Low Energy Livermore Model

Additional electromagnetic physics processes for photons, electrons, hadrons and ions have been implemented in Geant4 in order to extend the validity range of particle interactions to lower energies than those available in the standard Geant4 EM [eal99]. Since the atomic shell structure is more important in most cases at low energies than it is at higher energies, the low energy processes make direct use of shell cross section data. The standard processes, which are optimized for high energy physics applications, often rely on parameterizations of these data.

Low energy processes include the photo-electric effect, Compton scattering, Rayleigh scattering, gamma conversion, bremsstrahlung and ionisation. Also atomic de-excitation module is implemented within this sub-package, which includes fluorescence and Auger electron emission of excited atoms. The implementation of low energy processes is valid for elements with atomic number between 1 and 99, and for energies down to 10 eV, upper limit depends on the process.

The data used for the determination of cross-sections and for sampling of the final state are extracted from a set of publicly distributed evaluated data libraries:

  • EPDL97 (Evaluated Photons Data Library) [CHK89];

  • EPICS2014 (Evaluated Photons Data Library) [NEA];

  • EEDL (Evaluated Electrons Data Library) [STPerkins89];

  • EADL (Evaluated Atomic Data Library) [PCeal];

  • binding energy values based on data of Scofield [Sco75].

Evaluated data sets are produced through the process of critical comparison, selection, renormalization and averaging of the available experimental data, normally complemented by model calculations. These libraries provide the following data:

  • total cross-sections for photoelectric effect, Compton scattering, Rayleigh scattering, pair production and bremsstrahlung;

  • subshell integrated cross sections for photo-electric effect and ionisation;

  • energy spectra of the secondaries for electron processes;

  • scattering functions for the Compton effect;

  • binding energies for electrons for all subshells;

  • transition probabilities between subshells for fluorescence and the Auger effect.

These data are used directly or are transformed into Geant4 format specific for each model. The author of EPDL97, who is also responsible for the EPICS2014, EEDL, and EADL data libraries, Dr. Red Cullen, has kindly permitted the libraries and their related documentation to be distributed with the Geant4 toolkit. The data are reformatted for Geant4 input and are inside the G4LEDATA data set, which may be downloaded from the Geant4 download page.

The EADL, EPICS2014, EEDL and EPDL97 data-sets are also available from several public distribution centres in a format different from the one used by Geant4 [NEAb].

Bibliography

CHK89

D. Cullen, J.H. Hubbell, and L. Kissel. Epdl97: the evaluated photon data library, ‘97 version. UCRL–50400, 6(Rev.5):, 1989. http://reddog1.llnl.gov/homepage.red/photon.htm.

eal99

J. Apostolakis et al. Geant4 low energy electromagnetic models for electrons and photons. Technical Report, CERN, CERN/INFN, 1999. CERN-OPEN-99-034(1999), INFN/AE-99/18.

NEA

NEA:. Electron photon interaction cross section library. https://www.oecd-nea.org/tools/abstract/detail/iaea1435/. [Online; accessed 26-october-2017].

NEAb

NEA:. Evaluated nuclear reaction data. http://www.oecd-nea.org/dbdata/data/evaluated.htm. [Online; accessed 26-october-2017].

PCeal

S.T. Perkins, D.E. Cullen, and M.H. Chen et al. Tables and graphs of atomic subshell and relaxation data derived from the llnl evaluated atomic data library (eadl), z=1-100. Technical Report UCRL-50400 Vol.30.

STPerkins89

S.M.Seltzer S.T.Perkins, D.E.Cullen. Tables and graphs of electron-interaction cross-sections from 10 ev to 100 gev derived from the llnl evaluated electron data library (eedl), z=1-100. Technical Report UCRL-50400 Vol.31, Lawrence Livermore National Laboratory, 1989.

Sco75

J.H. Scofield. Radiative Transitions in Atomic Inner-Shell Processes B.Crasemann ed. Academic Press, New York, 1975.