Transcript Measurements of the Radiation Belts from MIR and STRV 1994

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. Urban
with acknowledgements to
J. Stepanek (PSI, Villigen, CH)
R. Cullen (LLNL, U.S.)
See CERN/INFN pre-print at http://www.estec.esa.nl/wmwww/wma/news.html
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Applications for
LowEnergy 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
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Energy cut-offs
 Geant3.21
 EGS4, ITS3.0
 Geant4 “standard models”
- Photoelectric effect
- Compton effect
- Bremsstrahlung
- Ionisation (d-rays)
- Multiple scattering
 Geant4 low-energy models
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10 keV
1 keV
10 keV
10 keV
1 keV
1 keV
1 keV
250 eV
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X-Ray Surveys of Asteroids and
Moons
Cosmic rays,
jovian electrons
Solar X-rays, e, p
Geant3.21
ITS3.0, EGS4
Courtesy SOHO EIT
Induced X-ray line emission:
indicator of target composition
(~100 mm surface layer)
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C, N, O line emissions included
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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
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…to be implemented:
Processes included:
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Compton scattering
Photoelectric effect
Rayleigh effect
Pair production
Bremsstrahlung
Ionisation
Fluorescence
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 Auger effect
 Positrons
New physics
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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.
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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)
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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:
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P(T,t,Bi) =
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S
j=2
aj(T)
______
(t + Bi) j
, T<T0
c(T)/t2
, T>T0
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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.
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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
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