Re: neutron cut-off energy

From: Anna Ferrari (
Date: Tue Jul 24 2007 - 11:04:13 CEST

  • Next message: Alberto Fasso': "Re: neutron cut-off energy"

     Hi Mary,

     just some suggestions.

     I suggest to you to read in the online FLUKA manual
     -> 10. Low energy neutrons in FLUKA.

     There you can find that the treatment of the low energy neutrons is
     performed in FLUKA by a multigroup algorithm. With this algorithm you can
     simulate neutrons with an energy structure of 72 groups. You can read
     there the limits of each group, the lowest one (neutron group 72) being
     1.0000E-14 GeV.
     The low energy neutron treatment is working by default in FLUKA in
     ~ all the sets of FLUKA defaults (please check your defaults). I think
     you should have this treatment activated.
     The boundary between the high energy transport and the multigroup
     treatment is 19.6 MeV.

     With the PART-THR card you just set the threshold for the neutron
     transport at high energy, so in the regime above 19.6 MeV.
     You can read in the manual note in the PART-THR page that is
     not recommended at all to set the neutron cut-off LOWER than the
     higher energy boundary of the first neutron group (19.6 MeV), because the
     results are unpredictable!

     Whith LOW-BIAS you can set a group cutoff in the low energy treatment.
     For example, if you put what(1)=60 you set the energy cutoff
     at the upper edge of the 60th group (61.442 eV). This must work!

     Hope it helps,


    On Mon, 23 Jul 2007, wrote:

    > Hi.
    > I need a lower neutron cut-off energy. The default 1.960E-02GeV is too high for me.
       I tried changing LOW-BIAS and PART-THR but I still get 1.960E-02GeV.
    Could someone please help?
    > Many thanks,
    > mary

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