Models for the Simulation of X-Ray Fluorescence and PIXE

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Models for the Simulation of X-Ray Fluorescence
and PIXE

• A. Mantero, S. Saliceti, B. Mascialino, Maria
  Grazia Pia
• INFN Genova, Italy

NSS, Rome, 21 October 2004
http//www.ge.infn.it/geant4/lowE/index.html
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Fluorescence Emission
Original motivation from astrophysics requirements
Cosmic rays, jovian electrons
X-Ray Surveys of Asteroids and Moons
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
Wide field of applications beyond astrophysics
Courtesy ESA Space Environment Effects Analysis
Section
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X-ray fluorescence and Auger effect

• Calculation of shell cross sections
• Based on Livermore (EPDL) Library for
  photoelectric effect
• Based on Livermore (EEDL) Library for electron
  ionisation
• Based on Penelope model for Compton scattering
• Detailed atom description and calculation of the
  energy of generated photons/electrons
• Based on Livermore EADL Library
• Production threshold as in all other Geant4
  processes, no photon/electrons generated and
  local energy deposit if the transition predicts a
  particle below threshold

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Test process

• Unit, integration and system tests
• Verification of direct physics results against
  established references
• Comparison of simulation results to experimental
  data from test beams
• Pure materials
• Complex composite materials
• Quantitative comparison of simulation/experimental
  distributions with rigorous statistical methods
• Parametric and non-parametric analysis

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Verification X-ray fluorescence
Comparison of monocromatic photon lines generated
by Geant4 Atomic Relaxation w.r.t. reference
tables (NIST)
Transitions (Fe)
Transition Probability Energy
(eV) K L2 1.01391 -1 6349.85 K
L3 1.98621 -1 6362.71 K
M2 1.22111 -2 7015.36 K M3
2.40042 -2 7016.95 L2 M1
4.03768 -3 632.540 L2 M4
1.40199 -3 720.640 L3 M1
3.75953 -3 619.680 L3 M5
1.28521 -3 707.950
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Verification Auger effect
Auger electron lines from various materials
w.r.t. published experimental results
Precision 0.74 0.07
Cu Auger spectrum
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Test beam at Bessy
Advanced Concepts and Science Payloads
A. Owens, A. Peacock
Complex geological materials
Hawaiian basalt Icelandic basalt Anorthosite Doler
ite Gabbro Hematite
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Comparison with experimental data
Pearson correlation analysis rgt0.93
plt0.0001
Effects of detector response function presence
of trace elements
Experimental and simulated X-ray spectra are
statistically compatible at 95 C.L.
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PIXE

• Calculation of cross sections for shell
  ionization induced by protons or ions
• Two models available in Geant4
• Theoretical model by Grizsinsky intrinsically
  inadequate
• Data-driven model, based on evaluated data
  library by Paul Sacher (compilation of
  experimental data complemented by calculations
  from EPCSSR model by Brandt Lapicki)
• Generation of X-ray spectrum based on EADL
• Uses the common de-excitation package

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PIXE Cross section model

• Fit to Paul Sacher data library results of the
  fit are used to predict the value of a cross
  section at a given proton energy
• allow extrapolations to lower/higher E than data
  compilation
• First iteration, Geant4 6.2 (June 2004)
• The best fit is with three parametric functions
  for different groups of elements
• 6 Z 25
• 26 Z 65
• 66 Z 99

• Second iteration, Geant4 7.0 (December 2004)
• Refined grouping of elements and parametric
  functions, to improve the model at low energies

Next protons, L shell ions, K shell
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Quality of the PIXE model

• How good is the regression model adopted w.r.t.
  the data library?
• Goodness of model verified with analysis of
  residuals and of regression deviation
• Multiple regression index R2
• ANOVA
• Fishers test
• Results (from a set of elements covering the
  periodic table)
• 1st version (Geant4 6.2) average R2 99.8
• 2nd version (Geant4 7.0) average R2 improved to
  99.9 at low energies
• p-value from test on the F statistics lt 0.001 in
  all cases

Test statistics
Fisher distribution
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Bepi Colombo Mission to Mercury
Study of the elemental composition of Mercury by
means of X-ray fluorescence and PIXE Insight
into the formation of the Solar System
(discrimination among various models)
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A Library For Simulated X-Ray Emission form
Planetry Surfaces

• A. Mantero, S. Saliceti, B. Mascialino, Maria
  Grazia Pia
• INFN Genova, Italy
• A.Owens, ESA

NSS, Rome, 21 October 2004
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The BepiColombo Mission to Mercury
HERMES Is an X-Ray spectrometer to measure the
composition of the upper layers of planetary
surface

• Composed of 2 orbiters carrying a total of 25
  scientific experiments
• Magnetic Field Study
• Planet Surface Mapping
• Planet Surface Composition study
• 4 spectrometer (IR, X, ?, n)
• 1 laser altimeter

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X-Ray Detectors
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Rocks X-Ray Emission Library

• Space missions are risky, so solid strategies
  for risk mitigation are to be undertaken
• HERMES is an X-Ray spectrometer studying
  Mercury's surface composition
• Solid state detector have a better definition
  than normal gas-filled proportional counters
• We will measure detailed X-Ray spectra leading to
  detailed elemental composition of the crust of
  the planet

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Rocks X-Ray Emission Library
Test beams at BESSY labs have been undertaken in
order to provide a set of X-Ray spectra from PSSL
rocks that could be found rocky planets (Mars,
Venus, Mercury)
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Rocks Spectra Simulation
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Rocks Spectra Simulation
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Summary

• Geant4 provides precise models for detailed
  processes at the level of atomic substructure
  (shells)
• X-ray fluorescence, Auger electron emission and
  PIXE are accurately simulated
• Rigorous test process and quantitative
  statistical analysis for software and physics
  validation have been performed
• A new generation of X-Ray detectors will be used
  shortly for planetary investigations, giving
  precise results
• A library of rocks X-Ray spectra is needed for
  accurate physic reach and risk mitigation studies
• Geant4 is capable of generating X-Ray spectra for
  any rock of known composition and a library is
  under production.