrument slightly - optimizing it slightly - and  
>> performed the proposed scan. Please find attached both the  
>> instrumentfile and the resulting peak profile. It now looks much  
>> more like your result from SIMRES, but a bit more broad.
>> A closer study of SIMRES parameters in comparison to the McStas  
>> component parms will very likely resolve this discrepancy. As Jan  
>> also mentions, intensity agreement is a bit more complicated. :)
>> Best regards,
>> Peter Willendrup
> -- 
> -----------------------------------------
> Dr Jan Saroun Nuclear Physics Institute
> Academy of Sciences of the Czech Republic
> 25068 Rez near Prague
> phone: 420-2-66173140 phone/fax: 420-2-20940141
> mailto:saroun at ujf.cas.cz
> <tom_simres.png>

Peter Willendrup - Development engineer

Materials Research Division
Frederiksborgvej 399
DK-4000 Roskilde

Tlf.: (+45) 4677 5862
Mobil.: (+45) 2125 4612
Fax.: (+45) 4766 5758
Email: pkwi at risoe.dtu.dk

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