1. Test Beam Simulation for ESA BepiColombo Mission
Monte Carlo 2005
Chattanooga, April 2005
Marcos Bavdaz, Alfonso Mantero, Barbara Mascialino, Petteri Nieminen, Alan Owens, Tone Peacock, Maria Grazia Pia

3. Mercury Observations from Earth are difficult
Impossible observations from Hubble (optics damage)
Interplanetary Spacecrafts
3 fly-by (Mariner )
Atmosphere generated by solar wind
High density (5.3 g/cm3)
Magnetic field (~ 330 nT - 1/1000 Earth)
Magnetosphere
Planet formation theories
Water presence at the poles (?)

4. Mercury formation
Evaluation of the elemental composition of the crust of
solar system objects
planets
asteroids
moons
solar system objects
Understanding the formation of
the solar system as a whole
A number of missions are planned in the coming years to measure the fluorescence spectra of solar system object, as a method to ascertain their composition

5. The ESA BepiColombo mission
Two orbiters for a variety of scientific experiments:
Magnetic field study - Planet mapping - Surface study
Named in honour of Giuseppe Colombo
- Planetary evolutionary models
- Solar corona measurements
- Precision measurements of general relativity
- Search for Near Earth Objects (NEO)
Launch
date 2012
MPO
Mercury
Planetary
Orbiter
Mercury
Magnetospheric
Orbiter

6. HERMES experiment Mercury soil Solar radiation variability +
Planetary surface composition measurements by means of X-ray spectrography
Fluorescence spectra
EBEAM=8.5 keV
Incident Radiation
Fluorescence
Mercury soil
Counts
Solar radiation variability +
Cosmic Radiation
Energy (keV)
Choice for the most appropriate detector under study, particularly for GaAs.
Detector for incident radiation monitoring

7. Mission related problems
Poor knowledge and no control on the measurement environment
No repair possible in space
Risk Analysis
and
Mitigation
Simulation
FUNCTIONAL REQUIREMENTS
Fluorescence simulation resulting from atomic deexcitation
Reproduction capability for complex materials, like the geological ones
Geometry detailed description
Detector features reproduction
NON-FUNCTIONAL REQUIREMENTS
Results reliability, by means of
PHYSICAL VALIDATION
GRID transposition for statistically significant samples production

8. The simulation
It is a based application for the simulation of X-ray emission spectra from rock geological samples of astrophysical interest
The physics involved is based on the
Geant4 Low Energy Electromagnetic Package
Geant4 Atomic Relaxation Package
X-ray Fluorescence Emission model

9. The simulation validation
The simulation has been validated with comparison to experimental data taken at Bessy by ESA in two different phases:
PHASE I
PHASE II
Pure element
irradiation
Geological complex samples irradiation

10. PHASE I

11. Pure material samples:
Test beam at Bessy - I
Advanced Concepts and Science Payloads
A. Owens, T. Peacock Cu Fe Al Si Ti
Stainless steel
Pure material samples:
Monocromatic photon beam
HPGe detector

12. Simulation validation - I
Photon energy: mean
Experimental data
Simulation
Parametric analysis:
fit to a gaussian
Compare experimental and simulated distributions
Detector effects
- resolution
- efficiency
% difference of photon energies
Precision better than 1%

13. PHASE II

14. Test beam at Bessy - II
Complex geological materials of astrophysical interest
Advanced Concepts and Science Payloads
A. Owens, T. Peacock
Monocromatic photon beam Si
GaAs
FCM beamline
Si reference
XRF chamber
Hawaiian basalt
Icelandic basalt
Anorthosite
Dolerite
Gabbro
Hematite

15. Modeling the experimental set-up
The simulation reproduces:
Complex geological materials
Geometry of the experimental set-up
Response and efficiency of the detector

16. Simulation design
Detector (Si(Li)) response function and efficiency reproduction
User-friendly modification of experimental set-up

17. Simulation validation - II
The application demonstrates Geant4 capability to generate the fluorescence spectra resulting from complex materials
Quantitative analysis: comparison on the entire distribution
non-parametric testing techniques

18. Anderson-Darling test
Statistical analysis
Anderson-Darling test
Goodness-of-Fit test belonging to Kolmogorov test family
Not sensitive to data binning
No need for symmetric distributions
No threshold counts/bin
Comparison between experimental and simulated entire distributions
Complex materials
Several peaks
Physical background
Goodness-of-Fit Statistical Toolkit
Good agreement between simulations and experimental data (p >0.05)
Geant4 Atomic Deexcitation Package Physics Validation

19. High statistical correlation between experimental data and simulations
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
Fluorescence spectra from Hawaiian Basalt
EBEAM=8.3 keV
Quantitative comparisons:
Hawaiian basalt
Counts
Fluorescence spectra from Hawaiian Basalt
Energy (keV)
simulations
experimental
Pearson correlation analysis:
r> p<0.0001
Counts
High statistical correlation between experimental data and simulations
EBEAM=6.5 keV
Energy (keV)

20. Simulation results: EBEAM=6.5 keV
Differences between simulations and experimental data are ascribable to:
- The nominal composition of the rock could be different from the real one
(extra peaks are due to K and L lines of Cr)
The detector response is “unknown” at low energies
(E < 3.5 keV)

21. Simulation results: EBEAM=7.0 keV Simulation results: EBEAM=8.3 keV

22. Simulation results: EBEAM=9.2 keV

23. DIANE (Distributed Analysis Environment)
Execution time reducion gives fruibility for application
Complex simulations require long execution time
Integration for the application performed generally, available for any Geant4 application
DIANE allows GRID usage transaprently
2 tests: public cluster (30 – 35 machines LXPLUS) and dedicated cluster (15 machines LXSHARE)
Execution times reduction:
~ one order of magnitude (24h – 750M events)
IN COLLABORATION WITH JUKUB MOSCICKI

24. Rocks X-ray emission library
Space missions are risky, so solid strategies for risk mitigation are to be undertaken
HERMES EXPERIMENT
It is necessary to study all the possible responses of the instruments before they are in flight with a very good precision for all the possible situations they can find
The simulation development has open the possibility to create a library of simulated rocks spectra, to be used as a reference for various planetary missions
SMART-1
BepiColombo
Venus Express

25. CONCLUSIONS Creation of rocks libraries of astrophysics interest
simulated spectra are validated with respect to experimental data
Geant4 is capable of generating X-Ray spectra for rocks of known composition
The production of an extensive library is in progress
Test beams contributed significantly to the validation of Geant4 Low Energy Electromagnetic Package/Atomic Deexcitation

26. Future developments PIXE For further informations:
Solar radiation
Mercury incident radiation is composed by
Cosmic radiation
A new model for
VALIDATION
PIXE
Future test beam
is available in Geant4
For further informations: