Re: [fluka-discuss]: I: momentum spread with source routine

From: Giuseppe Battistoni <giuseppe.battistoni_at_mi.infn.it>
Date: Wed, 12 Jan 2022 18:06:16 +0100

Hi Daria

I see that in the source routine you write:


*  |  Kinetic energy of the particle (GeV)
          TKEFLK (NPFLKA) = SQRT ( PMOFLK (NPFLKA)**2 + AM (IONID)**2 )
      &                   - AM (IONID)
*  |  Particle momentum
          CALL FLNRRN(RGAUS_MO)
          PMOSPR=WHASOU(5)/2.355
          PMOFLK (NPFLKA) = PBEAM*(ONEONE+PMOSPR*RGAUS_MO)
*

So you first calculate the kinetic energy and after that you fluctuate
the momentum. This could be inconsistent.

Try instead to write:

*  |  Particle momentum
          CALL FLNRRN(RGAUS_MO)
          PMOSPR=WHASOU(5)/2.355
          PMOFLK (NPFLKA) = PBEAM*(ONEONE+PMOSPR*RGAUS_MO)
*  |  Kinetic energy of the particle (GeV)
          TKEFLK (NPFLKA) = SQRT ( PMOFLK (NPFLKA)**2 + AM (IONID)**2 )
      &                   - AM (IONID)

So you calculate a kinetic energy consistent with the fluctuated momentum.

I do not know if this is the solution, but I invite you to test it.

Ciao
         Giuseppe

On 12/01/2022 11:31, Boscolo, Daria Dr. wrote:
> Dear FLUKA experts,
>
> I am trying to implement a gaussian momentum spread with the source routine as it is in the beam card.
> To do that I followed the indication given in a previous discussion in this forum:
> http://www.fluka.org/web_archive/earchive/new-fluka-discuss/18392.html
>
> However, the distribution I obtain does not match with the one I see when using the beam card: the two results differ of about a 30% on the momentum spread sigma.
>
> I attach here a plot of the two energy spectra together with the two input files and the source routine I am using.
>
> Many thanks for the help,
> Best regards,
> Daria
>
> --
> Dr. Daria Boscolo
> Biophysics / Biophysik
>
> Phone / Telefon: +49 6159 71 1650
> Fax: +49 6159 71 2106
> Mail: d.boscolo_at_gsi.de
> Location: SB2.3.188
>
> GSI Helmholtzzentrum für Schwerionenforschung GmbH
> Planckstraße 1, 64291 Darmstadt, Germany, www.gsi.de

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Received on Wed Jan 12 2022 - 19:50:01 CET

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