1. LICENCE AND COPYRIGHT

The development of the GEF code has been supported by the European Union,
EURATOM 6, Framework Program "European Facilities for Nuclear Data
Measurements" (EFNUDAT), contract number FP6-036434, the Framework
Program "European Research Infrastructure for Nuclear Data Applications"
(ERINDA), and by the Nuclear Energy Agency of the OECD.

The GEF code is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.

Copyright 2009, 2010, 2011, 2012, 2013: 
Dr. Karl-Heinz Schmidt, Rheinstraße 4, 64390 Erzhausen, Germany
and 
Dr. Beatriz Jurado, Centre d'Etudes Nucleaires de Bordeaux-Gradignan,
Chemin du Solarium, Le Haut Vigneau, BP 120, 33175 Gradignan, Cedex,
France 

2. NAME OF THE PROGRAM:  GEF 2013/1.7

3. DESCRIPTION OF PROGRAM OR FUNCTION

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. 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.

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 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] determines the prompt 
neutron yields and the odd-even effect in fission-fragment yields of even-Z 
and odd-Z systems.
- Neutron evaporation 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.
- 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.lp2ib.in2p3.fr/GEF.

4. METHOD OF SOLUTION

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

5. TYPICAL RUNNING TIME

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

6. RELATED AND AUXILIARY PROGRAMS

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.
                                     
7. 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, 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

8. HARDWARE REQUIREMENTS

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

Memory < 50 MByte; Disc < 100 MByte, eventually more for event-wise output.

9. PROGRAMMING LANGUAGE(S) USED

Computer language
on Linux: FreeBASIC; on Windows [a]: FreeBASIC and JustBasic

10. OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED

a) Windows [a] XP or newer
b) Any Linux distribution. Eventually, some additional packages need to be 
installed, e.g. X11 developer tools.

11. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTION

Multi-chance fission is supported, except when a distribution of excitation
energies at fission is provided on input. The results on neutron emission
prior to fission and prompt-neutron emission 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 of the results. Default value
is 1.E5 events. With this value, the statistical uncertainties
are already smaller than the model uncertainties in most cases.
Higher statistics may be 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.

12. NAME AND ESTABLISHMENT OF AUTHORS

K.-H. Schmidt, Rheinstr. 4, 64390 Erzhausen, Germany B. Jurado, CENBG,
CNRS/IN2 P3, Chemin du Solarium B.P. 120, F-33175 Gradignan, France