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GEF 2021/1.1

General description of fission observables.
Last update May 23, 2022. (Pre-saddle mass loss added to list-mode output.)

Short characterisation of GEF 2021/1.1:

Compared to GEF 2020/1.2 there are two major modifications:
1. The description of the mass yields in the pre-actinides, especially asymmetric fission of nuclei around mercury, lead has been made more consistent with a unique parameter set, without using locally adjusted parameters.
2. A modified concept has been introduced to construct a new composite formula of the nuclear level density.
    a) The low-energy part is still described by the empirical constant-temperature systematics of von Egidy and Bucuresu. This is a very solid empirical information.
    b) The high-energy part is still described by the Fermi-gas formula of independent Fermions, based on a fictive macroscopic ground state. This is a rather well established theoretical expectation. However, an exponentially decreasing influence, originally introduced by Ignatuyk et al. to reflect the influence of shell effects, is interpreted to represent the E* depencence of the collective enhancement, in addition. (The same E* dependence for both contributions is assumed, since the E* dependence of the collective enhancement is not well known.) The magnitude of this exponentially decreasing contribution is adjusted by the condition that the level densities of the low-energy part and the high-energy part match at the transition energy. This way, the transition energy is not determined any more by the technical matching condition, as in the Gilbert-Cameron composite formula, but it can be adjusted to the critical nuclear pairing energy from theoretical models or, eventually from other experimental observables. Moreover, there is room for the influence of collective enhancement, which is not taken into account in the Gilbert-Cameron matching condition, even if the shell effect is considered. (A more detailed discussion is in preparation.) 

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.

An extended version of GEF-2021/1.1 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

Source files (Released Dec. 3, 2021)

FORTRAN version

Source files (Released Dec. 3, 2021.) Please inform us, when you encounter problems!