sets the correspondence between FLUKA materials and low-energy
neutron cross-sections
(see also LOW-NEUT)
WHAT(1) = number of the FLUKA material, either taken from the list
of standard FLUKA materials (see 5}), or defined via
a MATERIAL option.
No default!
WHAT(2) = first numerical identifier of the corresponding
low-energy neutron material. Not used if = 0.0
WHAT(3) = second numerical identifier of the corresponding low-energy neutron
material. Not used if = 0.0
WHAT(4) = third numerical identifier of the corresponding low-energy neutron
material. Not used if = 0.0
WHAT(5) = compound material if > 0. This applies only to pre-mixed
low-energy neutron compound materials, which could
possibly be available in the future; at the moment
however, none is yet available. (It would be allowed
anyway only if the corresponding FLUKA material is also a
compound).
Default: compound if the FLUKA material is a compound,
otherwise not.
WHAT(6) = atomic or molecular density (in atoms/(10**-24 cm3), or
number of atoms contained in a 1-cm long cylinder with
base 1 barn. To be used ONLY if referring to a pre-mixed
compound data set (see COMPOUND and note to WHAT(5) above)
Note that no such data set has been made available yet.
SDUM = name of the low-energy neutron material.
Default: same name as the FLUKA material.
Default (option LOW-MAT not given): correspondence between FLUKA
and low-energy neutron materials is by name; in case of
ambiguity the first material in the relevant list (see 10})
is chosen.
Notes:
Each material in the FLUKA low-energy neutron library (see 10})
is identified by an alphanumeric name (a string of <= 8 characters,
all in upper case), and by three integer numbers. Correspondence with
FLUKA materials (pre-defined or user-defined) is based on any
combination of name and zero or more identifiers. In case of
ambiguity, the first material in the list fulfilling the
combination is selected.
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.
If WHAT(5) is set > 0.0 because a pre-mixed compound
low-energy neutron material is used, average cross-sections
are used (as for instance in the MORSE code). Otherwise, if
each of the FLUKA elemental components has been associated
with one of the elemental low-energy neutron components
and the composition of the compound has been defined by a
COMPOUND option, low-energy neutron interactions will take
place randomly with each individual component, with the
appropriate probability.
It is however possible to have in the same run detailed
individual interactions at high energies and average
compound interactions for low-energy neutrons. But NOT
THE OTHER WAY AROUND!
See 15} for a complex example showing the use of
MATERIAL, COMPOUND and LOW-MAT.
Example 1:
*...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+...
MATERIAL 6. 12.011 2.000 6. 0.0 0. CARBON
MATERIAL 6. 12.011 1.700 15. 0.0 0. GRAPHITE
MATERIAL 6. 12.011 3.520 16. 0.0 0. DIAMOND
LOW-MAT 15.0 6. -2. 293. 0.0 0. CARBON
LOW-MAT 16.0 6. -2. 293. 0.0 0. CARBON
* We have three materials with the same atomic composition, but different
* density (amorphous carbon, graphite and diamond). Both graphite and
* diamond are declared as having the same low-energy neutron cross section
* as carbon.
Example 2:
*...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+...
MATERIAL 5. 10.811 2.34 5. 0.0 0. BORON
MATERIAL 26. 55.847 7.87 11. 0.0 0. IRON
MATERIAL 60. 144.24 7.01 13. 0.0 0. NEODYMIU
MATERIAL 0. 0. 7.40 20. 0.0 0. NDFEB
COMPOUND 2. 13. 14. 11. 1. 5. NDFEB
LOW-MAT 13.0 26. -2. 293. 0.0 0. IRON
* A permanent magnet is made of an alloy of iron, neodymium and boron.
* Nd cross sections are not available yet. Let us assume for the time being
* that it has the same low energy neutron cross section as iron.
