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GEneral Fission model

GEF : A GEneral description of the Fission process

The model has been developed with the aim to provide dedicated nuclear data for applications in nuclear technology and engineering. The code treates 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 and the ERINDA projects and by the OECD Nuclear Energy Agency. A detailed description of the code is given in this report and in this article published in Nuclear Data Sheets.

The required input of GEF is :

  • Z and A of fissioning nucleus
  • Excitation mode and excitation energy

GEF calculates the folowing quantities :

  • 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

Other quantities are internally calculated and may be listed.

*) Uncertainties of fission yields from perturbed-parameter calculations and covariences of fission-fragment yields.

The executable and the source code of GEF can be downloaded below. They are easy to use : Just download the ZIP file, extract the files and run GEF.bat (Windows [1]) or ./GEF (Linux) in a command window on your computer ! The file Readme.txt contains further information.

Download (including copyright information and license.) :

— > Additional information on this version can be found here.

  • GEF-code, Version 2016/1.1 executables and source (October 14 2016) (Handling of multi-threading. Proton-induced fission up to Ep = 30 MeV supported. Neutron emission between saddle and scission added. New adjustment of model parameters. Gamma spectra with condition on fragment mass. Uncertainties available for more fission observables, including the uncertainty due to the fission fragment angular momenta.)

— > Additional information on this version can be found here.

  • GEF-code, Version 2015/2.2, executables and source (September 7 2016) (Overflow problems for large event numbers and in removed. Numerical stability improved. Calculation of covariances between different systems corrected. 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). Prompt-neutron spectrum with variable binsize added in folder "/out". Prompt-gamma spectrum with conditions on fragment mass and with variable binsize added in folder "/dmp/EgammaA". Accumulation of prompt-neutron spectrum with variable bin size corrected.

NOTE : GEF Version 2015/2.1 should not be used any more.

— > Additional information on this version can be found here.

  • GEF-code, Version 2015/1.1, executables and source (January 2, 2015. Last modification September 23, 2015 : numerical problems with the new FreeBASIC compiler solved.) (Extended output options, covariances between results of different systems.)

— > Additional information on this version can be found here.

  • GEF-code, Version 2014/2.1, executables and source (March 25, 2014) (New global parameter set, new systematics of fission barriers)

— > Additional information on this version can be found here.

  • GEF-code, Version 2014/1.2, executables and source (January 25, 2014) (Modified description of multi-chance fission.)

— > Additional information on this version can be found here.

  • GEF-code, Version 2014/1.1, executables and source (January 4, 2014) (New global parameter set, modifications for better description of multi-chance fission.)

— > Additional information on this version can be found here.

  • GEF-code, Version 2013/2.2, executables and source (September 18 2013, updated December 6, 2013) (New global parameter set. Even-odd effect in fission-fragment neutron-number distribution revised. Mass distribution at high excitation energies revised. Angular momentum added as input parameter. Calculation of prompt-neutron emission improved. Output of pre-fission neutron and proton emission extended in tables and list-mode. List-mode output of energies and directions of post-scission neutrons. Multi-chance fission corrected and modified. Spurious even-odd effect in fission probabilites due to even-odd effect in theoretical shell correction removed.)

—> Additional information on this version can be found here.

Deterministic version of GEF

A determininistic version of the GEF code based on the folding method is provided to be coupled with an external nuclear-reaction code as a subroutine. Further information on this subroutine can be found here.

The authors will be happy about any comments or suggestions :
 Karl-Heinz Schmidt (e-mail : ) and Beatriz Jurado (e-mail :


Here are some examples of the code : (Black : experimental data, see report for references. Coulored : calculations with contributions of the individual fission channels) . Enlarge the figure.

GIF - 38.6 ko

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 [1] governs the interplay of macroscopic and microscopic effects. 

  • Three 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 [2].

  • The stiffness of the macroscopic potential with respect to mass asymmetry is deduced from the widths of measured mass distributions [3].

  • The excitation-energy-sorting mechanism [4, 5, 6] determines the prompt neutron yields and the odd-even effect in fission-fragment yields of even-Z and odd-Z systems [7].

  • Neutron evaporation is calculated with a Monte-Carlo statistical code using level densities from empirical systematics [8] and binding energies with theoretical shell effects [9] with gamma competition included.
  • References :

    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 and B. Jurado, Phys. Rev. Lett. 104 (2010) 212501, see also Maxwell’s demon on the nuclear level
    5. "Thermodynamics of nuclei in thermal contact"
      K.-H. Schmidt and B. Jurado, Phys. Rev. C 82 (2011) 014607
    6. "Final excitation energy of fission fragments"
      K.-H. Schmidt, B. Jurado, Phys. Rev. C 83 (2011) 061601(R)
    7. "Influence of complete energy sorting on the characteristics of the odd–even effect in fission-fragment element distributions"
      B. Jurado and K.-H. Schmidt, J. Phys. G : Nucl. Part. Phys. 42 (2015) 055101
    8. "Inconsistencies in the description of pairing effects in nuclear level densities"
      K.-H. Schmidt, B. Jurado, Phys. Rev. C 86 (2012) 044322"
    9. "Nuclear ground state masses and deformations"
      P. Moeller et al., Atom. Data Nucl. Data Tables 59 (1995) 185

    [1] Windows is a registered trademark of Microsoft Corp


    GEFY : GEF-based fission-fragment Yield library in ENDF-format

    Here you can download GEF-based fission-fragment yields in ENDF format. GEFY 6.1 (November 2016) : Independent and cumulative fission-fragment yields. Multi-chance fission is considered. Uncertainties reflect the uncertainties of the model. They are determined from calculations with perturbed model parameters. For this purpose, a series of calculations was performed with different sets of model parameters. Each parameter in these sets was varied randomly with a standard variation (...)

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    Download Final EFNUDAT Report for GEF

    General model description of fission observables by K.-H. SCHMIDT and B. JURADO CENBG, Chemin du Solarium B.P. 120, 33175 Gradignan, France Abstract : Structural effects in fission-product yields and neutron data for a large number of fissioning nuclei between 220Th and 262Rf from spontaneous fission to 14- MeV-neutron-induced fission have been used to deduce information on the properties of the fissioning systems. Macroscopic properties are attributed to the compound nucleus, while (...)

    Lire la suite