[mcstas-users] Reflectivity and transmission files of Ge crystal

[Peter Kjær Willendrup]

Dear Saed,


On 9 May 2018, at 11:30 , 새드하셈 <saed at kaeri.re.kr<mailto:saed at kaeri.re.kr>> wrote:

Actually I have one question and one inquiry:

Q: I'm trying to simulate the HANARO_HRPD by using McStas software.  But after I inserted all required components and their parameters as designed/as they are on ground now,  I found a kind of difference between the McStas_flux magnitude and the Real_flux magnitude both at sample position in (n/cm2.s) !! and the difference is high enough to say there is something wrong I can't figure it ! {Real_flux is around (1.3e6) n/cm2.s where McStas_flux is (1.9e5) n/cm2.s.} although I get almost exact matching result at monochromator position.

It is always easier to comment or correct if there is acces to the instrument file, as well as other necessary data.

I would therefor encourage you to send the instrument file, plus descriptive material about your beamline in response to this email.


And my concerns also increased when some experts (2 experts to be honest) told me that McStas doesn't show the flux magnitude as calculated or expected !! So is this True ?!  and if yes, what is the accepted difference between McStas and Real, i.e. the criteria or error margin to consider?

I my experience McStas is reasonably reliable, and to a large extent simulates exactly what one parametrises. This of course means that if the source emission or certain material- or geometrical data are put in with values that are off, the simulation will naturally also be off. :-)

A rule of thumb is that with modest effort, one can arrive within 10% of what one would measure. Better agreement than that typically requires lots of more thinking, coding, simulating and benchmarking.

But again, without access to what you are trying to simulate and how, it is hard to judge what is going on. We are "flying blind".


Inquiry: I tried to get the Reflectivity files of Ge crystal  to define a curved Monochromator with four wavelengths (1.54, 1.834, 1.866, 2.224 A), but unfortunately I couldn't find any source that provide a tabulated data of the wavelength and the absolute Ge crystal reflectivity. So is there anyone who could help me in this also?

I must admit I am not much of a monochromator-expert, but I would try looking among papers by Freund et. al from the 1970’s and 80’s.


Best regards,

Peter Willendrup

Peter Kjær Willendrup
Forskningsingeniør, Speciakonsulent
Næstformand for DTU Fysik LSU



DTU Physics

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Technical University of Denmark



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