Re: [fluka-discuss]: Low energy neutron and secondary particles fluences

From: Luigi Salvatore Esposito <luigi.salvatore.esposito_at_cern.ch>
Date: Tue, 11 Dec 2018 17:01:34 +0000

Dear Thomas,

see my answers inline.

Hope this could help.

Cheers luigi


On 11 Dec 2018, at 11:05, Thomas Frosio <thomas.frosio_at_cern.ch<mailto:thomas.frosio_at_cern.ch>> wrote:

Dear Fluka expert,

I have four questions regarding low neutron transport in fluka.
I would like to simulate a very simple situation.
This situation is the following:
• I have a monoenergetic source of neutron in air (for example 9 MeV)
• I want to score neutron and secondary particle fluences at 1 m from the source

I know that low energy neutrons use the multigroup formalism and scattering matrix.
However, I am wondering how multigroup formalism impacts the simulated energy in fluka for the primary/secondary particles and for the fluence score.
My questions are the following:
-If my primary neutrons are simulated at 9 MeV, as the corresponding energy group is [8.82-9.05] MeV, should I consider the primary particle has an energy of 8.94 MeV (average).
The primary neutron will have an energy of 9 MeV as you can see from the output file (beam properties or energy balance table at the end of the file)

-If I want the total discretization of my fluence with the smallest energy mesh, should I describe fluka energy groups in my USRBDX score or is it treated automatically by putting 0.01 meV and 20 MeV for low neutron energy in WHAT4 and WHAT5 ?
no, you can’t. See note 7 of the USRBDX section in the manual.

-If I want fluences from secondary particles (gamma, neutron and charged particles), are they simulated like for gamma or electron transport or is it treated differently (with group or average factors for example).
Once generated, secondary particles are transported in the usual way.
More details in the section 10.3 of the manual. Charged particles are generated only for few reactions (10.3.3 of the manual)

-In my situation, (air + monoenergetic low neutron), is it possible to request pointwise sections for the transport? If yes, how can I do?
Pointwise transport is available only for few isotopes. It can be activated by LOW-NEUT or by some DEFAULTS (for example PRECISIOn) as explained in the manual.
For the air, you will get the contribution from 14N(n,p)14C reaction.


Thank you very much for your answer,
Salutations respectueuses,
Thomas Frosio


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Received on Tue Dec 11 2018 - 19:26:58 CET

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