From: Alberto Fasso' (fasso@SLAC.Stanford.EDU)
Date: Thu Oct 18 2007 - 11:30:25 CEST
Dear Jason,
I always recommend to use LOW-MAT only when it is strictly necessary,
and that doesn't happen very often. In principle it should not hurt in any
case,
provided it is used in the correct way, but experience has shown that
many users tend to have problems with it.
Now, I know that FLAIR inserts systematically LOW-MAT cards which are not
needed, but I am trying to convince Vasilis Vlachoudis (author of FLAIR) to
modify this feature.
The manual is very clear on this point, so I copy here the relevant Note:
Option LOW-MAT should be avoided if it is not really necessary
(experience has shown that it is often misinterpreted by beginner
users). The option is NOT REQUIRED if the following 3 conditions
are all true:
1) the low-energy neutron material desired is unique or is
listed before any other material with the same name in
list 10}
and
2) that name is the same as one in the FLUKA list (see 5}) or as
given by a MATERIAL option
and
3) there is only one FLUKA material associated with that
low-energy neutron material
On the other hand, the option IS REQUIRED in any one of the
following cases:
1) there is more than one low-energy neutron material with
that name (this can happen because of data sets coming
from different sources, or corresponding to different
neutron temperatures, or concerning different isotopes, or
weighted on different spectra, etc), and the one desired
is not coming first in the list. In this case it is
sufficient to provide just as many identifiers as required
to remove ambiguity
or
2) The FLUKA name is different from the name of the
low-energy neutron material
or
3) There is more than one FLUKA material associated with the
given low-energy neutron material. This can happen for
instance when the same material is present with different
densities in different regions. In reality this is a
special case of 2) above, since to distinguish between the
different densities, different names must be used and one
at least will not be equal to the name of the
low-energy neutron material.
Alberto
On Wed, 17 Oct 2007, Jason Crawford wrote:
> Hello, I am having troubles using the LOW-NEUT/PART-THR/LOW-MAT cards.When
> I disable these cards my input runs fine, but when enabled, these cards
> are responsible for an output message, which reads:
>
> **** Fluka stopped in Lowset: undefined atomic density for the low en.
> xsec mat. corresponding to the Fluka comp. mat. n. 10 ****
>
> I have looked through past messages on the fluka discussion board to find
> out that this may be caused by my LOW-MAT card for Nitrogen, suggesting
> it should read:
> LOW-MAT NITROGEN 1.0 -2.0 ...
> (referencing the new code for Nitrogen, -2.0)
>
> After making sure my :LOW-MAT card for Nitrogen was correct my simulation
> still gave me the same error. Can this be explained? Can Someone help me
> find the solution?
-- 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
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