RE: Isotopic composition of the fluka material

Hi Rong-Jiun Sheu,

the natural composition of iron and used in FLUKA is the following:
- Fe54: 5.82
- Fe56: 91.66
- Fe57: 2.19
- Fe58: 0.33

compared e.g., to NIST:
- Fe54: 5.845
- Fe56: 91.754
- Fe57: 2.119
- Fe58: 0.282

The numbers used in FLUKA have been extracted from publications regulary updating respective 'natural' compositions. However, given the small changes (as well as natural fluctuations depending on what 'standard' is used) the last change of the fractions used in FLUKA was performed in the mid-90', whereas the atomic weight is updated on a regular basis through the different FLUKA releases. Please note that for low-E neutron cross sections (also the isotope production) for natural compositons are weighted according to the assumed fractional weight.

Concerning your question for the atomic weight, whatever you specify will certainly affect your calculations (e.g., dE/dx, as well as the total cross section). However, in your case when you're interested in isotope production from iron, I wouldn't expect any significant change when going from 55.847 to 55.8. I would think that the possible difference between the 'natural' to the 'real' one being higher.

One more comment concerning the atomic weight as specified through WHAT(2), please note that in case there is no value given, FLUKA will actually calculate the correct atomic weight corresponding to the assumed natural composition (to be also updated in the manual).

As a general comment, you might not only be interested in the actual 'natural composition' of your sample, but also in other trace elements in your iron sample. Perhaps not for iron, but for other materials these traces can be more important for isotope production than slight changes in the actual natural composition.

hope this helps, cheers

Markus

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From: owner-fluka-discuss@mi.infn.it [mailto:owner-fluka-discuss@mi.infn.it] On Behalf Of ???
Sent: Donnerstag, 26. Juni 2008 11:47
To: fluka-discuss@fluka.org
Subject: 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 Tue Jul 1 11:29:51 2008