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Joint Evaluated Fission and Fusion (JEFF) Library version 3.1

The Joint Evaluated Fission and Fusion File (JEFF) is an evaluated library produced via an international collaboration of Data Bank member countries co-ordinated under the auspices of the NEA Data Bank. The JEFF-3.1 release contains neutron reaction data, thermal neutron scattering law data, and incident proton data for transport calculations, as well as special purpose files with radioactive decay data, fission yields data, and activation data. JEFF-3.1 combines the efforts of the JEFF and EFF/EAF working groups who have contributed to this combined fission and fusion file.

Superseded library

Please note that this is a superseded library that was approved for formal release but has been replaced with a newer official library version.


The complete set of data, including incident-neutron files, thermal scattering data, radioactive decay data, fission yields and activation data are available online at:



NEA (2006), "The JEFF-3.1 Nuclear Data Library", JEFF Report 21, NEA No. 6190, ISBN : 92-64-02314-3, Available online.