Date: Thu, 18 Apr 2019 15:18:54 +0300
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
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(image/png attachment: Figure_1.png)
(image/png attachment: Figure_2.png)
(image/png attachment: Figure_3.png)
(image/png attachment: Figure_4.png)
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