Re: FLUKA: photonuclear cross section data base
Dear Alberto,
thank you very much for this detailed first answer. Excuse me please
for further questions.
Alberto Fasso' wrote:
>
> Dear Baerbel,
>
> I will try to answer your questions.
>
> > 1) Pb :
> > Comparing with experimental data from the EXFOR data base (NEA)
> > for 208-Pb and 206-Pb I found a good agreement with the FLUKA
> > parameterization and I assumed, that the shape of the cross
> > section curves describes the total photonuclear cross section.
> > >>> Is this right, or not ??
>
> Yes and no. In principle FLUKA uses total photonuclear cross
> sections, but experimental data exist only for a few light nuclides.
> For heavy nuclei, the total cross section is practically identical
> to the (gamma,Sn) cross section, i.e.:
> (gamma,n)+(gamma,np)+(gamma,2n)+(gamma,3n)+ ...+(gamma,fission)
> [note that this is different from the (gamma,Tn) cross section
> (neutron yield cross section), which is:
> gamma,n)+(gamma,np)+2(gamma,2n)+3(gamma,3n)+ ...+nu(gamma,fission)]
> The reason that sigma(gamma,Sn)=sigma{gamma,total) is that for large Z the
> Coulomb barrier is too high to allow emission of charged particles.
>
> So, in FLUKA we use at the moment:
> a) Experimental total cross section data if they exist:
> 3He, 7Li, 9Be, 12C, 13C, 14N, 15N, 16O, 17O, 18O, 19F, 23Na,
> 24Mg, 25Mg, 26Mg, 27Al, 29Si, 30Si, natSi, 32S, 34S, natCa
> - Otherwise:
> For Z > 29:
> b) a Lorentz parametrization with published Lorentz parameters
> (peak energy, peak height, width), if they exist. They are
> all those reported in the Atlas of Dietrich and Berman
> Atomic Data and Nuclear Data Tables 38, 199 (1988), except
> Pr, Au and Pb, for which we have used the parameters
> published in Berman et al., Phys. Rev. C36, 1286 (1987).
> - Otherwise:
> c) a Lorentz parametrization with parametrized Lorentz parameters
> (it sounds funny, but Berman and Fultz (Rev. Mod. Phys. 47,
> 713 (1975) have published some general formulas giving the 3
> Lorentz parameters as a function of A and Z.)
I found this reference and I have to study it in the next days. That's
anyone's guess, that in the case of 204-Pb is an bug in the
paramerization
extracted with the function XTGNUC as seen in the figure wq_anfrage.ps.
If it is possible could you have, please, a look at the corresponding
program
part of FLUKA ?
If the parameters for the 204-Pb photonuclear cross section were defined
by
formulas as a function of A and Z only (and not additionally the
percentage of
the abundance of the nuclide in natural composition), than :
>>> Why the cross section is so small in the FLUKA paramerization as seen
in the figure wq_anfrage.ps ? <<<
Can anybody try to use this formula to a known nucide like in a) (see
above) to
test the consistence ? Or, is there a possibility for FLUKA users to
change the
Lorentz parameters "by hand" ? Can I do some checks myself ?
> For Z <= 29, total cross section obtained as:
> d) sum of partial cross sections: 4He
> e) difference sigma(nat. composition) minus sigma(available isotopes):
> 28Si
> f) sigma(gamma,Sn) or sigma(gamma,Tn) corrected by PEANUT:
> 6Li, 10B, 11B, 31P, 35Cl, 37Cl, 40Ar, natK, 42Ca, 45Sc, 48Ti, 50Ti,
> 51V, natCr, 55Mn, natFe, 59Co, 60Ni, 63Cu, natCu
> g) the parametrized formula of Berman and Fultz for all nuclides not
> listed above, with an empirical correction for low-Z. This can be
> very bad in some cases (e.g. 58Ni), and we will try to improve it.
>
> Please note that the quality of these data can be:
> good: cases a), b), d)
> fair: c), e), f)
> poor: g)
>
> > Unfortunately I could not found any evaluated or experimental
> > photoneutron cross section data for the isotope 204-Pb (with an
> > abundance of 1.4 %) to compare these data with the FLUKA
> > paramerization. This cross section seems to be too small.
> > This Pb-isotope is responsible for the major contribution of
> > activity of the lead radiator and it is very important to use the
> > correct cross section values. There, I want to ask the authors,
> > how the photonuclear (photoneutron) cross section parameterization
> > was obtained for 204-Pb ?
> > Could you, please, comment this question ?
>
> The answer for 204Pb is case c) above.
>
> > 2)Hg :
> > We compared the results of the neutron emission for the lead
> > radiator with results for a mercury radiator. The neutron flux
> > for Hg is approximately four times smaller as for Pb. Looking at
> > the photonuclear (photoneutron) cross sections it seems, that in
> > the case of Hg nuclides the cross sections are normalized
> > proportional to the percentage of the natural abundance of the
> > Hg-isotopes ? In the Berman Compilation I found, that the maximum
> > cross section of nat. Hg amounts to 600 mb. I could not found any
> > other cross section data for Hg, e.g. in the NEA data bank.
> > How good are the cross section parameterizations for the
> > Hg-isotopes used in the program FLUKA ?
>
> In this moment I don't have the Dietrich-Berman Atlas at hand: if Hg is
> not in that list, then also for it we use the "parametrized Lorentz
> parameters" of case c).
Here are the values from the Berman Atlas for natural Hg :
Egamma max = 21.1 MeV
sigma int (gamma,Sn) = 3678 MeV mb
sigma int (gamma,tot) = 3133 MeV mb
sigma int (gamma,1n) = 2588 MeV mb
sigma int (gamma,2n) = 545 MeV mb
Fitting interval : 11 - 17 MeV
Lorentz Parameters :
Em = 13.72 MeV
sigma m1 = 582 mb
GAMMA 1 = 4.39 MeV.
Thanks for your help and best regards
Baerbel
--
Bärbel Naumann Tel. +49 351 260-3132
Technische Universität Dresden Fax. +49 351 260-3700
Institut für Kern- und Teilchenphysik B.Naumann@fz-rossendorf.de
01062 Dresden
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