Dear Evgeny,
I am checking your input file and, at a first sight, I would
recommend you to repeat the calculation by using the PRECISION defaults,
instead of the NEUTRONS defaults, as you did.
If you look in the Fluka manual, with PRECISION Fluka will perform
a more detailed simulation, in particular with a "fully analogue
absorption for low-energy neutrons", lower thresholds for several
reactions and several other more precise default options. With
NEUTRONS you have instead "Non analogue absorption for low-energy
neutrons with probability 0.95 for the last (thermal) groups".
Moreover, I am not sure about the Geant4 and MCNP settings, but
these kind of comparisons are always "tricky" and require some
experience in the tuning of the different codes...
Hope this helps.
Andrea
On 18/04/2019 14:18, kem002_at_campus.mephi.ru wrote:
> Dear FLUKA users,
>
> I am a beginner, so I'm sorry for the potential silly question.
>
> The problem is shown in the following situation:
> 1. I use low energy pencil neutron beam (2 MeV)
> 2. In distance of 20 cm, I dispose of a sphere with a radius of 4.55
> cm filled by Pu239 material with a density of 15.7 g/cm3.
> 3. Behind the plutonium, I also set the detector in a distance of 40
> cm. It represents water sphere with a radius of 20 cm.
> The geometry has axial symmetry. (Fig. 1)
>
> I calculated the energy spectrum in the detector with USRTRACK card. I
> also calculate this problem with Geant4 toolkit and asked my colleague
> to calculate this on MCNP.
>
> I obtained different spectra between Fluka and MCNP/Geant4. The
> difference appears in neutron amount, the Fluka has lower than
> MCNP/Geant4, but spectrum form is the same. (Fig. 2)
>
> I suppose it is a result of lower secondary neutron production in
> Fluka for comparison with MCNP (3.42 vs 6.45 [fission neutrons /
> primary particle]). After normalizing spectrums on these coefficients,
> they convergent quite well. (Fig. 3)
>
> I can't understand where is the problem. I suppose I could miss some
> cards in Fluka, that 'turn on' some physic processes or something like
> this.
>
> I also concerned about the percentage of secondaries in Fluka output.
> It shows 100% as the number of all secondaries but in the listing
> below it hardly half of this amount. (Fig. 4)
>
> I attach my input file and images to this message.
>
> Sincerely,
> Evgeny Kolodin
> postgraduate student, MEPhI
--
========================================================================
Dr. Andrea Fontana tel: +39 0382 987991
Istituto Nazionale fax: +39 0382 423241
di Fisica Nucleare
Sezione di Pavia e-mail: andrea.fontana_at_pv.infn.it
Via Bassi 6 web : www.pv.infn.it/~fontana
27100 PAVIA, Italy
========================================================================
__________________________________________________________________________
You can manage unsubscription from this mailing list at https://www.fluka.org/fluka.php?id=acc_info
Received on Thu Apr 18 2019 - 18:34:21 CEST