GEF     A General Description of Fission Observables

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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 (, of the
ERINDA project (, of the CHANDA project ( 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 Microsoft
Corporation in the United States and/or other countries.

Comparision of GEF with data
Empirical fission-fragment Z and mass distributions compared with GEF calculations.

Main ingredients of the model

[1] 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
[2] Nuclear-fission studies with relativistic secondary beams: analysis of fission channels, C. Boeckstiegel et al.,  Nucl. Phys. A 802 (2008) 12
[3] 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
[4] Entropy-driven excitation-energy sorting in superfluid fission dynamics,
K.-H. Schmidt, B. Jurado, Phys. Rev. Lett. 104 (2010) 212501
[5] 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
[6] Thermodynamics of nuclei in thermal contact, K.-H. Schmidt, B. Jurado, Phys. Rev. C 82 (2011) 014607
[7] Final excitation energy of fission fragments, K.-H. Schmidt, B. Jurado, Phys. Rev. C 83 (2011) 061601(R)
[8] Inconsistencies in the description of pairing effects in the nuclear level densities, Phys. Rev. C 86 (2012) 044322
[9] Global view on fission observables - new insights and new puzzles, K.-H. Schmidt, B. Jurado, Phys. Proc. 31 (2012) 147
[10] General description of fission observables - GEF model, K.-H. Schmidt, B. Jurado, Ch. Amouroux, JEFF-Report 24, Data Bank, Nuclear-Energy Agency, OECD, 2014
[11] Revealing hidden regularities with a general approach to fission, K.-H. Schmidt, B. Jurado, Eur. Phys. J. A 51 (2015) 176
[12] General description of fission observables: GEF model code, K.-H. Schmidt, B. Jurado, C. Amouroux, C. Schmitt, Nucl. Data Sheets 131 (2016) 107
[13] 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: 14411.4478]
[14] Review on the progress in nuclear fission - experimental methods and theoretical descriptions, K.-H. Schmidt, B. Jurado, Rep. Progr. Phys. 81 (2018) 106301
[15] Extensive study of the quality of fission yields from experiment, evaluation and GEF for antineutrino studies and applications, K.-H. Schmidt, M. Estienne, M. Fallot, S. Cormon, A. Cucoanes, T. Shiba, B. Jurado, K. Kern, Ch. Schmitt, Nucl. Data Sheets 173 (2021) 54
[16] Experimental evidence for common driving effects in low-energy fission from sublead to actinides, C. Schmitt, A. Lemasson, K.-H. Schmidt, A. Jhingan, S. Biswas, Y. H. Kim, D. Ramos, A. N. Andreyev, D. Curien, M. Ciemala, E. Clement, O. Dorvaux, B. De Canditiis, F. Didierjean, G. Duchene, J. Dudouet, J. Frankland, B. Jacquot, C. Raison, D. Ralet, B.-M. Retailleau, L. Stuttge, I. Tsekhanovich, Phys. Rev. Lett. 126 (2021) 132502
[17] Evidence for the general dominance of proton shells in low-energy fission, K. Mahata, C. Schmitt, Shilpi Gupta, A. Shrivastava, G. Scamps, K.-H. Schmidt, Phys. Lett. B 825 (2022) 136859
[18] Identifying and overcoming deficiencies of nuclear data on the fission of light actinides by use of the GEF code (Preprint: )

Flowchart of GEF

Flowchart of the GEF code

Flowchart of the GEF code.

Required input of GEF

Z and A of fissioning nucleus or target
Excitation mode and excitation energy (eventually energy distribution)
Output options

Quantities available 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
Prompt-gamma spectrum
Prompt-neutron spectrum
Neutron-multiplicity distribution
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.

An extended version of GEF that 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.


GEF code, version 2023.3.2  (Release: December 16, 2023, last update January 14, 2024)

GEF code, version 2023.3.1  (Release: November 13, 2023)

GEF code, version 2023.2.2 (Release: July 16, 2023, last update Sept. 5, 2023)

GEF code, version 2023.2.1 (Release: April 14, 2023)

GEF code, version 2023.1.2 (Release: March 11, 2023, last update March 15, 2023)

GEF code, Version 2023.1.1 (Release: January 12, 2023, last update March 7, 2023)

GEF 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 23, 2015,
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.)

Supplemental and help information

Authors: Beatriz Jurado (jurado (at)
            and Karl-Heinz Schmidt (schmidt-erzhausen (at)