From: Markus Brugger (Markus.Brugger@cern.ch)
Date: Fri Feb 02 2007 - 15:41:43 CET
Hi Sunil,
the input file helped to understand what you observe and as far as we
understand this seems to be consistent:
- your target is 50x50x144mm (Cu case) and your electron beam has a
kinetic energy of 2.04 GeV
- running your input file and processing it with 'usysuw' we could
reproduce the plot you're sending (using the total cumulative)
- given the dimensions of your target and the way you use USRYIELD you
observe not only the single interactions but you are also affected by
absorption (function of geometry,...), e.g., changing your input to a
shorter target results as expected in a peak at lower angles
important remark: the values from USRYILD are normalized as double
differential: dN/dE/dOmega. In order to get integrated results you still
have to multiply by the solid angle (unfortunately the statement in the
usysuw output is a bit misleading!)
another option: in case you want to score on the interaction level set
WHAT(4) and WHAT(5) in your USRYIELD card to -1. and -2. respectively ->
this means that you score neutrons as they come out from interactions
and not as they come out from the target. As mentioned before, the two
cases are only equivalent in the case of a thin target.
hope this helps, cheers
Markus
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> -----Original Message-----
> From: owner-fluka-discuss@fisica.unimi.it
> [mailto:owner-fluka-discuss@fisica.unimi.it] On Behalf Of Sunil C.
> Sent: 02 February 2007 05:47
> To: fluka-discuss@fluka.org
> Subject: Photoneutron Yiled
>
> Hi
>
> Thanks Mario for the references. The link pointing to CERN
> ref is is in French. IS there an English version?
> Regarding the isotropocity I have seen some calculation that
> predict symmetric behavior around 90 degree in the CM frame
> for any compound nucleus systems.
> Since GDR is the predominant component in the photo nuclear
> reactions even at
> 2 GeV, the photo neutrons would be from a compound nucleus
> like system. For Photons, CM and lab would not be much
> different and probably this behaviour.
>
> As for Nisy's question, The forward direction is always 10
> radiation lengths while the lateral dimensions are 5 cm
> height and 5 cm width for all target elements.Even for Cu
> these lateral dimensions would be almost 4 radiation lenghts.
> But for say W, whose radiation length is 0.35 cm (IAEA 188)
> these lateral dimensions are almost 10 radiation lengths
> which is what my forward thickness is. W shows a dip at 90
> degree instead of peak. So does U. Pb shows a mild peak at 90 degree.
> I have attached an input for the case of Cu and plots of
> angular distribution of photoneutrons in n/sr divided by the
> incident electron energy.
>
> Regards
> Sunil
>
>
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