As explained above, for thick target measurements, the connection between the high-energy INC codes and the low energy is usually done at neutron energies of 20 MeV. However, at such low energies, the INC codes are not expected to perform well. Work is in progress to extend the low-energy codes to much higher energies, typically 150 MeV. To that end, the MCNPX code of Los Alamos [114] uses pre-equilibrium models to generate data files specific to the different nuclear species. The approach of the Bruyeres le Chatel group is, rather, to use an optical model calculation [115]. Figure 6.7, prepared by Koning, compares an experimental neutron spectrum, as observed at JAERI [116], to the traditional calculation and to a calculation incorporating the Bruyeres le Chatel approach. The improvement is striking. Calculations using the new library prepared by Los Alamos give an agreement with experiment similar to that obtained with the Bruyeres le Chatel method. In particular one can see that the strong discontinuity at 20 MeV displayed by the traditional calculation, which is due to the inaccuracy of the INC model, is completely removed in the new calculations.