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LOW-MAT


    Sets the correspondence between FLUKA materials and low-energy
    neutron cross sections

    See also LOW-NEUT

     
WHAT(1)
= number or name 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, Note 7, and explanation of
WHAT(5)
here 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:
1) 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. 2) 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: i) the low-energy neutron material desired is unique or is listed before any other material with the same name in list 10} and ii) that name is the same as one in the FLUKA list (see 5}) or as given by a MATERIAL option and iii) there is only one FLUKA material associated with that low-energy neutron material 3) On the other hand, the option IS REQUIRED in any one of the following cases: i) 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 ii) The FLUKA name is different from the name of the low-energy neutron material or iii) 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. 4) (NOT IMPLEMENTED!) 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! Example (number based):
*...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+...
MATERIAL 6. 0.0 2.000 6. 0.0 0. CARBON MATERIAL 6. 0.0 1.700 15. 0.0 0. GRAPHITE MATERIAL 6. 0.0 3.520 16. 0.0 0. DIAMOND LOW-MAT 15.0 6. -3. 296. 0.0 0. CARBON LOW-MAT 16.0 6. -2. 296. 0.0 0. CARBON
* We have three materials with the same atomic composition, but different
* density (amorphous carbon, graphite and diamond). Graphite is declared as
* having the cross section of Graphite bound natural Carbon, while diamond
* is declared as having the same low-energy neutron cross section as Free Gas
* Carbon.
The same example, name based:
*...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+...
MATERIAL 6. 0.0 2.000 0.0 0.0 0. CARBON MATERIAL 6. 0.0 1.700 0.0 0.0 0. GRAPHITE MATERIAL 6. 0.0 3.520 0.0 0.0 0. DIAMOND LOW-MAT GRAPHITE 6. -3. 296. 0.0 0. CARBON LOW-MAT DIAMOND 6. -2. 296. 0.0 0. CARBON

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