RE: xsec not found

From: Markus Brugger (
Date: Thu Dec 06 2007 - 18:36:58 CET

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    Hi Olaf,

    when using low-energy neutron transport you've to be careful how to
    specify the material (name) and in what way it relates to the respective
    low-energy neutron cross-sections available in FLUKA. In order to find
    out what material corresponds to what 'name' or parameters, please check
    the manual, e.g., directly at:

    In general the following rules apply:

    - In most cases, option LOW-MAT is not needed (however not in your
    - If a material name different from the one which is used (in the
    MATERIAL definition) the user is obliged to define the corresponding
    low-energy neutron cross sections or the run will be stopped (your case)
    - Materials in the low-energy neutron cross section file are identified
    by a name and/or by 3 numbers
    - If the user doesn't specify any identifier number, the correspondence
    with materials defined in the input (or pre-defined) is established with
    the first material in the file having that 'name'
    - Option LOW-MAT can override that correspondence
    - If n identifier numbers are provided (n=3D 1; 2; 3), the first =
    satisfying all the n given identifiers will be selected
    - (Note that it is possible to have more than one FLUKA material
    corresponding to the same low-energy neutron material (for instance two
    irons with different density)

    Besides, as for liquid hydrogen the case will be more tricky as this
    would require 'hydrogen' cross sections suitable for cryogenic
    temperature. The lowest you can currently find is:

    H Natural Hydrogen (1) 87K JEF-2.2 N HYDROGEN 1 -5 87

    thus, at 87K. Depending on your application that can however be not what
    you're looking for.

    For information only, currently a new extended neutron library is in
    development offering:
    - 260 groups (31 of which thermal)
    - processed at different temperatures and for different self-shielding
    - with more materials added in order to allow for additional point-wise
    - possible future inclusion of cryogenic temperatures

    hope this helps, cheers


    > -----Original Message-----
    > From:
    > [] On Behalf Of Olaf Hartmann
    > Sent: 06 December 2007 15:40
    > To:
    > Subject: xsec not found
    > Hi all,
    > actually I'm using FLAIR to control my FLUKA simulation. So I=20
    > took from the "Database" the material properties assigned to=20
    > H-LIQUID which should be liquid hydrogen. If I put H-LIQUID=20
    > as target material, I get the following message in the output file:
    > *** (n,p) proton production activated for Xsec mat. # 1 ***
    > **** Low energy neutron xsec not found for some media 4 5 ****
    > H-LIQUID
    > I thought as a workaround to use 'normal' hydrogen but with=20
    > increased density. Is there another way?
    > Cheers,
    > Olaf.

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