The high precision neutron models discussed in the previous section
depend on an evaluated neutron data library (G4NDL) for cross sections,
angular distributions and final state information.  However the library
is not complete because there are no data for several key elements.
In order to use the high precision models, users must develop their
detectors using only elements which exist in the library.  In order to
avoid this difficulty, alternative models were developed which use 
the high precision models when data are found in the library, but 
use the low energy parameterized neutron models when data are missing.

The alternative models cover the same types of interaction as the 
originals, that is elastic and inelastic scattering, capture and fission.
Because the low energy parameterized part of the models is independent
of G4NDL, results will not be as precise as they would be if the 
relevant data existed. 

