NJOY is a nuclear data processing code developed at Los Alamos National Laboratory.

NJOY21—NJOY for the 21st Century

NJOY21 is the next generation of NJOY designed to modernize nuclear data processing including the ability to process nuclear data from multiple data formats. NJOY21 has been released as open-source software without any export control restrictions. NJOY21 can be found on GitHub.

The goals for NJOY21 can be found at the Vision, Mission, Goals page.


NJOY2016 is the latest version of the Fortran-based code. New with NJOY2016 is that it is being distributed as open-source software, without any export control restriction. NJOY2016 can be found on GitHub.


NJOY was originally developed by Bob MacFarlane in the 1970s at Los Alamos National Laboratory. Skip Kahler was the main developer from the mid-2000s until 2016 when Jeremy Lloyd Conlin became the primary developer.


NJOY has benefited greatly from contributions from collaborators from around the world. With the open source availability of NJOY, we are actively encouraging collaboration from developers everywhere. For more information on contributing to NJOY development, please see our Developers Guide.