From: Alberto Fasso' (fasso@SLAC.Stanford.EDU)
Date: Tue Jul 24 2007 - 11:15:52 CEST
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 group
1 1.0000 1.0000 1.0000 73 72
2 1.0000 1.0000 1.0000 73 72
3 1.0000 1.0000 1.0000 65 72
4 1.0000 1.0000 1.0000 65 72
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, which means
7.3375E-09 GeV (see energy group structure in the Manual).
On Mon, 23 Jul 2007, firstname.lastname@example.org wrote:
> 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,
-- Alberto Fasso` SLAC-RP, MS 48, 2575 Sand Hill Road, Menlo Park CA 94025 Phone: (1 650) 926 4762 Fax: (1 650) 926 3569 email@example.com
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