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GEF 2019/1.1

General description of fission observables. Released February 4, 2019.
Update: February 11, 2019 (minor revisions).
Update: February 17, 2019 (multi-chance fission supported for energy distribution from file).
Update: April 15, 2019 (output of fission probabilities for E*-distribution from file with multi-chance fission).
Update: May 5, 2019 (extended output of list-mode data).
Last update: June 6, 2019 (revised list-mode output, excitation energy of higher-chance fission revised).

Short characterisation of GEF 2019/1.1: The parameters of GEF were re-adjusted, using some very accurate mass yields measured at LOHENGRIN and sets of independent yields from JEFF 3.3. An apparent influence of the N=50 shell on the charge polarization was introduced. The calculations of the fission probability and of the gamma spectrum were revised. Calculations outside the recommended validity range of GEF (in A, Z or E* of the fissioning system) have been made possible with a warning.

Properties of GEF 2019/1.1: GEF 2019/1.1 gives a good description of different kind of fission data for a large variety of systems. Tests are still going on. Therefore, some minor modification may still be applied.
Very accurately measured fission yields of specific systems are better reproduced with locally adjusted parameters. (See this table for the values of the local parameters.) The adjustment was performed for different groups of elements, not for individual fissioning systems. (It is assumed that this adjustement refers to weak shells, which could not be taken into account in the standard formalism of GEF.) If most realistic results, also of other fission quantitites, are demanded, it is recommended to use locally adjusted parameters.
The mass distribution from GEF can be compared with empirical data from the ENDF/B-VII, JEFF 3.1.1, JEFF 3.3 evaluations or from experiments at LOHENGRIN in a plot (see example below), if available. This table lists the data that are stored in GEF. (In the moment, the Windows version of GEF has only access to ENDF/B-VII and JEFF 3.3.)

Mass yields of U235T in comparison with JEFF 3.3

The mass distribution of 235U(nth,f) from GEF-2019/1.1 (red points) in comparison with the JEFF 3.3 evalution (black symbols with error bars). The calculated contributions from different fission channels are traced in green. 10 million events have been calculated. (If the figure is not shown, pllease use this link.)

An extended version of GEF-2019/1.1 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>t_online.de). 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 runs also on OS X (e) with Wine (d). 

a) FreeBASIC is available from http://www.freebasic.net/ 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 http://www.justbasic.com/ with no cost.
d) Wine is a windows compatibility layer for Linux and Mac OS X (http://www.winehq.org/).
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:

GUI for GEF on Windows

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-assisted 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