Date: Wed, 3 Sep 2014 12:22:10 +0000
Dear Chris,
Thank you again for your reply.
I totally agree with you regarding your last sentence regarding the transmutation of the material during irradiation. In the past I had experience with “0-dimensional” activation and transmutation codes (like FIPACT and Anita-2000). In this case the user typically has to follow the so-called “two steps method” to perform material activation/transmutation studies: firstly, the average particle flux inside a slab of material has to be evaluated with a Monte Carlo code (i.e., via a track length estimator—“F4” tally in MCNP or “USRTRACK” estimator in FLUKA) and then, secondly, this flux has to be put as an input for the transmutation code. The problems are that neither (1) the change on the irradiating flux inside the slab (it can be approximately simulated by performing, in the first Monte Carlo step, a segmentation of the slab in the particle flux direction and by evaluating the averaged track length inside any slab segmentation) nor (2) on the material composition of the slab during irradiation are taken into account.
If I understood well what you said about how FLUKA works in the residual nuclei calculation, the problem (1) is solved because the changes on the irradiating flux are embedded in the calculation, whereas the problem (2) is not—again, I totally agree with you about the explanation of why it is so: numerical costly solution of the Bateman equations would be necessary if material transmutation during irradiation were taken into account. As far as I know, this is a well-known issue. Fortunately, in most of the radiation shielding problems the material transmutation during irradiation is negligible, so no other calculation instruments are needed. But this is not the case, for example, in fission and chain-reaction problems (for example, consider the Plutonium build up during neutron irradiation in nuclear reactors), where dedicated codes must be used.
[S_ORANGE_Logo_Ansaldo_Nucleare_2014]
Gabriele Firpo
Unità Reattori e Sicurezza – Reactor and Safety Engineer
C.so F.M. Perrone, 25
16152 Genova - Italia
Ph: +39.010.655.83.42
www.ansaldonucleare.it<http://www.ansaldonucleare.it/>
gabriele.firpo_at_ann.ansaldo.it<mailto:gabriele.firpo_at_ann.ansaldo.it>
Da: Chris Theis [mailto:Christian.Theis_at_cern.ch]
Inviato: mercoledì 3 settembre 2014 11:14
A: Firpo Gabriele; fluka-discuss_at_fluka.org
Oggetto: RE: Residual nuclei calculation: models or data libraries?
Hello Gabriele,
the change in the primary flux as well as the creation of the secondary showers are implicitly treated within FLUKA’s reaction model. This is done in a stochastic way and eventually the complete particle spectrum will contribute to the simulated production of residual nuclei. Once the nuclide production term is calculated it will be used as a starting point for solving the Bateman formalism analytically to obtain the isotope activities, including also decay chains.
However, I am not aware that FLUKA, at least not in the standard version, will treat transmutation of the material during irradiation. For each particle history the original material will be assumed, which for most accelerator applications should be sufficient. Ignoring transmutation will allow for devising a very efficient analytic solution to the Bateman equation via a Laplace transform. Taking the possibility of material transmutation during irradiation into account will result in identical eigenvalues which either require a numerical solution to the Bateman equations or a complex summation of many high-order derivatives, which can be computationally costly.
However, I’m not an expert on transmutation and maybe somebody else on the discussion list, who has knowledge in the application of FLUKA and transmutation, can comment on this aspect.
Cheers
Chris
From: Firpo Gabriele [mailto:Gabriele.Firpo_at_ann.ansaldo.it]
Sent: 03 September 2014 10:36
To: Chris Theis; fluka-discuss_at_fluka.org<mailto:fluka-discuss_at_fluka.org>
Subject: R: Residual nuclei calculation: models or data libraries?
Dear Chris,
Thank you very much for your answer.
I have another question about the residual nuclei calculation as implemented in FLUKA.
Let’s consider a very simple problem: energetic proton flux (E~GeV) impinging on an high-Z (steel, lead, …) material slab. Again, it is widely known that, as we go deeper and deeper inside slab thickness:
1. The proton flux is expected to become less intense and less energetic;
2. Secondary particles are generated inside the material (in particular, neutrons); these particle can significantly contribute (or dominate, depending by the case) to the material transmutation.
The question is: are these two items (decreasing of the “primary” particle flux and increasing of the “secondary” particle flux) embedded in the FLUKA residual nuclei calculation inside a region?
[S_ORANGE_Logo_Ansaldo_Nucleare_2014]
Gabriele Firpo
Unità Reattori e Sicurezza – Reactor and Safety Engineer
C.so F.M. Perrone, 25
16152 Genova - Italia
Ph: +39.010.655.83.42
www.ansaldonucleare.it<http://www.ansaldonucleare.it/>
gabriele.firpo_at_ann.ansaldo.it<mailto:gabriele.firpo_at_ann.ansaldo.it>
Da: Chris Theis [mailto:Christian.Theis_at_cern.ch]
Inviato: martedì 2 settembre 2014 12:48
A: Firpo Gabriele; fluka-discuss_at_fluka.org<mailto:fluka-discuss_at_fluka.org>
Oggetto: RE: Residual nuclei calculation: models or data libraries?
Dear Gabriele,
you can find an answer to your question in the discussion archive at:
http://www.fluka.org/web_archive/earchive/new-fluka-discuss/6308.html
Regarding the models, FLUKA uses its own model which is called PEANUT. You can find the respective references to the publications on the FLUKA website in the reference section.
Best regards
Chris
From: owner-fluka-discuss_at_mi.infn.it<mailto:owner-fluka-discuss_at_mi.infn.it> [mailto:owner-fluka-discuss_at_mi.infn.it] On Behalf Of Firpo Gabriele
Sent: 02 September 2014 12:07
To: fluka-discuss_at_fluka.org<mailto:fluka-discuss_at_fluka.org>
Subject: [fluka-discuss]: Residual nuclei calculation: models or data libraries?
Dear Fluka users,
I know that the capability to score the residual nuclei has been implemented into FLUKA with an analytical solution of the Bateman equations describing activity build-up and decay during irradiation and cooling down, for arbitrary irradiation conditions.
As it is well known, the Bateman equation for the concentration Ni of isotope i in a material subject to a particle flux reads as
[http://neutron.kth.se/courses/transmutation/Bateman/Eq1.gif]
where λd are decay constants , φ(E,t) is the magnitude of the particle flux of energy E and σij is the particle cross section for transmutation from isotope j to i (The sum is to be taken over all other nuclides j present in the material).
The question is: depending on particle irradiating type (neutron and proton in particular), does Fluka use data libraries and/or models to set the σij parameters on the Bateman equation? I suggest that data libraries are used for “low-energetic” neutrons (E<20 MeV) and models elsewhere. Is that true? If so, which kind of data libraries and models are used?
[S_ORANGE_Logo_Ansaldo_Nucleare_2014]
Gabriele Firpo
Unità Reattori e Sicurezza – Reactor and Safety Engineer
C.so F.M. Perrone, 25
16152 Genova - Italia
Ph: +39.010.655.83.42
www.ansaldonucleare.it<http://www.ansaldonucleare.it/>
gabriele.firpo_at_ann.ansaldo.it<mailto:gabriele.firpo_at_ann.ansaldo.it>
P
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