Joint Evaluated Fission and Fusion (JEFF) Library

The NEA GitLab is used to rigorously version control all fundamental evaluated nuclear data files and, in some cases, more elementary information such as input data for nuclear reaction modelling codes, resonance or other nuclear model parameters, and other output data that is serialised by evaluated file preparation tools.

Accessing the JEFF evaluated and processed data

These pages provide links to evaluated and processed data files that are developed on the NEA GitLab. Public links are provided for certain data types and are available from the following pages. Wherever content is restricted, it is hosted on GitLab repositories and/or data pipelines executed on the NEA local datacentre.

JEFF-4.0

The JEFF-4.0 nuclear data library combines the available experimental and theoretical knowledge of nuclear reactions and nuclear decay in standard format nuclear data files that ensure serving a wide user community. JEFF-4.0 aims at being a general-purpose library suitable not only in the nuclear energy and nuclear fusion domains but also for domains such as space and earth exploration, medical isotope production and nuclear science.

The main emphasis of development of the JEFF-4.0 library is on neutron-induced reaction data, but the library also incorporates significant updates on the fission yields, the proton-induced reaction data and the decay data. The library contents are described in detail at the JEFF-4.0 release webpage. The JEFF-4.0 library was released in June 2025.

Latest official release

The JEFF-4.0 nuclear data library is the latest official release from the JEFF project.

Older JEFF data libraries

These libraries have been released between 1986 and 2017 and while commonly used around the world, the JEFF project has superseded these data with the version 4.0 official release. Access to the data is provided from these pages to secure archives at the NEA Data Bank.

Other evaluated nuclear data libraries

The JEFF project collaborates with other worldwide evaluation initiatives, including national projects and international networks co-ordinated by the IAEA. Several data sets are included in the official JEFF releases and these reflect the best performing data, from the perspective of the JEFF Co-ordination Group, from around the world.

Several libraries are stored at the Data Bank besides the JEFF data and are processed through the NEA GitLab data pipelines.

Note

Please contact data@oecd-nea.org for more information.