Re: [fluka-discuss]: neutrons, reaction rates

From: Angel <a.demerdzhiev_at_phys.uni-sofia.bg>
Date: Tue, 6 Nov 2018 17:05:11 +0200

Dear Andrea,

thank you for the support I really appreciate it!

I did not define decay times or use the DCYSCORE card because I needed
results presented in nuclei/primary (source neutron) rather then Bq. Do I
understand correctly what I get? In the current case I suppose that I
score the number of residual nuclei of a given isotope per source neutron
in the whole volume of the detector. If I need to score
nuclei/primary/cm^3 then I should divide by the volume of the detector by
typing the correct volume in cm in the RESNUCLE card.

I modified the geometry (please find .inp attached) by placing the
activation foils on every 5 cm and changed the shape of one of th Nb
detector from box to cylinder (it is how it is supposed to be initially),
and this changed the situation. This resulted that the decline of 92mNb
nuclei per/ source neutron is faster and the difference between mine
results and the ones I am comparing with is now about 2.5-4 times. Could
such behavior be expected?

Kind regards,
Angel

> Hi Angel,
>    in your case a normalization volume WHAT(6)=1 in the RESNUCLEI
> card will not be necessary: it just just a number by which the final
> score is divided.
>
> Regarding the irradiation profile, if I understand correctly your
> problem, I see that you have not defined ant DCYTIMES card nor a
> DCYSCORE card: in this case, as stated in the manual under DCYSCORE,
> no particles originated from radioactive decay can be scored and
> any detector will only score the prompt particles. This might be
> the source of the behaviour you observe. I think thst you need
> to define DCYTIMES (a 0 value means EOB) and DCYSCORES associated
> to your RESNUCLEI cards (details in the manual).
>
> In addition, I suggest you to enable full ion transport with:
>
> IONTRANS -2
>
> to have a more accurate energy deposit by fission fragments and
> fragments from Fermi break-up.
>
> The isomers patch is not active when simulating analog decays.
>
> I send you a second revised input, where I score, for example,
> residual nuclei after 1h from EOB and I see 92mNb. I save the
> output in a separate file (UNIT=24). Please, give it a try...
>
> Hope this helps,
> Andrea
>
> Il 31/10/2018 10:46, Angel ha scritto:
>> Dear Andrea,
>>
>> thank you so much for the help and the advice! The results I'm comparing
>> with are presented as [x10^-24/nuclide/source neutron] (I suppose the
>> 10^-24 stands for barn). Thus I thought there is no need to normalize
>> it.
>> Anyway normalizing it made the results to differ even with additional
>> one
>> order of magnitude.
>>
>> I also tried to change the irradiation profile but it doesn't seem to
>> have
>> any effect - I get the same numbers. Is this expected for this model?
>> Maybe I should try to change the beam profile?
>>
>> What should be scored in the Nb detector/foil is the isomer 92mNb. So I
>> also tried switching on the patching for isomers but it is probably
>> activated by default thus that didn't have effect.
>>
>> To have proper results for 198Au I need much better statistics. Thus my
>> idea was to deal first with the 92mNb before running the model with more
>> primaries.
>>
>> Best regards,
>> Angel
>>
>>> Dear Angel,
>>>    you are missing the correct volumes in the RESNUCLEI cards (that
>>> in your case are 0.1 for NbDet and 0.00025 for AuDet regions). This
>> volume is used to normalized the results and is needed if you want to
>> compare with experimental results. If you add the correct values, you
>> should get more reasonable results.
>>> Other minor things I noticed in your input:
>>> - when defining a material, if you need the natural isotopic
>>>   composition, use WHAT(6)=0 and do not specify WHAT(2)
>>>   (see also the manual);
>>> - you can skip Z definition in a MATERIAL for a COMPOUND:
>>>   it is ignored.
>>> I attach a revised copy of the input file.
>>> Hope this helps,
>>> Andrea
>>> Il 30/10/2018 13:21, Angel Demerdzhiev ha scritto:
>>>> Dear FLUKA experts and users,
>>>> I am a beginner trying to calculate the reaction rates at different
>>>> depths
>>>> in a concrete block in Nb and Au activation foil for a 14.1 MeV
>>>> neutron
>> source.
>>>> For a reason not known to me I get results which differ in two orders
>> of
>>>> magnitude of what is expected. Can you take a squiz at my .inp file
>>>> and
>> tell me if I am doing anything wrong.
>>>> Kind regards,
>>>> Angel
>>> --
>>> ========================================================================
>> 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
>>> ========================================================================
>>
>>
>>
>
> --
> ========================================================================
> 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
> ========================================================================
>
>


-- 




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Received on Tue Nov 06 2018 - 17:40:48 CET

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