Re: Thermal and epithermal neutrons

From: Stefan Roesler (sroesler@mail.cern.ch)
Date: Thu May 17 2007 - 22:15:48 CEST

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    Dear Alfred,

    There are low-energy neutron cross section data sets available in FLUKA
    which take into account molecular bindings. The cross section data set has
    to be associated with the material by the card LOW-MAT.

    The following cross section data set list has been copied from the Manual,
    Chapter 10. You would have to specify the data set giving the Identifiers
    in the LOW-MAT card.

           Material Temp. Origin RN Name Identifiers Gam
        H H2O bound nat. Hydrogen (1) 293K JEF-2.2 N HYDROGEN 1 -2 293 Y
        H CH2 bound nat. Hydrogen (1) 293K JEF-2.2 N HYDROGEN 1 -3 293 Y
        H Bound nat. Hydrogen (1) 293K JEF-2.2 N HYDROGEN 1 -4 293 Y
        H Free natural Hydrogen (1) 293K JEF-2.2 N HYDROGEN 1 -5 293 Y
       1H H2O bound Hydrogen 1 293K JEF-2.2 N HYDROG-1 1 +1 293 Y
       1H CH2 bound Hydrogen 1 293K JEF-2.2 N HYDROG-1 1 +11 293 Y
       1H bound Hydrogen 1 293K JEF-2.2 N HYDROG-1 1 +21 293 Y
       1H Free Hydrogen 1 293K JEF-2.2 N HYDROG-1 1 +31 293 Y
        H H2O bound nat. Hydrogen (1) 87K JEF-2.2 N HYDROGEN 1 -2 87 Y

    Hope this helps,

    Best regards
    Stefan

    On Thu, 17 May 2007, Tang, Alfred wrote:

    > Dear FLUKA experts,
    > I know that FLUKA has a very good reputation in neutron simulations down
    > to the thermal neutron regime (<1eV). In the case of complex materials
    > such as hydrogen rich compounds, my understanding is that the chemical
    > bindings of the molecules affect neutron transport because of the
    > rotation and vibration of the molecules. MCNPX deals with chemical
    > binding below 2eV (epithermal neutron regime) by letting the
    > S(\alpha,\beta) treatment take over the free atom model. It seems that
    > FLUKA does not ask for information about the chemical formula of the
    > molecule nor specify any S(\alpha,\beta) treatment. Shall I assume that
    > FLUKA also uses a free atom model above 2eV? My real question is "How
    > does FLUKA simulate neutrons below 2eV?"
    > Regards,
    > Alfred
    >
    >
    > **************************************
    > Alfred Tang
    > Physics Department
    > Kansas State University
    > 13 Cardwell Hall
    > Manhattan, KS 66506
    >
    > (785) 532-1699
    >
    > http://www.phys.ksu.edu/personal/atang
    >
    >
    > 

    -- 
___________________________________
Stefan Roesler
CERN, SC/RP
CH-1211 Geneva 23
Switzerland
Phone:  +41-22-7679891
Fax:    +41-22-7669639
E-mail: Stefan.Roesler@cern.ch
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