FLUKA: photonuclear cross section data base


To fluka-discuss@listbox.cern.ch
From Baerbel Naumann <B.Naumann@fz-rossendorf.de>
Date Tue, 11 Dec 2001 18:07:55 +0100
Organization Forschungszentrum Rossendorf e.V.
Reply-To Baerbel Naumann <B.Naumann@fz-rossendorf.de>
Sender owner-fluka-discuss@listbox.cern.ch

Dear FLUKA authors and FLUKA users,
I use the code FLUKA to estimate the neutron flux produced
in a thin radiator (6 mm thick) of lead (or mercury) bombarded by 
electrons with energies from 20 MeV up to 40 MeV. In this energy 
range the photonuclear interaction (photoneutron reaction) is
expected to proceed mainly via the Giant Dipole Resonance.
This kind of interaction is implemented in FLUKA by
paramerized  energy dependent cross sections for certain
nuclei.
In my calculations the used cross sections of photonuclear 
(photoneutron) reaction play a decisive role for the determination
of the neutron flux as well as for the activation of the radiator 
material.
In former times I learned from Stefan Roesler one way to 
extract the photonuclear cross sections (XSGAM) used by FLUKA : 
To get the paramerized cross section for the target nucleus of 
interest one has to call the subroutine XTGNUC(Energy,A,Z) inside
the userroutine source.f like

*Pb          XSGAM = XTGNUC(EK,204,82)
*Hg          XSGAM = XTGNUC(EK,196,80).


At present time, we investigate the two radiator materials lead and 
mercury. I extracted the photonuclear cross sections  using the 
previously described method. The found cross sections are shown
in the figure wq_anfrage.ps, I attach to this email.

Now, I have some questions concerning these data base 

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 ?? 
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 ? 

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 ?

Please, help us to understand our results. Thank you in advance 
for any help,

best regards, Baerbel Naumann

-- 
 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

wq_anfrage.ps


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