From: Markus Brugger (Markus.Brugger@cern.ch)
Date: Thu Dec 06 2007 - 18:36:58 CET
Hi Olaf,
when using low-energy neutron transport you've to be careful how to
specify the material (name) and in what way it relates to the respective
low-energy neutron cross-sections available in FLUKA. In order to find
out what material corresponds to what 'name' or parameters, please check
the manual, e.g., directly at:
http://www.fluka.org/manual/sect/s096/text.html
In general the following rules apply:
- In most cases, option LOW-MAT is not needed (however not in your
case!)
- If a material name different from the one which is used (in the
MATERIAL definition) the user is obliged to define the corresponding
low-energy neutron cross sections or the run will be stopped (your case)
- Materials in the low-energy neutron cross section file are identified
by a name and/or by 3 numbers
- If the user doesn't specify any identifier number, the correspondence
with materials defined in the input (or pre-defined) is established with
the first material in the file having that 'name'
- Option LOW-MAT can override that correspondence
- If n identifier numbers are provided (n=3D 1; 2; 3), the first =
material
satisfying all the n given identifiers will be selected
- (Note that it is possible to have more than one FLUKA material
corresponding to the same low-energy neutron material (for instance two
irons with different density)
Besides, as for liquid hydrogen the case will be more tricky as this
would require 'hydrogen' cross sections suitable for cryogenic
temperature. The lowest you can currently find is:
H Natural Hydrogen (1) 87K JEF-2.2 N HYDROGEN 1 -5 87
Y
thus, at 87K. Depending on your application that can however be not what
you're looking for.
For information only, currently a new extended neutron library is in
development offering:
- 260 groups (31 of which thermal)
- processed at different temperatures and for different self-shielding
factors=20
- with more materials added in order to allow for additional point-wise
treatment
- possible future inclusion of cryogenic temperatures
hope this helps, cheers
Markus
=20
> -----Original Message-----
> From: owner-fluka-discuss@mi.infn.it=20
> [mailto:owner-fluka-discuss@mi.infn.it] On Behalf Of Olaf Hartmann
> Sent: 06 December 2007 15:40
> To: fluka-discuss@fluka.org
> Subject: xsec not found
>=20
> Hi all,
>=20
> actually I'm using FLAIR to control my FLUKA simulation. So I=20
> took from the "Database" the material properties assigned to=20
> H-LIQUID which should be liquid hydrogen. If I put H-LIQUID=20
> as target material, I get the following message in the output file:
>=20
>=20
> *** (n,p) proton production activated for Xsec mat. # 1 ***
> **** Low energy neutron xsec not found for some media 4 5 ****
> H-LIQUID
>=20
>=20
> I thought as a workaround to use 'normal' hydrogen but with=20
> increased density. Is there another way?
>=20
> Cheers,
> Olaf.
>=20
>=20
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