i hope someone can give me the exact code,thanks!
There is Geant4 Physics List with HP (high precision neutrons) sub-package. Data are based on neutron data bases.
The ENDF 8.0 and other libraries in Geant4 format are available at https://www-nds.iaea.org/geant4/ . They can be plugged in by pointing the G4NEUTRONHP env. variable to them. Make sure to follow the README file instructions.