Dear Mr Fontana,
Thanks for your response. I also calculated that problem with PRECISION
defaults, but the results are the same.
I agree with you that comparison with some other codes may be wrong
because I could make mistakes in them also.
To abstract from other codes and the possibility of mistakes, I suppose
to conduct simulations with critical Pu assembly. For Pu239 critical
mass is close to 11 kg. For 15.7 g/cm3 density, it gives us a critical
radius of Pu sphere of 5.51 cm.
Next, I increase the radius of Pu sphere in my problem to 7.0 cm. For
now, I expect the program termination in reason of particles stack
overflow. But calculations are going on. I can't understand why.
Sincerely,
Evgeny Kolodin
postgraduate student, MEPhI
Andrea Fontana wrote 2019-04-18 18:13:
> 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
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Received on Fri Apr 19 2019 - 16:44:57 CEST