ESA Space Environment & Effects Analysis Section

1. ESA Space Environment & Effects Analysis Section Low-Energy Extension of Electromagnetic Processes J. Apostolakis, A. Forti, S. Giani, M. Maire, P. Nieminen, M.G. Pia, P.R. Truscott, L. Urbanwith acknowledgements toJ. Stepanek (PSI, Villigen, CH)R. Cullen (LLNL, U.S.)See CERN/INFN pre-print at http://www.estec.esa.nl/wmwww/wma/news.html SREW Workshop

2. ESA Space Environment & Effects Analysis Section Applications for Low-Energy E-M Extension • Mineralogical surveys of asteroids and moons by induced X-ray line emission • Analysis of background effects in X- and g-ray astrophysical observatories • Neutrino experiments; fundamental physics • Medical applications: Hadron treatment (secondary particles) • DNA and cellular studies SREW Workshop

3. ESA Space Environment & Effects Analysis Section Energy cut-offs • Geant3.21 10 keV • EGS4, ITS3.0 1 keV • Geant4 “standard models” - Photoelectric effect 10 keV - Compton effect 10 keV - Bremsstrahlung 1 keV - Ionisation (d-rays) 1 keV - Multiple scattering 1 keV • Geant4 low-energy models250 eV SREW Workshop

4. ESA Space Environment & Effects Analysis Section X-Ray Surveys of Asteroids and Moons Cosmic rays, jovian electrons Solar X-rays, e, p Geant3.21 ITS3.0, EGS4 Courtesy SOHO EIT Geant4 Induced X-ray line emission: indicator of target composition (~100 mm surface layer) C, N, O line emissions included SREW Workshop

5. ESA Space Environment & Effects Analysis Section Features • Validity range from 250 eV to 100 GeV • Elements Z=1 to 100 • Two phases: 1) Calculation of total cross section, 2) Generation of the final state. • Data bases: - EADL (Evaluated Atomic Data Library), - EEDL (Evaluated Electrons Data Library), - EPDL97 (Evaluated Photons Data Library) from LLNL. • A version of libraries especially formatted for use with Geant4 available from Geant4 distribution source SREW Workshop

6. ESA Space Environment & Effects Analysis Section …to be implemented: Processes included: • Compton scattering • Photoelectric effect • Rayleigh effect • Pair production • Bremsstrahlung • Ionisation • Fluorescence • Auger effect • Positrons New physics SREW Workshop

7. ESA Space Environment & Effects Analysis Section Compton scattering • Energy distribution of the scattered photon according to Klein-Nishina formula multiplied by scattering functions F(q) from EPDL97 data library. Angular distribution also based on EPDL97. Rayleigh effect • Angular distribution: F(E,q)=[1+cos2(q)]F2(q), where F(q) is the form factor obtained from EPDL97. Photoelectric effect • Subshell from which the electron is emitted selected according to the cross sections of the sub-shells. De-excitation via isotropic fluorescence photons; transition probabilities from EADL. SREW Workshop

8. ESA Space Environment & Effects Analysis Section Bremsstrahlung • Probability of emission of a photon with kinetic energy t, considering an electron of incident energy T: P(T,t) = a(T)/t + b(T) • Values of a and b: Fitting from energy distributions of the emitted photon available in the EEDL. • Direction of the outgoing electron the same as that of the incoming one; angular distribution of the emitted photons generated according to a simplified formula based on the Tsai cross section (expected to become isotropic in the low-E limit) SREW Workshop

9. ESA Space Environment & Effects Analysis Section Ionisation • Total cross section at a given energy calculated by summing the partial cross sections for all of the subshells of an element, obtained from an interpolation of the cross section data in the EEDL. • Sub-shell from which the electron is emitted selected according to the values of the subshell cross sections. • Probability of d-ray emission with kinetic energy t from a sub-shell of binding energy Bi, with incoming electron of kinetic energy T: 7 aj(T) S ______ , T<T0 (t + Bi) j P(T,t,Bi) = j=2 , T>T0 c(T)/t2 SREW Workshop

10. ESA Space Environment & Effects Analysis Section Ionisation (contd.) • ~20% of the subshells (transition elements), modified fitting • Angle of emission of the scattered electron and of the d-ray determined by energy-momentum conservation. • Interaction leaves the atom in an excited state, with excitation energy equal to the binding energy of the sub-shell from which the d-ray has been emitted. De-excitation via fluorescence photons. SREW Workshop

11. ESA Space Environment & Effects Analysis Section SREW Workshop

12. ESA Space Environment & Effects Analysis Section SREW Workshop

13. ESA Space Environment & Effects Analysis Section SREW Workshop

14. ESA Space Environment & Effects Analysis Section Conclusions • A set of models has been developed to extend the Geant4 coverage of electro-magnetic interactions of photons and electrons down to 250 eV. • Wide user community foreseen in astrophysics, space applications, medical field, ... • Further extensions and refinements planned by the Geant4 Collaboration in the future •  Data base accuracy  feedback from user community… • Low-E protons: http://www.estec.esa.nl/wmwww/wma/news.html SREW Workshop