Re: [fluka-discuss]: Problem using USRBDX between VACUUM and other materials

From: Stefan Roesler <sroesler_at_mail.cern.ch>
Date: Fri, 9 May 2014 19:33:52 +0200

Hi Angelo

Your current scoring of BEAMPART goes up to the beam energy of 16.5MeV.
Defining a momentum spread will of course give you energies outside of the
scoring interval. Even removing the momentum spread may cause rounding
issues during scoring... If you increase the upper energy bin limit in
USRBDX to include all beam particle energies you will get the expected
fluence.

cheers
stefan




On Thu, 8 May 2014, Angelo Infantino wrote:

>
> Dear FLUKA experts,
>
> I encountered a problem using a USRBDX card between a region made of VACUUM and a
> region made of another material.
>
> In order to submit to you my problem, I have created a simple geometry that reproduces
> the problem that I have encountered in a more complex one.
>
> In this case, a proton beam hits a series of cylinders made of HAVAR, Helium and
> Copper. The cylinders are surrounded by a VACUUM region. The beam has a Gaussian
> profile in x and y and a Gaussian dp (FWHM are indicated in the .inp file attached).
>
> The setup is made in order to have a current equal to 1 primary particles crossing each
> surface per each primary, and to measure it, I set 3 USRBDX cards.
>
> The results of the USRBDX cards (total response) are:
>
>
> VACCUM->HAVAR: 0.5008144 +/- 3.7946492E-02 %
>
> HAVAR->HELIUM: 0.9997264 +/- 9.6343772E-04 %
>
> HELIUM->COPPER: 0.9997200 +/- 9.3791331E-04 %
>
>
> It is not clear why the intensity particles crossing the vacuum - Havar interface is
> one half of the expected value, noting that in the following layers I obtain the
> correct score.
>
>
> I performed 2 other tests: In the first case, I used AIR with a very low pressure
> (10^-10 bar) instead VACUUM and I obtained:
>
>
> VACCUM->HAVAR: 0.9997360 +/- 5.1841751E-04 %
>
> HAVAR->HELIUM: 0.9994880 +/- 6.2811439E-04 %
>
> HELIUM->COPPER: 0.9994496 +/- 7.2228437E-04 %
>
>
> Going in deep, I used VACUUM and removed the dp in the BEAM card. In this last case the
> results obtained are:
>
>
> VACCUM->HAVAR: 1.000000 +/- 0.000000 % (all the particles cross the surface as
> aspected)
>
> HAVAR->HELIUM: 0.9997344 +/- 4.5384694E-04 %
>
> HELIUM->COPPER: 0.9997216 +/- 4.0026353E-04 %
>
>
> From these data, seems that the problem appears using the combination of dp in the BEAM
> card and VACUUM as material.
>
> Can someone explain this strange behavior?
>
> Attached there is my .inp file.
>
> Best regards
>
>
> Angelo Infantino
>
>
>
Received on Fri May 09 2014 - 20:42:09 CEST