GEF: A GEneral description of the Fission process.

CENBG, CNRS/IN2P3, Chemin du Solarium B.P. 120, 33175 Gradignan, France through the Nuclear Energy Agency Data Bank, Issy-les-Moulineaux, France.

BASIC (P00564PCX8603).

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 polonium to seaborgium in spontaneous fission and neutron-induced fission. The result refers to first-chance fission. Output is provided as tables and as values of fission observables on an event-by-event basis.

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 governs the interplay of macroscopic and microscopic effects.

· Four 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.

· 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 determines the prompt neutron yields and the odd-even effect in fission-fragment yields of even-Z and odd-Z systems.

· Neutron evaporation and gamma emission are calculated with a Monte-Carlo statistical code using level densities from empirical systematics and binding energies with theoretical shell effects. Gamma competition at energies above the neutron threshold is considered.

· Model uncertainties and covariances are determined by a series of calculations with perturbed parameters.

· Multi-chance fission is supported.

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

The official GEF websites are http://www.khs-erzhausen.de and http://www.cenbg.in2p3.fr/GEF .

The Monte-Carlo method is used. Uncertainties are deduced from perturbed calculations.

GEF can be compiled and installed under Windows and linux, using exactly the same sources files. Specific executables are provided for the two systems. The authors tested GEF on Windows and linux.

a) Windows XP or newer

b) Any Linux distribution. Eventually, some additional packages need to be installed, e.g. X11 developer tools.

The package includes precompiled executables for Windows operating systems. Linux users are required to download a free BASIC compiler: http://www.freebasic.net/. The main routines are written in FreeBASIC ( http://www.freebasic.net/ ). FeeBASIC 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 [a], written in JustBasic ( http://www.justbasic.com/ ), which has a specific run-time library. The Windows version of GEF runs also under WINE on LINUX.

**a)
Included Documentation:**

K.-H. Schmidt and B. Jurado, “General Model Description of Fission Observables” CENBG, CNRS/IN2P3, Chemin du Solarium B.P. 120, 33175 Gradignan, France (October, 2010).

Karl-Heinz Schmidt and Beatriz Jurado, “Prompt-Neutron and Prompt-Gamma Emission from a General Description of the Fission Process (JEF/DOC 1423).

**b)
Background Documentation:**

“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 Dynamics,” K.-H. Schmidt, B. Jurado, *Phys.
Rev. Lett. 104* (2010) 212501.

“New Insight into Superfluid
Nuclear Dynamics from the Even-Odd Effect in Fission,” K.-H. Schmidt, B.
Jurado, *arXiv:1007.0741v1* [nucl-th].

“Inconsistencies in the Description of Pairing Effects in Nuclear Level Densities,” K.-H. Schmidt, B. Jurado, Phys. Rev. C 86 (2012) 044322

The package is transmitted on one CD with the included references cited above, and a zip file containing the source code and precompiled executables for Windows and Linux systems.

March 2013, November 2013.

**KEYWORDS**: MONTE CARLO
METHOD, NUCLEAR FISSION, STATISTICAL MODELS