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

From: Fasso, Alberto <>
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

- 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:
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,


From: Mina Nozar []
Sent: Wednesday, July 24, 2013 12:58 PM
To: Fasso, Alberto
Cc:; 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

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

Also, What do the "All, Spalltion, and Low Energy" settings mean in the
context of photo-induced reactions with the RESNUCLE card?

Many thanks,

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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