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A "simple" python interface to the EXFOR library

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x4i3 - The EXFOR Interface [for Python 3]

This package x4i3 is a fork of the original x4i developed by David A. Brown (LLNL, Livermore CA, 94550). This pure python software acts as an interface to Experimental Nuclear Reaction Data (EXFOR) that the International Atomic Energy Agency (IAEA) actively maintains.

The database resembles a collection of experimental and evaluated nuclear data files in the EXFOR format (*.x4), a structured markup language. The mark-up language is quite complex and the data has legacy issues, such as data sets entered by hand or issues with the strict alignment criteria of FORTRAN-era punch cards. The documentation by David A. Brown describes a few basics of the format. Please use this documentation, the references therein and the other files in the doc folder. Please also cite the papers about the database if you use these data in your research.

The main purpose of this fork is to ensure that such a valuable and complex tool does stays available. Also, the original link for this code is dead and Python 2 is deprecated. As a standalone pure Python package on pip, it may cure derived works from a potential GPL infection.

Latest release 1.2.0

Update to EXFOR database version dated 2021/03/08.


This fork emerged originally in 2016 when we tried to benchmark current photo-nuclear interaction codes against experimental data in a project related to Ultra-High Energy Cosmic Rays. One paper that came out has a quite useful plot (Figure 1). Actually, this figure is an interactive matplotlib application that used the original x4i as a backend. When a box is clicked x4i gathers experimental data from EXFOR, applies some filtering and visualizes the data against pre-computed model predictions.


Nothing very useful yet. To check out if the installation is successful, try:

    python examples/ --data -s 10504002

It should print some fission cross section to stdout.


..are welcome. Also feel free to say hi since I don't know if there is a community who may find this interface useful.

Currently there is no development goals beyond basic maintenance.


  • ~1 GB of hard drive space


pip install x4i3

Note that on first import ~600MB will be downloaded and 22k files will be decompressed to the data directory.

Support tools

To reduce the weight of this package, the database management tools have been moved to a different project x4i3_tools since these are for advanced users anyways.


There is currently no separate documentation for x4i3. Please use the original documentation. The installation instruction are not valid anymore. There is a detailed but auto-generated API-doc documentation. Untar and enjoy the index.html if you need this.


David A. Brown (LLNL) (x4i)

Anatoli Fedynitch (x4i3)

Copyright and license

This code is distributed under the GNU General Public License (GPLv2) (see LICENSE) without any warranty or guaranty. The full disclaimer and license information is located in the LICENSE. Very unfortunately, the original code is GPLv2 infecting in a nontransparent way all derived works such as this. Be warned!

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