GEF 2017/1.2

General description of fission observables. Released October 18, 2017.
Modification October 23, 2017. (New set of model parameters. Note that this affects the results of the model!)
Modification October 30, 2017. (Spurious structure in pre-neutron yields at exact symmetry removed.)
Modification November 1, 2017. (New set of model parameters. Note that this affects the results of the model!)
Modification November 23, 2017. (Modified parameters for Z=38 shell. Affects the results for light systems!)
Modification November 24, 2017. (Sequence of energy values are now also allowed for input from file with options "GS" and "EB"; no change in the physics of the model.)
Modification November 27 - December 20, 2017. (Calculation of fission probabilities modified - new algorithm. Affects results of multi-chance fission.)
Modification Januray 20, 2018. (Optional scaling of variation of perturbed parameters introduced. Results of GEF are unchanged.)
Modification January 29, 2018. (Calculation of covariances/correlations between two different systems corrected. Results of GEF are unchanged.)
Modification January 30, 2018. (Model parameters slightly modified, better adjusted to independent yields of 235U(nth,f).)

Short characterisation of GEF 2017/1.2:  The November-23 version of GEF 2017/1.2 is the result of a careful re-adjustment of the model parameters, still with special care on the reproduction of the fission observables of 235U(nth,f) and a tentative description of systems in the Hg-Pb region. Because there were many substantial modifications with respect to GEF 2016/1.2, we are still checking "all corners" of the code. Therefore this GEF version should still be considered as "under development". When the new features are not needed, GEF 2016/1.2 may also be used as a stable alternative.

Properties of GEF 2017/1.2: GEF 2017/1.2 is the result of a new careful and comprehensive fit of the model parameters to experimental data. In particular, the mass distribution of 235U(nth,f), the system for which the most accurate data exist, was considered with special care. GEF 2017/1.2 replaces the preliminary version GEF 2017/1.1 that was the first which achieved an appreciably improved description of the mass-yield data for 235U(nth,f) by the replacement of the yield for A=129 by an alternative experiment (see figure below).
Less weight has been layed on a good description of spontaneous fission. In particular, the far-reaching tails of the super-asymmetric fission channel are underestimated by this version of the GEF model, because we could not find a consistent description that also reproduces the data of neutron-induced fission.
GEF 2017/1.2 provides also a tentative description of the mass yields in the mercury-lead region, e.g. the beta-delayed fission of 180Hg, the proton-induced fission of 201Tl and other systems in this region. In addition, the excitation-energy-dependent influence of shell effects on the symmetric fission channel has been reconsidered, leading to modifications of the TKE and of the mass-dependent prompt-neutron multiplicities.
Also the influence of pairing on the fission probabilties near the threshold has been re-considered.
Finally, an error in the calculation of the fission probability that appeared for nuclei with a strong ground-state shell effect has been corrected. This error appears in all previous GEF versions.

Mass distribution of 235U(nth,f)
The mass distribution of 235U(nth,f) from GEF-2017/1.2 (red points) in comparison with the ENDF/B-VII evalution (black symbols with error bars). The calculated contributions from different fission channels are traced in green. 10 million events have been calculated. The data point for A=129 is taken from H. Thierens, D. de Frenne, E. Jacobs, A. de Clercq, P. D'Hondt, A.J. Deruytter , Nucl. Instrum. 134 (1976) 299-308.

An extended version of GEF-2017/1.2 that includes delayed processes (output of delayed-neutron multiplicities, delayed-neutron emitters, cumulative fission-fragment yields in ENDF format) is available on demand.
It provides also an option for producing random files of fission-fragment yields in ENDF format.

We are happy about any feed-back (mail to schmidt-erzhausen<at> This helps to correct errors, to improve the quality of the model and to better respond to the needs and preferences of the users.

Use of the GEF code is subject to the GNU GENERAL PUBLIC LICENSE agreement that you find here: <License>.

Stand-alone version (Monte-Carlo method)

The stand-alone version of the GEF code is written in FreeBASIC (a). The FreeBASIC compiler produces binary code from the same source on Windows (b) and on Linux. The executable uses the C library.  For  the Windows version, a GUI is provided, written in JustBasic (c). The Windows version runs also on Linux with Wine (d).  The Windows version should also run on OS X (e) with Wine (d). (Did somebody try it?)

a) FreeBASIC is available from with no cost.
b) Windows is either a registered trademark or a trademark of Microsoft Corporation in the United States and/or other countries.
c) JustBasic is available from with no cost.
d) Wine is a windows compatibility layer for Linux and Mac OS X (
e) OS X is a trademark of Apple Inc., registered in the U.S. and other countries.

Quick start on Windows:

Quick start on Linux:

Windows version

Input mask of the graphical user interface:

Input maks of GEF GUI

For Windows and Linux

Complete package


Readme file (Technical information, list of relevant publications)
JEFF-Report 24, part I (Comprehensive documentation of the GEF model.)
JEFF-Report 24, part II (Technical information on the GEF code.)

Source (for Windows and Linux)

Source files


Input files for extended input options
Distribution of entrance energies (example)
List of input parameters (example)
See Readme file for more detailed information.
Data tables in XML format (example)
List-mode file (example)   (short sample of most complete event list)
Raw data for the multi-variate distribution of fission-fragment yields from calculations with perturbed parameters (example)
See Readme file for more detailed information.

You may consider using the Windows version of GEF on Linux with Wine in order to profit from the more comfortable input handling offered by the graphical user interface. This option may also solve problems of missing libraries under Linux.

Subroutine (Folding method) 

The subroutine aims for being used in combination with other nuclear-reaction codes. For a given fissioning nucleus with excitation energy E* and angular momentum I it calculates complete distributions of a number of fission observables before emission of prompt neutrons and prompt gamma radiation with the GEF model.


Technical description of the subroutine

FreeBASIC version

In preparation

FORTRAN version

In preparation