Joint Evaluated Fission and Fusion (JEFF) Library version 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 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.
The JEFF-4.0 nuclear data library is the result of a comprehensive project, involving several test library versions that underwent rigorous study by the experts involved in the JEFF project. The project evolution is documented at the JEFF Test Releases overview.
The JEFF-4.0 library and sub-libraries contents are described and provided below.
Neutron-induced cross sections evaluations
The neutron-induced reaction data of the JEFF-4.0 library differ on many counts from the JEFF-3.3 library. Major changes were made to the Major Actinides U-235, U-238 and Pu-239 in the resonance region and in the fast region, where new physics models were introduced. Updates were also implemented for Th-232 and U-233 of importance to the Th-U fuel cycle and the Minor Actinides U-236, Np-237, Np-238, Pu-238, Pu-240, Pu-241, Pu-242, Am-241, and Am-243 of interest to spent fuel management, reprocessing and waste transmutation scenarios.
Fission product data in the thermal and resolved resonance region were reviewed, updated, and integrated in the TENDL library and then adopted in JEFF-4.0, ensuring complete files performing well for fission energy and for fusion activation and decay heat applications. The same approach was applied for many structural materials, coolant, and absorbers.
Through a close collaboration, neutron-induced reaction data were optimized and adopted from the INDEN project. Furthermore, several files were adopted from JENDL-4.0, from JENDL-5.0 and from ENDF/B-VIII.1 when these were deemed better than what was available. Finally, whenever not already included in the library, the JEFF-4.0 library adopted the available files from the TENDL-2023 library, updated in August 2024 and partially adapted further with files from the TENDL-2025 beta release made available in February 2025.
| Release | Format | Code | Content | # files | Download |
|---|---|---|---|---|---|
| JEFF-4.0 | ENDF6 | - | Cross section evaluations (download all) | 593 |  |
| JEFF-4.0 | ENDF6 | - | Cross section evaluations (download all) | 2855 |  |
| JEFF-4.0 | ACE | NJOY2016.78 | Continuous-energy cross section data at 293.6, 300, 600, 900, 1200, 1500, 1800 K | 593 |  |
| JEFF-4.0 | PENDF0K | NJOY2016.78 | Pointwise cross section data at 0 K | 593 |  |
| JEFF-4.0 | HDF5 | NJOY2016.78 and OpenMC | Continuous-energy cross section data at 293.6, 300, 600, 900, 1200, 1500, 1800 K | 593 |  |
| JEFF-4.0 | GENDF-1102 | NJOY2016.78 and PREPRO | Groupwise cross section data | 593 |  |
Citation
Joint Evaluated Fission and Fusion Project. (2025). JEFF-4.0 Evaluated Data: neutron data [Data set]. OECD Nuclear Energy Agency. https://doi.org/10.82555/e9ajn-a3p20
Fission Yields (FY)
The JEFF-4.0 fission yields sub-library is the JEFF-3.3 fission yields sub-library with new evaluations of the U-233, U-235, Pu-239, and Pu-241 thermal neutron-induced fission yields. These four thermal neutron-induced fission yields were evaluated following a completely new methodology including new measurements at the Lohengrin spectrometer and a careful treatment of the full experimental database. The changes introduced in JEFF-4.0 sub-library have proven critical for improved burn-up calculations and spent fuel characterization.
| Release | Format | Content | # files | Download |
|---|---|---|---|---|
| JEFF-4.0 | ENDF6 | Neutron-induced Fission Product Yields | 1 |  |
| JEFF-4.0 | ENDF6 | Spontaneous Fission Product Yields | 1 |  |
Thermal Scattering Law (TSL)
The JEFF-4.0 sub-library for thermal-neutron scattering provides a comprehensive dataset including the thermal scattering data for the elements of 84 materials of which 24 in elemental form and 60 compounds. Special attention has been paid to key reactor materials, providing evaluations for U and O in UO2, Pu and O in PuO2, Th and O in ThO2, and Zircaloy (Zy4). The files in the JEFF-4.0 TSL sub-library are from different sources:
- 36 elements are from the JEFF project, with 16 files that are new compared to JEFF-3.3, updates in 6 files and a new evaluation for the important case of hydrogen in water (H in H2O).
- 31 elements from ENDF/B-VIII.1 library.
- 65 elements from the NJOY+NCrystal Library.
Detailed information about the JEFF-4.0 TSL evaluations is provided here.
| Release | Format | Content | # files | Download |
|---|---|---|---|---|
| JEFF-4.0 | ENDF6 | Thermal Scattering Law Evaluations (download all) | 132 |  |
| JEFF-4.0 | ACE | Continuous-energy cross section data at all temperatures available | 132 |  |
Availability of ACE TSL data
Please note that processed ACE files are provided for selected TSL evaluations (Be met, D in D2O, C in Graphite, H in CH2, H in H2O, H in ZrH, ZrH1.5 and ZrH2, O and U in UO2, Zr in ZrH1.5 and ZrH2). Access to the complete dataset is available upon request - please contact data@oecd-nea.org.
Decay data
The JEFF-4.0 sub-library for decay data is the JEFF-3.3 sub-library with new TAGS data for 8 radionuclides (Rb-93, Y-96, Y-96m, Y-99, Tc-103, Tc-108, I-138, and Cs-142). The Q-value has been updated in the Tc-99 evaluation as well as the EC/B- branching and decay radiation for Am-242.
| Release | Format | Content | # files | Download |
|---|---|---|---|---|
| JEFF-4.0 | ENDF6 | Radioactive decay data | 1 |  |
Proton data
The JEFF-4.0 sub-library for proton-induced reactions is the TENDL-2023 sub-library except for 288 stable nuclides for which a thorough review has been carried out comparing and selecting evaluations from TENDL-2023, JENDL-5 and ENDF/B-VIII.1 libraries. In addition, the PADF-2 activation data were integrated in the selected evaluations allowing for the best description of the available experimental data.
| Release | Format | Content | # files | Download |
|---|---|---|---|---|
| JEFF-4.0 | ENDF6 | Incident proton (download all) | 2855 |  |
| JEFF-4.0 | ENDF6 | Incident proton (stable targets) | 288 |  |
| JEFF-4.0 | ACE | Incident proton (stable targets) | 288 |  |
Alpha
The JEFF-4.0 sub-library for alpha-induced reactions is the TENDL-2023 sub-library with a new evaluation for Be-9 prepared in the frame of the JEFF project.
| Release | Format | Content | # files | Download |
|---|---|---|---|---|
| JEFF-4.0 | ENDF6 | Incident alpha | 2835 |  |
Photon
The JEFF-4.0 sub-library for photon-induced reactions adopts the TENDL-2023 sub-library.
| Release | Format | Content | # files | Download |
|---|---|---|---|---|
| JEFF-4.0 | ENDF6 | Incident photon | 2825 |  |
Deuteron
The JEFF-4.0 sub-library for deuteron-induced reactions adopts the TENDL-2023 sub-library.
| Release | Format | Content | # files | Download |
|---|---|---|---|---|
| JEFF-4.0 | ENDF6 | Incident deuteron | 2850 |  |
Triton
The JEFF-4.0 sub-library for triton-induced reactions adopts the TENDL-2023 sub-library.
| Release | Format | Content | # files | Download |
|---|---|---|---|---|
| JEFF-4.0 | ENDF6 | Incident triton | 2865 |  |
Helion
The JEFF-4.0 sub-library for helion-induced reactions adopts the TENDL-2023 sub-library.
| Release | Format | Content | # files | Download |
|---|---|---|---|---|
| JEFF-4.0 | ENDF6 | Incident helion | 2821 |  |
References
The official journal paper associated to the JEFF-4.0 library release is currently under preparation, and will be made available soon.
Contact
Contact us via data@oecd-nea.org