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!

5) See (15) for a complex example showing the use of MATERIAL, COMPOUND and LOW-MAT.

Example (number based):

 *...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+....8
 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.       -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....+....8
 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     GRAPHITE        6.       -3.      296.       0.0       0. CARBON
 LOW-MAT      DIAMOND        6.       -2.      296.       0.0       0. CARBON

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