[neutron-mc] Re: comparing time and lambda monitors

[Emmanuel Farhi]

Hy Dickon,

As you know, McStas components (and monitors) are written by many contributors.
Thus the way data is sorted and stored depends on each monitor. Anyway, most of
them behave the same way.
I think the difference comes from the source, or the way the source is emitted.
If you look at 'mcdoc Source_gen' you will see in the doc that the flux is
dPhi/dLambda (n/s/AA) over the whole 4Pi sphere, but focused to the target area
(guide input), and per source emission area (1/cm^2) .
This is the about same in 'Source_Maxwell' sources. There is your 1/Lambda
factor.

Emmanuel.

"Champion, JDM (Dickon)" wrote:

> PS- i'm not ruling out the possibility that the input is junk.....
>
> Dr Dickon Champion
> ISIS Facility
> R3 Room 1-49
> Rutherford Appleton Laboratory
> Chilton
> OX11 0QX
>
> Tel : 01235 446043 (Office)
>       07939 084159 (Mobile)
>
> Fax : 01235 445720
>
> > -----Original Message-----
> > From: Champion, JDM (Dickon)
> > Sent: 15 March 2004 14:45
> > To: 'Geza'; 'klaus'; 'willendrup'; 'Kim Lefmann'; 'Emmanuel Farhi'
> > Subject: RE: comparing time and lambda monitors
> >
> >
> > i attach the data files for the two pictures
> >
> >
> >
> > Dr Dickon Champion
> > ISIS Facility
> > R3 Room 1-49
> > Rutherford Appleton Laboratory
> > Chilton
> > OX11 0QX
> >
> > Tel : 01235 446043 (Office)
> >       07939 084159 (Mobile)
> >
> > Fax : 01235 445720
> >
> >
> > > -----Original Message-----
> > > From: Champion, JDM (Dickon)
> > > Sent: 15 March 2004 14:19
> > > To: Geza; klaus; willendrup; Kim Lefmann; Emmanuel Farhi
> > > Subject: comparing time and lambda monitors
> > >
> > >
> > > hi,
> > >
> > > in my neverending simulation of HET i came across an odd
> > > conundrum last week, in an effort to resolve the
> > > discrepancies in the flux.... it didn't solve anything, it
> > > only created more problems in my head.
> > >
> > > if i simulate a large range of energy, for example 0.4-2.9 A,
> > > and measure the beam 1 cm from the moderator face with two
> > > identically configured lambda monitors in vitess and mcstas
> > > (there is no point in attaching instrument since they are so
> > > basic). even with the slight differences in sampling the
> > > beam, you would expect there to be a general agreement
> > > between the monitor output. these two datasets are shown in
> > > the mcstas.jpg and vitess.jpg files attached. as you can see
> > > the distributions are fundamentally different.
> > >
> > > however stuart and i were playing around with the figures and
> > > determined that you can get the vitess plot to agree with the
> > > mcstas if you divide the intensity column entries by the
> > > lambda column, ie. a 1/lambda correction. i was looking
> > > through the source of the modules and it seems to be a simple
> > > binning operation.
> > >
> > > as far as i am aware both modules are supposed to have the y
> > > axis in terms of neutrons/second?? am I missing something in
> > > the small print somewhere?? are the software packages
> > > measuring something different? and if so, why, and why isn't
> > > there anything written about it???
> > >
> > > there is also quite a difference in the distribution given by
> > > identically configures time monitors as well, which isn't
> > > evident for a small range in energy, but by  dividing through
> > > by the time, an improved agreement is again observed.
> > >
> > >
> > > any ideas????? thank you for any light you can shed in this
> > matter....
> > >
> > > dickon
> > >
> > > Dr Dickon Champion
> > > ISIS Facility
> > > R3 Room 1-49
> > > Rutherford Appleton Laboratory
> > > Chilton
> > > OX11 0QX
> > >
> > > Tel : 01235 446043 (Office)
> > >       07939 084159 (Mobile)
> > >
> > > Fax : 01235 445720
> > >
> >

--
What's up Doc ?
--------------------------------------------
Emmanuel FARHI, http://www.ill.fr/Computing/people/Farhi  \|/ ____ \|/
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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