[mcstas-users] divergence monitor output

Zhang, SY (Shu Yan) shu-yan.zhang at stfc.ac.uk
Mon Jul 6 13:56:39 CEST 2009

Dear Emmanuel


Thank you very much for the information. Regarding the divergence output
dX and dY, are they the full width half maximum or the c value in the
Gaussian function?




Many thanks for your reply!!



-----Original Message-----
From: Emmanuel FARHI [mailto:farhi at ill.fr] 
Sent: 03 July 2009 20:23
To: McStas users list at mcstas.org
Subject: Re: [mcstas-users] divergence monitor output


Hello Shu,


Any divergence monitor such as the Divergence_monitor() or the

Monitor_nD(options="hdiv vdiv, all auto") will indeed produce a  




Then the output files have lines:

  value: I I_err N

  statistics: X0 dX Y0 dY


I, I_err and N: are the values of the intensity (usually integrated  


the error bar on this value, and the number of statistical MC events

recorded on the detector (which is not the flux, but a non physical  


count, only for computational purpose).


X0 dX Y0 dY: are the center (mean value, 1st moment) and second moment

(gaussian width) of the distributions. In your case, dX and dY will give

you a gaussian width of the H and V divergence. X0 and Y0 should in

principle be around zero if the monitor is well oriented.

just do

>> eval(mc_divmon_dat.statistics); [ dX dY ]





> Dear all


> I have question about the results from the Divergence_monitor  

> Component.

> I want to find out the beam divergence. Is this the right monitor to

> use? If it is, which value in the output file shall I use as the  

> maximum

> divergence? What do these values X0, dX, Y0 and dY from

> "mc_divmon_dat.statistics" mean? What are the meaning for the values

> from "mc_divmon_dat.values"?


> Best regards,

> Shu




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FARHI Emmanuel <farhi at ill.fr>

Groupe DS/CS, ILL4/156, Tel 04 76 20 71 35

ILL, Grenoble


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