Re: The error

From: Anna Ferrari <>
Date: Wed, 29 Jul 2009 11:26:19 +0200 (CEST)

 Dear Andrzej,

  I have two observations about the input files, that you have written
  to calculate differential cross sections of a 1 GeV/u carbon ion beam
  on a gold target (cau8.inp and cau6.inp).

  1) You heavily use the card LAM-BIAS, to reduce the interaction length
     for nuclear inelastic interacions of heavy ions by a factor 10^4.
     A such very large reduction factor is NOT recommended for hadrons,
     as explicitly written in the manual (ch. 7.37).
     As consequence of this, you get a too large (in principle not fatal)
     error messages from the GEOFAR routine, reporting a not correct
     normalization of the director cosines. This happens always close to
     the zero of your coordinate system (the center of your gold target).
     You get about 1 error every 10 events.... so finally you get a crash.

     I removed your bias and I could run 10^5 events without problems.
     Obviously without bias you have to run more primary events, but this is
     compensated by the fact that the cpu time per event is reduced
     by a very large factor.

   2) You use the STEPSIZE card, setting the maximum step = 1 cm and the
      minumum step = 0.01 cm. This does not make sense in my opinion,
      manly concerning the minimum step size: in your first input file
      you have a gold target 22 micron thick... I would comment this
      card, or I would set only the maximum step size.

   Finally, a comment about the second plot of the results, that you have
   sent in attachment in your first email. Did you have applied the
   correction by the amount of pions, that are already decayed at your
   boundary crossing?
   This is not a large correction (you used a detector at 30 cm from your
   target), but I would think that it has to be done... I would correct
   bin by bin, because the decay length in the lab system depends on the
   pion energy (you will get a correction of about 2% at low energies
  and of about 0.7% at 700 MeV...).

   Hope it helps,


     Anna F.

> Dear FLUKA users
> I tray to calculate the diff.cross sections in heavy ion colision C+Au.
> and have any error. I can't understand what is reason.
> In attachment are input file (cau8.inp) and cau8001.err and
> cau80001.out
> What I have done badly?
> Kind regards
> Andrzej
Received on Wed Jul 29 2009 - 12:09:20 CEST

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