Description of Fission
Items on this page
Description of the model
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 heavy
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/) and 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
Main ingredients of the model
- The mass division and the charge polarization are calculated
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 shells
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 more.)
- The stiffness of the macroscopic potential with respect to mass
asymmetry is deduced from the widths of measured mass distributions .
- The excitation-energy-sorting mechanism [4,5,6,7] determines the
prompt neutron yields and the odd-even effect in fission-fragment
yields of even-Z and odd-Z systems. (Read more.)
- Neutron evaporation is calculated with a Monte-Carlo statistical
code using level densities from empirical systematics  and binding
energies with theoretical shell effects  with gamma competition
 Experimental evidence for the separability of compound-nucleus
and fragment properties in fission, K.-H. Schmidt, A. Kelic, M. V.
Ricciardi, Europh. Lett. 83 (2008) 32001
 Nuclear-fission studies with relativistic secondary beams:
analysis of fission channels, C. Boeckstiegel et al., Nucl.
Phys. A 802 (2008) 12
 Shell effects in the symmetric-modal fission of pre-actinide
nuclei, S. I. Mulgin, K.-H. Schmidt, A. Grewe, S. V. Zhdanov, Nucl.
Phys. A 640 (1998) 375
 Entropy-driven excitation-energy sorting in superfluid fission
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, K.-H. Schmidt,
B. Jurado, Phys. Rev. C 82 (2011) 014607
 Final excitation energy of fission fragments, K.-H.
Schmidt, B. Jurado, Phys. Rev. C 83 (2011) 061601(R)
 Inconsistencies in the description of pairing effects in the
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, OECD, 2014
Required 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 listed.
*) Uncertainties of fission yields from perturbed-parameter calculations
and covariences of fission-fragment yields.
DownloadGEF 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 model,
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 23, 2015)
(Extended output options, covariances between results of different systems.)
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 multi-chance fission.)
GEF code, Version 2013/2.2 (December 6, 2013)
(Even odd effect in fission-fragment neutron-number distribution revised.
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.)
Authors: Beatriz Jurado (jurado (at) cenbg.in2p3.fr)
Karl-Heinz Schmidt (schmidt-erzhausen (at) t-online.de).