[mcstas-users] Diffraction Pattern of Si

Linda Udby udby at nbi.dk
Wed Nov 22 15:12:52 CET 2017

Hi Saed,

you are right the 220 reflection has zero intensity in the Si.laz file 
as you can see here

I believe that is not correct for the diamond structure of Si (F -d 3m)

S_Si(hkl)=S_fcc(hkl)[1+exp(i pi /2)(h+k+l)]
where S_fcc(hkl)=4b_Si for h,k,l all odd or even, else S_fcc(hkl)=0


S_Si(220) = 2 * S_fcc(hkl)= 8 b_Si

( but S_Si(hkl) = 0 if  [h+k+l=2(2n+1)]  )

A solution would be to generate your own reflection list (h,k,l, 
Intensity) from e.g. crystallografica and input that as datafile to  the 
component where you have used Si.laz before. When you have generated a 
better reflection list for Si I'm sure the McStas developers would be 
happy if you contribute it to the next McStas distro :)

Best wishes

On 11/22/2017 09:21 AM, 새드하셈 wrote:
> Hello everyone,
> Here is Mr. Saed Almomani from KAERI, I'm working on conceptual design 
> of HRPD for the Jordan Research & Training Reactor JRTR.  I'm using 
> McStas software to test and verify my design, and when I used 
> the Si.laz sample in my code I found that some of reflection planes 
> are not shown in the diffraction pattern such as (220) !!  then I 
> tried to use D2B HRPD code (built-in McStas) to test the Si.laz sample 
> and the problem was the same " the 220 reflection plane was not shown" 
> !! then I tried to use the Al.laz sample and I got a perfect 
> diffraction pattern !
> So what is the problem and why is that ? is there any error in the 
> (Si.laz) predefined sample of McStas ? and what is the best way to 
> solve this problem?
> Thank you in advance
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Dr. Linda Udby
Associate Professor
X-ray and Neutron Science
Niels Bohr Institute
University of Copenhagen
tel: +45 23 83 98 77
webpage: www.e-neutrons.org

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