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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
Mercury
• Observations from Earth are difficult
• Impossible observations from Hubble
(optics damage)
Interplanetary Spacecrafts
Atmosphere generated by solar wind
3 fly-by (Mariner 10 - 1974-75)
High density (5.3 g/cm3)
Magnetic field (~ 330 nT - 1/1000 Earth)
Magnetosphere
Water presence at the poles (?)
Planet formation theories
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
The ESA BepiColombo mission
Two orbiters for a variety of scientific experiments:
Magnetic field study - Planet mapping - Surface study
- Planetary evolutionary models
Launch
- Solar corona measurements
date 2012
- Precision measurements of general relativity
- Search for Near Earth Objects (NEO)
MPO
Mercury
Mercury
Magnetospheric
Orbiter
Named in
honour of
Giuseppe
Colombo
Planetary
Orbiter
HERMES experiment
Planetary surface composition measurements by means of X-ray spectrography
Fluorescence spectra
EBEAM=8.5 keV
Incident Radiation
Mercury soil
Counts
Fluorescence
Solar radiation variability
+
Cosmic Radiation
Energy (keV)
Detector for incident radiation
monitoring
Choice for the most appropriate detector
under study, particularly for GaAs.
Mission related problems
• Poor knowledge and no control on
the measurement environment
Risk Analysis
and
• No repair possible in space
Mitigation
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
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
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
PHASE I
Test beam at Bessy - I
Advanced Concepts and Science Payloads
A. Owens, T. Peacock
Pure material samples:
• Cu
• Si
• Fe
• Al
• Ti
• Stainless steel
Monocromatic photon beam
HPGe detector
detector
67 mm
40 mm
45°
beam
40 mm
material samples
Simulation validation - I
Photon energy: mean
Experimental data
Simulation
Parametric analysis:
fit to a gaussian
% difference of photon energies
Compare experimental
and simulated
distributions
Detector effects
- resolution
- efficiency
Precision better than 1%
PHASE II
Test beam at Bessy - II
Complex geological
materials of
astrophysical interest
Hawaiian basalt
Icelandic basalt
Anorthosite
Dolerite
Gabbro
Hematite
Advanced Concepts and Science Payloads
FCM beamline
A. Owens, T. Peacock
Monocromatic photon beam
Si
Si reference
GaAs
XRF
chamber
Modeling the experimental set-up
The simulation reproduces:
Complex geological
materials
Geometry of the
experimental set-up
Response and
efficiency of the
detector
Simulation design
Detector (Si(Li)) response function and efficiency reproduction
User-friendly modification of experimental set-up
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
Statistical analysis
Goodness-of-Fit
Statistical Toolkit
Anderson-Darling
test
• Goodness-of-Fit test
belonging to Kolmogorov test
family
Good agreement
between simulations
and experimental data
(p >0.05)
• Not sensitive to data
binning
• No need for symmetric
distributions
Complex
materials
Several peaks
Physical background
Comparison between
experimental and simulated
entire distributions
• No threshold counts/bin
Geant4 Atomic Deexcitation Package
Physics Validation
Fluorescence spectra from Hawaiian Basalt
Anderson Darling test
0.04
0.01
0.21
0.41
Counts
Beam Energy
4.9
6.5
8.2
9.5
Quantitative
comparisons:
Hawaiian basalt
EBEAM=8.3 keV
A2
Ac (95%) = 0.752
Fluorescence spectra from Hawaiian Basalt
simulations
experimental
Energy (keV)
Counts
Pearson correlation
analysis:
r>0.93
EBEAM=6.5 keV
Energy (keV)
p<0.0001
High statistical correlation
between experimental data and
simulations
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)
Simulation results: EBEAM=7.0 keV
• i
Simulation results: EBEAM=8.3 keV
Simulation results: EBEAM=9.2 keV
DIANE
(Distributed Analysis Environment)
Complex simulations require
long execution time
DIANE allows GRID
usage transaprently
Execution time reducion gives
fruibility for application
Integration for the application
performed generally, available
for any Geant4 application
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
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
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
Future developments
Mercury incident radiation is composed by
Solar radiation
Cosmic radiation
A new model for
VALIDATION
Future test beam
is available in Geant4
For further informations:
[email protected]