From: Stefan Roesler (Stefan.Roesler@cern.ch)
Date: Tue May 15 2007 - 17:59:24 CEST
Dear Vincent,
In addition to what Sebastien wrote (i.e., there is no model for nuclear
interactions below 100MeV/nucleon in the distributed version) you are
using
PHYSICS 1.0 0.001 IONSPLIT
which splits the deutron into its nucleons before being transported. This
way you always get at minimum one neutron, which is unphysical in this
case.
Greetings
Stefan
-----Original Message-----
From: owner-fluka-discuss@mi.infn.it on behalf of Sebastien WURTH
Sent: Tue 5/15/2007 5:28 PM
To: Feracci Vincent
Cc: fluka-discuss@fluka.org
Subject: Re: Problem with deuton converter
Hello Vincent,
Your beam energy is too low to get interactions through DPMJET (it is
transparent here). I did a SPIRAL2 simulation with FLUKA, and although
it wasn't the purpose of my study, I scored neutron fluence in the
converter (a cylinder of 7.7 cm radius and 1 cm thick) : 2.17e+14
n/cm²/s (with usrtrack then) and coming out from converter (usrbdx over
4 pi) : 1.17e+14 n/cm²/s. My beam was not cylindrical but rectangular
3cm*3cm, 40 MeV, 5 mA (ie 3.125e+16 d/s).
I found that is was not so far of the given values for 2.83 and 4 cm
beam diameters respectively 1.1e+14 and 7e+13 n/cm²/s.
I read that the neutron yield should be ~2.5% per deuteron over 4pi.
Regards.
Sébastien.
Feracci Vincent a écrit :
> Hello Fluka users,
> I am simulating the bombardment of a cylindric graphite converter (8
> cm diameter, 1 cm thick) by a 40 MeV deuton beam (gaussian spatial
> repartition) in order to produce neutrons. However in my simulation I
> measure a convertion factor which is close to 1 ( 1 deuton creates 1.1
> neutron) while it should be, according to other simulations and
> experiments about 0.01. In order to take into account deuton
> interaction, I used the following parameters:
> DEFAULTS
> PRECISIO
> EVENTYPE 2.0
> DPMJET (i have linked the DPMJET library)
> PHYSICS 1.0
> COALESCE
> PHYSICS 3.0
> EVAPORAT
> PHYSICS 1.0 0.001
> IONSPLIT
>
> LOW-NEUT 72.0 22.0 0.0196 1.0
> I used Usrtrack and Usrbdx to measure fluence inside the converter and
> at given angles of the incident deuton beam. I run my calculations on
> FLAIR V0.4 and simulated with 20.000.000 primaries separated in 50 runs.
> I am unsure of the physics models I have used but I can't manage to
> understand what is wrong with my simulation. I have attached my input
> file to this mail. Is it a problem of energy threshold for the deutons
> who by consequence all split to give neutrons?
> Thanks in advance,
>
> Vincent Feracci
> Intern at the GANIL on SPIRAL2 project
> feracci@ganil.fr
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