Re: FLUKA: photonuclear cross section data base
Dear Baerbel,
perhaps you have found a problem (or even two) with the GDR cross
sections.
Using the parametrization formula "stand-alone", i.e. not running FLUKA
but in a separate test program, I get for the peak cross section of 204Pb
394.1 mb. It is still a bit too low, but much larger than what you got
using the XGTNUC routine. If I use the same formula for the other
isotopes of Pb, I get:
Pb 206: 393.8
Pb 207: 393.5
Pb 208: 393.2
They are all too low compared with the experimental values, which are of
the order of 500-600 mb, so probably we must revise our parametrization.
The formula we took from the Berman & Fultz paper I mentioned yesterday
gives only the energy of cross section maximum (and it doesn't seem too
bad). For the peak height and width, I did an empirical fit to data
which apparently should be improved.
This does not explain why you got values which are even an order of
magnitude lower. It is possible that there is a bug in the way
the formula is called: I will look into it as soon as possible.
I must say that implementing the photonuclear cross sections is a
long-lasting process: our choice was to provide "some" cross section
from the beginning for all possible isotopes, and to go on improving
with higher priority the most common ones (or the most important).
Therefore, the effort so far has been in improving the treatment of
low-Z materials, which are important for shielding (concrete) and for
dosimetry (tissue), and for which it was known that parametrizations
cannot be applied at all. The Lorentz parameters of Dietrich-Berman and
the low-Z data cover now most of the materials one can find in practical
cases. Still, we must aim at getting a reasonable accuracy even for
the more rare nuclides.
Your questions made me realize that we have now to look better at
the "catch-all" formulae we use for the materials for which no data at
all is available. Thank you for getting our attention on them
Alberto
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