Re: O-16(gamma, alpha)C-12 and N-14(gamma,p)C-13 cross sections below 9MeV

From: Mina Nozar <nozarm_at_triumf.ca>
Date: Mon, 29 Jul 2013 18:35:55 -0700

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Dear Alberto,

Thank you for the information. I must admit, I have not been reading
the RELEASE notes in the past few installation.

- Is there a way to estimate how much an underestimation we are talking
about?
- Is it possible to estimate when present fission models will be
integrated into FLUKA?

Thank you and best wishes,
Mina


On 13-07-25 02:23 AM, Fasso, Alberto wrote:
> Dear Mina,
>
> I hate to say it, but at this moment photofission is not handled very well in FLUKA.
> In the Release Notes which are distributed with the code, there is the following
> statement:
>
> - There is a known issue with photofission: the photonuclear interaction
> model is not up-to-date with respect to the present fission model.
> As a result, photofission can be heavily underestimated at low photon
> energies for fissile materials. A fix is in progress and it will be
> included in a future patch release.
>
> I hope that this problem will be solved soon.
>
> The models used in the code to calculate total photo-nuclear reactions are
> shortly described in the attached paper, which was presented at the 8th Int. Conf. on
> Radiation Shielding, Arlington (Texas) Apr. 24-28 (1994). What is described in the paper,
> is the initial excitation of the nucleus by the photon. The de-excitation which follows
> is handled by the usual FLUKA hadronic models, that you find described in some
> papers listed on the FLUKA website:
> http://www.fluka.org/fluka.php?id=publications&mm2=3
> Nuclear models in FLUKA: present capabilities, open problems and future improvements
> F. Ballarini et al.
> The physics models of FLUKA: status and recent developments
> A. FassÚ et al.
> Unfortunately the publication database has not been updated since 2004: perhaps some
> of my colleagues will be able to point you to some more recent articles.
>
> About your last question: "What do the "All, Spalltion, and Low Energy" settings mean in the
> context of photo-induced reactions with the RESNUCLE card?", the answer is that the
> meaning of "Low Energy" concerns only neutrons, which, as you know, in FLUKA are
> transported in a special way. So, "All" and "Spallation" are equivalent for photon-produced
> nuclei (in the same way as for all other particles except low-energy neutrons).
>
> Kind regards,
>
> Alberto
>
> ________________________________________
> From: Mina Nozar [nozarm_at_triumf.ca]
> Sent: Wednesday, July 24, 2013 12:58 PM
> To: Fasso, Alberto
> Cc: fluka-discuss_at_fluka.org; George Kharashvili
> Subject: Re: O-16(gamma, alpha)C-12 and N-14(gamma,p)C-13 cross sections below 9MeV
>
> Dear Alberto,
>
> On a related topic, we are also interested in how photonuclear reactions
> are handled in FLUKA, in particular, photo-induced fissions. We are
> trying to compare production rates for certain radio-isotopes produced
> in photo-fission off of a depleted Uranium target with neutron-induced
> rates.
>
> How is photo-fission handled in FLUKA?
>
> Is there a paper/reference that describes all the models used in the
> code to calculate total photo-nuclear reactions, and all the reactions
> considered?
>
> Also, What do the "All, Spalltion, and Low Energy" settings mean in the
> context of photo-induced reactions with the RESNUCLE card?
>
> Many thanks,
> Mina
>
> On 13-07-17 02:40 AM, Alberto Fasso' wrote:
>> Hi George,
>>
>> for photonuclear reactions, FLUKA uses only TOTAL cross sections: it
>> uses them
>> to determine the point of interaction. The interaction is simulated by
>> one or
>> more models ("event generators"): evaporation, pre-equilibrium, Fermi
>> breakup,
>> etc.) The particular partial reaction, in your case (gamma,p) or
>> (gamma, alpha), is the result of the event generator, not the input to
>> it.
>> So, to answer your first question: what you find with your
>> "experiment" are not
>> the cross-sections "used" by FLUKA, but the cross sections
>> "calculated" by
>> FLUKA. The only cross sections used are the total ones (gamma,n +
>> gamma,p +
>> gamma,alpha, + gamma,2n + gamma,pn,....)
>>
>> In answer to your second question, if those cross sections
>> significantly differ
>> from the experimental data (I hope not!) the only way to change your
>> results
>> would be to change the models, which is obviously impossible. There
>> are no
>> partial cross sections available in the code, so none that can be
>> changed.
>>
>> You can still calculate photon energy spectra, and fold them with the
>> cross sections you prefer, but I don't think that this is what you are
>> looking for.
>>
>> Alberto
>>
>> On Tue, 16 Jul 2013, George Kharashvili wrote:
>>
>>> Dear FLUKA experts,
>>>
>>> We are interested in O-16(gamma, alpha)C-12 and N-14(gamma,p)C-13
>>> reactions
>>> below 9MeV. We set up FLUKA models with thin targets and
>>> "experimentally"
>>> determined the cross-sections. Sample input file and derived
>>> cross-sections
>>> are attached.
>>>
>>> The model is simple: photon beam is incident on 1% radiation length
>>> target.
>>> Photon and e-/e+ production and transport thresholds are set to 20
>>> keV below
>>> the beam energy. Number of alphas is scored in the target region.
>>> This is
>>> repeated for beam energies between 7.2 and 9.2 MeV in 20 keV steps.
>>>
>>> We would like to know:
>>> 1. If this is the best way to find out the cross-sections used by FLUKA;
>>> 2. If we determine that the cross-sections in FLUKA significantly differ
>>> from the experimental data, is there a way to run FLUKA using our custom
>>> tabulated cross-sections.
>>>
>>> Thank you in advance for your time.
>>>
>>> -George Kharashvili
> >
Received on Tue Jul 30 2013 - 11:55:42 CEST

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