Isotopic composition of the fluka material

Dear FLUKA experts,

I am now doing some calculations to estimate the residual activities induced by high-energy electrons.
The preliminary result predicted by FLUKA seem reasonable for my very simple case.
As you know, what radionuclides could be produced definitely depends on the actual isotopic composition of target.
Therfore I wonder what exactly the isotopic composition of my target is?
I defined my Iron target using the following command:
MATERIAL 26. 55.847 7.87 11. IRON
The WHAT(6) for the mass number is omitted.
According to the manual, the natural isotopic composition is used.
I know I can define my own isotopic compoistion of iron using the MATERIAL&COMPUND cards.
But I still want to know:
What natural isotopic compoistions are implemented in fluka code and where can I get access to the information?
Because minor difference may exist between different sources in the so-called natural abundnace of nuclides.
And is there any significant effect for the atomic weight that given by user through WHAT(2)?
For example, if I give the atomic weight of iron,say 55.8, is it OK?
Thanks in advance

Rong-Jiun Sheu
NSRRC, Taiwan
Received on Thu Jun 26 16:38:48 2008