Description of Fission
Description of the
The model has been developed with the aim to provide dedicated nuclear
data for applications in nuclear technology and engineering. The code
considers spontaneous fission and fission up to an excitation energy of
about 100 MeV (including multi-chance fission) for a wide range of
nuclei from polonium to seaborgium. The development of GEF has been
supported by the European Union in the framework of the EFNUDAT project
(http://www.efnudat.eu/), of the
ERINDA project (http://www.erinda.org/), of the CHANDA project
(http://www.chanda-nd.eu/) and, during the years 2010 - 2016, by the
OECD Nuclear Energy Agency. A
detailed description of the physics of the code is given in the JEFF-Report 24
of the Nuclear-Energy Agency of the OECD.
Executables of the GEF code for Windows[a] and Linux are
available. They are easy to use: Just download the ZIP file,
extract the files and
run GEF.bat (Windows [a]) or ./GEF (Linux) in a command window on your
computer! The file README.txt
contains further information.
[a] Windows is either a registered trademark or a trademark of
Corporation in the United States and/or other countries.
Empirical fission-fragment Z and mass distributions compared with GEF
ingredients of the model
- The mass division and the charge polarization are
assuming a statistical population of states in the fission valleys at
freeze-out. The freeze-out time considers the influence of fission
dynamics and is not the same for the different collective variables.
- The separability principle  governs the interplay of
macroscopic and microscopic effects.
- Five fission channels are considered. The strengths of the
in the fission valleys are identical for all fissioning systems. The
mean positions of the heavy fragments in the asymmetric fission
channels are essentially constant in atomic number, as suggested by
experimental data . (Read
- The stiffness of the macroscopic potential with respect to
asymmetry is deduced from the widths of measured mass distributions .
- The excitation-energy-sorting mechanism [4,5,6,7]
prompt neutron yields and the odd-even effect in fission-fragment
yields of even-Z and odd-Z systems. (Read
- Neutron evaporation is calculated with a Monte-Carlo
code using level densities from empirical systematics  and binding
energies with theoretical shell effects  with gamma competition
 Experimental evidence for the separability of
and fragment properties in fission, K.-H. Schmidt, A. Kelic,
Ricciardi, Europh. Lett. 83 (2008) 32001
 Nuclear-fission studies with relativistic secondary
analysis of fission channels, C. Boeckstiegel et
Phys. A 802 (2008) 12
 Shell effects in the symmetric-modal fission of
nuclei, S. I. Mulgin, K.-H. Schmidt, A. Grewe, S. V. Zhdanov,
Phys. A 640 (1998) 375
 Entropy-driven excitation-energy sorting in superfluid
K.-H. Schmidt, B. Jurado, Phys. Rev. Lett. 104 (2010) 212501
 Influence of complete energy sorting on the
characteristics of the odd-even effect in fission-fragment element
distributions, B. Jurado, K.-H. Schmidt, J. Phys. G: Nucl.
Part. Phys. 42 (2015) 055101
 Thermodynamics of nuclei in thermal contact,
B. Jurado, Phys. Rev. C 82 (2011) 014607
 Final excitation energy of fission fragments,
Schmidt, B. Jurado, Phys. Rev. C 83 (2011) 061601(R)
 Inconsistencies in the description of pairing effects in
nuclear level densities, Phys. Rev. C 86 (2012) 044322
 Global view on
fission observables - new insights and new puzzles, K.-H.
Schmidt, B. Jurado, Phys. Proc. 31 (2012) 147
 General description of fission
observables - GEF model, K.-H. Schmidt, B.
Jurado, Ch. Amouroux, JEFF-Report 24, Data Bank, Nuclear-Energy Agency,
 Revealing hidden
regularities with a general approach to fission, K.-H.
Schmidt, B. Jurado, Eur. Phys. J. A 51 (2015) 176
description of fission observables: GEF model code, K.-H.
Schmidt, B. Jurado, C. Amouroux, C. Schmitt, Nucl. Data Sheets 131
 Influence of
complete energy sorting on the characteristics of the odd-even effect
in fission-fragment element distributions, B. Jurado,
K.-H. Schmidt, J. Phys. G: Nucl. Part. Phys. 42 (2015) 055101 [arXiv:
 Review on the
progress in nuclear fission - experimental methods and theoretical
descriptions, K.-H. Schmidt, B. Jurado, Rep. Progr. Phys.
81 (2018) 106301
Flowchart of GEF
Flowchart of the GEF code. (If the chart is not shown, please use this link .)
input of GEF
Z and A of fissioning nucleus or target
Excitation mode and excitation energy (eventually energy distribution)
on output of GEF
Contributions of fission chances (multi-chance fission)
Relative yields of fission channels
Element-yield distribution *)
Isotonic-yield distribution (pre- and post-neutron)
Isobaric-yield distribution (pre-and post-neutron) *)
Mass-chain yields (pre- and post-neutron) *)
Fragment angular-momentum distributions (for every nuclide)
Relative independent isomeric yields
Fragment total kinetic energy (pre- and post-neutron)
Energies and directions of pre- and post-scission prompt neutrons
Many more quantities are internally calculated and may be
An extended version of
includes delayed processes (output of delayed-neutron multiplicities,
delayed-neutron emitters, cumulative fission-fragment yields in ENDF
format etc.) is available on demand.
*) Uncertainties of fission yields from perturbed-parameter calculations
and covariences of fission-fragment yields.
DownloadGEF code, Version 2021.1.1 (Release: June 2, 2021, GEFSUB.FOR last update May 23, 2022)
GEF code, Version 2020,1.2 (Release: December 4, 2020, last update January 4, 2021)
GEF code, Version 2020,1.1 (Release: July 30, 2020, last update September 18, 2020)
GEF code, Version 2019/1.3 (Release: February 2, 2020; last update April 27, 2020)
GEF code, Version 2019/1.2 (Release: September 4, 2019; last update April 9, 2020)
GEF code, Version 2019/1.1
(Release: February 5, 2019; last modification June 6, 2019)
GEF code. Version 2018/1.1
(Release: June 21, 2018)
GEF code, Version 2017/1.2
(Release: October 18, 2017; last modification January 30, 2018)
GEF code, Version 2017/1.1
(Release: September 24, 2017)
GEF code, Version 2016/1.2
(Release: November 26, 2016)
GEF code, Version 2016/1.1
(Release: October 14, 2016)
GEF code, Version 2015/2.2
(Release: September 22, 2015, numerical stability improved on September
technical modifications on October 3, November
26, 2015, April 11,
April 29, May 29, July 2, and Sept. 7, 2016.)
(Description of non-statistical prompt gamma energies with a new VMI
Improved description of fission chances and fission-fragment
distributions for highly excited systems.
Improved description of fragment distributions for light fissioning
systems (Z = 76 to 90).
Note: GEF Version 2015/2.1 should not be used any more.
GEF code, Version 2015/1.1
(Release: January 2, 2015, numerical stability improved on September
(Extended output options, covariances between results of different
GEF code, Version 2014/2.1
(March 25, 2014)
(New global parameter set, new systematics of fission barriers)
GEF code, Version 2014/1.2
(January 25, 2014)
(Modified description of multi-chance fission.)
GEF code, Version 2014/1.1
(January 4, 2014)
(New global parameter set, modifications for better description of
GEF code, Version 2013/2.2
(December 6, 2013)
(Even odd effect in fission-fragment neutron-number distribution
Mass distribution at high excitation energies revised.
Prompt-neutron emission improved.
Output of pre-fission and post-scission neutrons extended.
Influence of temperature dependent shape oscillations on
prompt-neutron emission considered.
Fission-gamma competition refined.
New global parameter set.
Multi-chance fission modified.
Spurious even-odd effect in fission probabilities removed.)
Supplemental and help information
information for reading a covariance or correlation matrix from the GEF
The covarience or correlation matrix of nuclide yields (specified in Z and A) is listed in
a special format.
The program ReadCorr is provided that interprets the data structure and lists the
4-dimensional (Z1, A1, Z2, A2) coordinates and the corresponding matrix
values. This program may help you to read the matrices from the GEF
output with your own software.
- Guide for the
production of covariance and correlation matrices with GEF
The technical parameters for the production of
(and the corresponding uncertainties), covariances and correlations are
discussed, and their influence on the qualitiy of the data is
and demonstrated this report.
Authors: Beatriz Jurado (jurado (at) cenbg.in2p3.fr)
Karl-Heinz Schmidt (schmidt-erzhausen (at) t-online.de).