1. 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

2. Fluorescence Emission
Cosmic rays,
jovian electrons
Original motivation from astrophysics requirements
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

3. 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

4. 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

5. Verification: X-ray fluorescence
Comparison of monocromatic photon lines generated by Geant4 Atomic Relaxation w.r.t. reference tables (NIST)
K transition
K transition
Transitions (Fe)
Transition Probability Energy (eV)
K L
K L
K M
K M
L2 M
L2 M
L3 M
L3 M

6. Verification: Auger effect
eV (367)
428.75, eV (430 unresolved)
436.75, eV (437 unresolved)
Auger electron lines from various materials w.r.t. published experimental results
Precision: 0.74 % ± 0.07
Cu Auger spectrum

7. Advanced Concepts and Science Payloads
Test beam at Bessy
Advanced Concepts and Science Payloads
A. Owens, A. Peacock
Complex geological materials Si
GaAs
FCM beamline
Si reference
XRF chamber
Hawaiian basalt
Icelandic basalt
Anorthosite
Dolerite
Gabbro
Hematite

8. Comparison with experimental data
Pearson correlation analysis:
r> p<0.0001
Effects of detector response function + presence of trace elements
Ac (95%) = 0.752
Anderson Darling test
Beam Energy
4.9
6.5
8.2
9.5 A2
0.04
0.01
0.21
0.41
Experimental and simulated X-ray spectra are statistically compatible at 95% C.L.

9. 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

10. 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

11. 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
Fisher’s 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 < in all cases
Residual deviation
Total deviation
Regression deviation
Test statistics
Fisher distribution

12. 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)

13. 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

14. 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

15. Basalt fluorescence spectrum
X-Ray Detectors
Solid State Detectors
Better Resolution
KeV”
Greater Efficiency at low Energies
Faster count speed
Basalt fluorescence spectrum
Beam Energy 9.5 KeV
Counts
Energy (KeV)
Gas Detectors
Poor resolution
- “< 5.95 KeV”
Poor efficiency at low energies
Only for some elements Ka lines can be detected (Mg, Al, Si, S, Ca, Ti, and Fe)

16. 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
We need to study possible responses of the instruments before they are in flight with a very good precision for all the possible situations they can find

17. 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) Si
GaAs
FCM beamline
Si reference
XRF chamber
A total of 8 rocks have been irradiated and by now 5 of them have been simulated.
Basalt (Hawaii, Madagascar and Iceland)
Anorthosite
Ematite
Gabbro
Dolerite (Whin Sill, Java)
Obsidian

18. Rocks Spectra Simulation
Geant4 provides advanced instruments for the description of geometry and materials
Thanks to a Geant4 simulation we can simulate any rock of known composition with a high degree of confidence

19. Rocks Spectra Simulation

20. 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.