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

From: Fasso, Alberto <fasso_at_slac.stanford.edu>
Date: Thu, 25 Jul 2013 02:23:12 -0700

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 Thu Jul 25 2013 - 21:48:42 CEST

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