Re: Problem using different materials

From: Paola Sala (
Date: Wed May 02 2007 - 16:39:39 CEST

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    The problem with your input is that Uranium is not a fluka pre-defined
    material ( the list of pre-def is in the fluka manual, or in the menu of
    the ASSIGNMAT card in FLAIR, for instance),
    and there is not a low-energy neutron data set for URANIUM. You can see
    the message at the end of your geomneut_u001.out file:

      **** Low energy neutron xsec not found for some media 0 1 ****

    Low energy neutron cross sections are available for the separate Uranium
    isotopes, not for the natural composition. Again, to have the list of
    the available low-energy neutron cross section you can have a look in
    the manual, section 10} Low-energy neutrons in FLUKA
    For your target, you should define URANIUM as a compound made of the
    different isotopes. For instance:

    MATERIAL 92.0 235.0439 18.95 235.0 235-U
    MATERIAL 92.0 238.0508 18.95 238.0 238-U
    COMPOUND 0.007 235-U 0.993 238-U URANIUM

    In this way one defines uranium as 99.3 % 238-U and 0.7% 235 U . The
    materials 235-U and 238-U are automatically recognized for what concerns
    the low energy neutrons.
    Hope this helps

    On Wed, 2007-05-02 at 15:07 +0200, Feracci Vincent wrote:
    > Hi,
    > I am working on a simulation of an uranium target bombarded by
    > neutrons and being quite new with FLUKA I can't seem to use other
    > materials than those predefined by FLUKA:
    > In this early simulation I am bombarding a cylindric target with a
    > 40 MeV neutron beam. The simulation works fine with a carbon target but
    > as soon as I try using Uranium or any other material FLUKA doesn't
    > generate anything but a log file and rangeomneut_u001 (geomneut_u being
    > my input file).
    > I have attached geomneut_u.inp which is my file with an uranium
    > target which doesn't work and geomneut_c.inp which is the same file with
    > a carbon target and which works okay.
    > I use Flair V 0.4 to run my simulations, could that be a source of
    > problem?
    > Would somebody be kind enough to tell me what's wrong with my simulation?
    > Thank you very much for your attention,
    > Vincent Feracci

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