NEA-1864 GEF 2025 V1.2.

GEF 2025 v1.2

GEF is publicly available under GNU GPLv3 license at https://git.oecd-nea.org/gef/code

DO NOT SUBMIT A REQUEST. DIRECTLY GO TO https://git.oecd-nea.org/gef/code

GEF is a semi-empirical framework designed to provide predictive descriptions of fission observables. It   relies on a set of underlying theoretical models that provide the structural basis of GEF. These models are generally valid for all nuclei, but they contain a number of adjustable parameters. The values of these parameters are chosen so that a wide range of experimental observables, including yields, total kinetic energies, prompt neutron spectra, and multiplicities, are reproduced with good accuracy. In this way, GEF is not a direct fit to experimental data, but instead a model framework refined through comparison with an extensive set of measurements.

GEF is a computer code for the simulation of the nuclear fission process. The GEF code calculates pre-neutron and post-neutron fission-fragment nuclide yields, angular-momentum distributions, isomeric yields, prompt-neutron yields and prompt-neutron spectra, prompt-gamma spectra, and several other quantities for a wide range of fissioning nuclei from mercury to seaborgium in spontaneous fission as well as in neutron- and proton-induced fission. Multi-chance fission (fission after emission of neutrons) is included. For neutron-induced fission, the pre-compound emission of neutrons is considered. Output is provided as tables and as parameters of fission observables on an event-by-event basis.

The full GEF version includes the calculation of beta-delayed processes, like emission of delayed neutrons and cumulative yields. In addition, it produces tables of fission yields (independent and cumulative yields) in ENDF-6 format.

Specific features of the GEF code:

• The mass division and the charge polarisation 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.

• 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 S1 and S2 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 [4,5,6,7,11] determines the prompt-neutron yields and the odd-even effect in fission-fragment yields of even-Z and odd-Z systems.

• Prompt neutron emission from the fragments is calculated with a Monte-Carlo statistical code using level densities from empirical systematics [8] and binding energies with theoretical shell effects with gamma competition included.

• Spectra and multiplicities of prompt gamma emission are provided. Non-statistical gamma emission is calculated with a dedicated VMI model.

• Model uncertainties, covariances and correlations are determined by a series of

• calculations with perturbed parameters. Covariances of fission yields from two different systems are available.

• Multi-chance fission is supported.

• Pre-compound emission of neutrons is considered for neutron-induced fission.

The Monte-Carlo method is used.

Uncertainties are deduced from perturbed calculations.

GEF can be applied to the fission of any particle-stable fissioning system, in particular between Z=76 and Z=120. Initial excitation energies range from zero (spontaneous fission) to 100 MeV. The upper limit is caused by the limitation in the applicability of the underlying theoretical models.

Running time is heavily case-dependent. A typical calculation with 100 000 events takes about 5 seconds on one processor of a recent Intel i7 CPU (2.80GHz). Calculations with perturbed parameters and calculations at higher excitation energies, where multi-chance fission occurs, require somewhat more time.

On the one hand, the results of GEF tend to agree better with available measured data than other, in particular microscopic, models, due to the presence of adjustable parameters. On the other hand, they deviate more from specific data that were measured with high accuracy than direct systematics, because a unique set of model parameters is used for all nuclei. GEF is aimed to make reliable predictions also for systems, where no empirical data are available

The main routines are written in FreeBASIC (http://www.freebasic.net/). FreeBASIC produces compiled binary code using the C run-time library. Graphics output is based on the X11 library. A graphical user interface is provided for Windows, written in JustBasic (http://www.justbasic.com/), which has a specific run-time library.

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. New insight into superfluid nuclear dynamics from the even-odd effect in fission, K.-H. Schmidt, B. Jurado, arXiv:1007.0741v1 [nucl-th]

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 nuclear level densities, K.-H. Schmidt, B. Jurado, Phys. Rev. C 86 (2012) 044322

9. General description of fission observables, K.-H. Schmidt, B. Jurado, Ch. Amouroux, JEFF-Report 24, NEA of OECD, 2014

10. Revealing hidden regularities with a general approach to fission K.-H. Schmidt, B. Jurado, Eur. Phys. J. A 51 (2015) 176

11. 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

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. Review on the progress in nuclear fission - experimental methods and theoretical descriptions K.-H. Schmidt, B. Jurado, Rep. Progr. Phys. 81 (2018) 106301

14. 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

15. 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) 13685

GEF can be compiled and installed in Windows and Linux, using exactly the same sources files. Specific executables are provided for the two systems. GEF was tested on Windows and Linux.

Memory < 250 Mbyte; Disc < 100 Mbyte, with higher requirements for outputs with more events generated.

Supports Windows and Linux.

Any Linux distribution, 32-bit or 64-bit. Some additional libraries need to be installed, see www.freebasic.net -> documentation -> using the FreeBASIC compiler -> Installing FreeBASIC. It is recommended to use the 32-bit version of FreeBASIC on a 64-bit system for better numerical stability. Please install the appropriate libraries.

Multi-chance fission is supported.

The results on neutron emission prior to fission and prompt-neutron emission between saddle and scission, and from the fragments are given separately. The sequence of the events in the list-mode output is sorted by energy at fission in the case of multi-chance fission in order to save computing time. An optional enhancement factor may be specified. A value >1 increases the statistics of the Monte-Carlo calculation and hence reduces the statistical uncertainties and fluctuations of the results. Default value is 100 000 events. This is adapted for a rough overview, but the number of events should be appreciably increased when accurate results are required. This is particularly useful to compare different systems, to study systematic trends and to determine reliable covariances.

GEF provides all results event by event in a list-mode file on demand.

K.-H. Schmidt

Erzhausen, Germany

Beatriz Jurado

CENBG

CNRS/IN2P3

Chemin du Solarium

B.P. 120

F-33175 Gradignan, France