Dear Evgeny,
the conditions foir particle stack overflow were discussed in the
forum a while ago. This thread might be useful:
http://www.fluka.org/web_archive/earchive/new-fluka-discuss/2399.html
Kind regards,
Andrea
On 19/04/2019 14:26, kem002_at_campus.mephi.ru wrote:
> 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
>
--
========================================================================
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 Fri Apr 19 2019 - 15:56:41 CEST