tokens: The displacement damage shall be expressed either by : - Displacement damage equivalent particle fluence ( DDEF ) for mono - energetic spectra , NOTE For example , damage induced as a function of fluence from 10 MeV protons , 1 MeV neutrons or 1 MeV electrons , identified by DDEF(particle , energy , material ) . - The non - ionising energy loss ( NIEL ) dose or ( total ) non - ionising dose ( ( T)NID ) , i.e. the energy deposition in a material per unit mass by radiation through displacements . NOTE 1 This is distinctly different to TID for which energy is deposited as ionisation and excitation . NOTE 2 Units of TNID are Gy(material ) or rad(material ) , but for space radiation effects analysis , MeV / g is more commonly used to avoid confusion with TID - related quantities .