[neutron-mc] Re: detector output files

Emmanuel Farhi farhi at ill.fr
Thu Jul 31 12:26:47 CEST 2003

Hello Timur,

The 'N' data has no physical sense. It is a number of simulation events
for a given data bin. You basically should not use that data, except if
you wish to study the simulation statistics and efficiency (see Manual, p
In McStas, a simulation event may be regarded as a pack of neutrons,
containing 'p' particules. When this event propagates, its 'filling'
decreases, and the total weight of the pack is the intensity 'I' when
stored in monitor bins, even if the event is still there (and counts for
'1' in 'N').

I also remember that some e-mails about this are in the neutron-mc
archive. Browse it to find comments from Kristian Nielsen, probably in

Good luck with Mcstas, Emmanuel.

Timur Elzhov wrote:

> oops, the messaage has run away ... :-)
> so, I use Source_Maxwell source to generate neutrons, and detect
> them with 1D detector. And, I couldn't understand the imeaning of `N'
> colon from the detector out file. `I' shows the actual distribution -
> that's what I want. I believe that detector catches less neutrons for
> one bin and more for another bin, in accordance for the maxwell
> distribution.  But I found in the manual:
>   One-dimentional histogran detectors: ...
>       Each line contains a number identifying the bin followed by three
>       numbers: the simulated intensity, an estimate of the SE, and the
>       number of neutron events for this bin.
> And the last, "number of neutron events for the bin", is _constant_ for
> the maxwell source distribution (I guess for any other distribution
> either).
> Could anybody explain me what the `N' colon means? At first time
> I pointed that this colon looked like transmission function for
> netron guides. But then I calculated I(after_guide)/I(before_guide)
> and found result _quantatively_ different from N(after_guide).
> Thank you!
> --
> WBR,
> Timur.
> _______________________________________________
> neutron-mc mailing list
> neutron-mc at neutron.risoe.dk
> http://neutron.risoe.dk/mailman/listinfo/neutron-mc

What's up Doc ?
Emmanuel FARHI, http://www.ill.fr/tas/people/Farhi.html   \|/ ____ \|/
CS-Group ILL4/156, Institut Laue-Langevin (ILL) Grenoble  ~@-/ oO \-@~
6 rue J. Horowitz, BP 156, 38042 Grenoble Cedex 9,France  /_( \__/ )_\
Work :Tel (33/0) 4 76 20 71 35. Fax (33/0) 4 76 20 76 48     \__U_/

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