RE: neutron cut-off energy

From: Alberto Fasso' (fasso@SLAC.Stanford.EDU)
Date: Sat Oct 20 2007 - 18:10:28 CEST

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    Dear Mary,
    ETRACK is TOTAL energy (kinetic plus mass). That is why it is always larger
    than the neutron mass in energy (about 0.939 GeV). To get the kinetic
    energy, subtract (in double precision!) ETRACK - 0.93956563D0.
    You need to get a small difference between two large numbers, so please
    use all decimal figures.

    Kind regards,

    Alberto

    On Sat, 20 Oct 2007, me@marychin.org wrote:

    > Hi Alberto,
    >
    > I'm digging up an earlier query (attached inline below), which you explai=
    ned very nicely. Now I have a related question:
    >
    > I'm starting thermal neutrons in a sea of Li-6, and B-10. When I look at =
    the neutron energy (ETRACK) at the time of ICODE=3D300 collisions, the neut=
    ron energy is always always always 0.9396 GeV. Is this not the 'real cut-of=
    f'? Is it due to the two different neutron cut-offs?
    >
    > Many thanks,
    > mary
    >
    >
    > -------------------------------------------------------------------------=
    -------
    > From: Alberto Fasso' [mailto:fasso@slac.stanford.edu]
    > Sent: Tue 24-Jul-07 10:15
    > To: me@marychin.org
    > Cc: fluka-discuss@mi.infn.it
    > Subject: Re: neutron cut-off energy
    >
    >
    > Hi Mary,
    >
    > there are two neutron cut-offs in FLUKA. 1.960E-02GeV is the
    > cut-off for high-energy neutrons, below which the special
    > multigroup treatment starts. With the present version it cannot be
    > changed: it could be changed only when using a different library
    > for low-energy neutrons (one with a different maximum energy).
    > This cut-off is changed with PART-THR, but only when allowed
    > by the low-energy neutron library
    >
    > The second cut-off, which is changed with LOW-BIAS, is the
    > real cut-off. It is not expressed in energy, but as a neutron
    > group number. Look carefully in the output:
    >
    > The first cut-off is reported as follows:
    > Cut-off kinetic energy for NEUTRON transport: 1.960E-02 GeV
    >
    > And the second cut-off as follows: (here the group cut-off has been set
    > as 73 for regions 1 and 2 - which means no cut-off at all - and group 65
    > in regions 3 and 4)
    >
    > Region Particle importances RR factor Cut off N.A. =
    abs.
    > number Fluka part. EM part. Low en. n. group gro=
    up
    >
    > 1 1.0000 1.0000 1.0000 73 7=
    2
    > 2 1.0000 1.0000 1.0000 73 7=
    2
    > 3 1.0000 1.0000 1.0000 65 7=
    2
    > 4 1.0000 1.0000 1.0000 65 7=
    2
    >
    > Here the group cut-off has been set as 73 for regions 1 and 2 - which mea=
    ns no
    > cut-off at all - and group 65 in regions 3 and 4, which means
    > 7.3375E-09 GeV (see energy group structure in the Manual).
    >
    > Alberto
    >
    >
    >
    > On Mon, 23 Jul 2007, me@marychin.org wrote:
    >
    >> Hi.
    >>
    >> I need a lower neutron cut-off energy. The default 1.960E-02GeV is too h=
    igh
    >> for me. I tried changing LOW-BIAS and PART-THR but I still get 1.960E-02=
    GeV.
    >> Could someone please help?
    >>
    >> Many thanks,
    >> mary
    >>
    >>
    >
    > --
    > Alberto Fasso`
    > SLAC-RP, MS 48, 2575 Sand Hill Road, Menlo Park CA 94025
    > Phone: (1 650) 926 4762 Fax: (1 650) 926 3569
    > fasso@slac.stanford.edu
    >
    >

    --=20
    Alberto Fass=F2
    SLAC-RP, MS 48, 2575 Sand Hill Road, Menlo Park CA 94025
    Phone: (1 650) 926 4762 Fax: (1 650) 926 3569
    fasso@slac.stanford.edu
    --1334195030-1989714345-1192896090=3D:28146--


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