Dear Gabriele,
I copy here a few sentences extracted from a paper on Monte Carlo that
I wrote some years ago with two other FLUKA authors:
A. Fassò, A. Ferrari, and P. R. Sala
Radiation transport calculations and simulations
Radiat. Prot. Dosimetry (2009) 137 (1-2): 118-133
Most Monte Carlo programs require a static material definition: but of
course in these conditions it is not possible to handle problems such as
burnup in nuclear reactors, where an intense neutron field modifies the
isotope composition of a material. To simulate such a situation, it must
be pointed out that the usual normalization per primary particle is not
possible: burnup is not linear with the number of primary particles,
since it depends on the source intensity. Approximations are possible by
splitting the calculation in several successive steps
[see C. Rubbia et al. (1995) Conceptual Design of a Fast Neutron Operated
High Power Energy Amplifier, CERN report CERN/AT/95-44 (EET)]
(You can get Rubbia's paper on the CERN Document Server
http://cds.cern.ch/ )
Here I would add another consideration.
While "splitting the calculation in several successive steps" is feasible
for reactor calculations, where the neutron flux, and therefore the new
composition of the material, can be considered more or less uniform over
large regions, things are more complicated in an accelerator target, where
isotope production is not uniform. In that case even the target region must be
splitted into smaller ones. Maybe one can think about a future when isotope
production could be calculated in voxels?
Alberto Fassò
On Wed, 3 Sep 2014, Firpo Gabriele wrote:
> Dear Chris,
> Thank, yoou 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 ?d are decay constants , ?(E,t) is the magnitude of the particle flux of energy E and ?ij 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 ?ij 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
> Prima di stampare questa comunicazione consideratene, per favore, l'impatto ambientale
> Please consider the environment before printing this email.
>
> ________________________________
>
> Il presente messaggio ed ogni suo allegato sono da intendersi inviati esclusivamente agli effettivi destinatari e potrebbero essere soggetti a restrizioni legali. Se avete ricevuto questo messaggio per errore Vi invitiamo a darne immediata notifica al destinatario e cancellarlo dal Vostro sistema. Qualsiasi altro uso di questo messaggio da parte Vostra è strettamente proibito. Grazie per la Vostra collaborazione.
>
> This e-mail, and any file attached to it, is meant for only the intended recipient of the transmission and may be a communication privileged by law. If you have received it in error, please notify the sender immediately and delete the original from your system. Any other use of this e-mail by you is prohibited. Thank you in advance for your cooperation.
>
>
>
> P
> Prima di stampare questa comunicazione consideratene, per favore, l'impatto ambientale
> Please consider the environment before printing this email.
>
> ________________________________
>
> Il presente messaggio ed ogni suo allegato sono da intendersi inviati esclusivamente agli effettivi destinatari e potrebbero essere soggetti a restrizioni legali. Se avete ricevuto questo messaggio per errore Vi invitiamo a darne immediata notifica al destinatario e cancellarlo dal Vostro sistema. Qualsiasi altro uso di questo messaggio da parte Vostra è strettamente proibito. Grazie per la Vostra collaborazione.
>
> This e-mail, and any file attached to it, is meant for only the intended recipient of the transmission and may be a communication privileged by law. If you have received it in error, please notify the sender immediately and delete the original from your system. Any other use of this e-mail by you is prohibited. Thank you in advance for your cooperation.
>
>
>
> P
> Prima di stampare questa comunicazione consideratene, per favore, l'impatto ambientale
> Please consider the environment before printing this email.
>
> ________________________________
>
> Il presente messaggio ed ogni suo allegato sono da intendersi inviati esclusivamente agli effettivi destinatari e potrebbero essere soggetti a restrizioni legali. Se avete ricevuto questo messaggio per errore Vi invitiamo a darne immediata notifica al destinatario e cancellarlo dal Vostro sistema. Qualsiasi altro uso di questo messaggio da parte Vostra è strettamente proibito. Grazie per la Vostra collaborazione.
>
> This e-mail, and any file attached to it, is meant for only the intended recipient of the transmission and may be a communication privileged by law. If you have received it in error, please notify the sender immediately and delete the original from your system. Any other use of this e-mail by you is prohibited. Thank you in advance for your cooperation.
>
>
>
> P
> Prima di stampare questa comunicazione consideratene, per favore, l'impatto ambientale
> Please consider the environment before printing this email.
>
> ________________________________
>
> Il presente messaggio ed ogni suo allegato sono da intendersi inviati esclusivamente agli effettivi destinatari e potrebbero essere soggetti a restrizioni legali. Se avete ricevuto questo messaggio per errore Vi invitiamo a darne immediata notifica al destinatario e cancellarlo dal Vostro sistema. Qualsiasi altro uso di questo messaggio da parte Vostra è strettamente proibito. Grazie per la Vostra collaborazione.
>
> This e-mail, and any file attached to it, is meant for only the intended recipient of the transmission and may be a communication privileged by law. If you have received it in error, please notify the sender immediately and delete the original from your system. Any other use of this e-mail by you is prohibited. Thank you in advance for your cooperation.
>
>
>
> P
> Prima di stampare questa comunicazione consideratene, per favore, l'impatto ambientale
> Please consider the environment before printing this email.
>
> ________________________________
>
> Il presente messaggio ed ogni suo allegato sono da intendersi inviati esclusivamente agli effettivi destinatari e potrebbero essere soggetti a restrizioni legali. Se avete ricevuto questo messaggio per errore Vi invitiamo a darne immediata notifica al destinatario e cancellarlo dal Vostro sistema. Qualsiasi altro uso di questo messaggio da parte Vostra è strettamente proibito. Grazie per la Vostra collaborazione.
>
> This e-mail, and any file attached to it, is meant for only the intended recipient of the transmission and may be a communication privileged by law. If you have received it in error, please notify the sender immediately and delete the original from your system. Any other use of this e-mail by you is prohibited. Thank you in advance for your cooperation.
>
--
Alberto Fasso`
SLAC-RP, MS 48, 2575 Sand Hill Road, Menlo Park CA 94025
Phone: (1 650) 926 4762 Fax: (1 650) 926 3569
fasso_at_slac.stanford.edu
Received on Thu Sep 04 2014 - 12:03:59 CEST
