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

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/cm 3 ) Magnetic field (~ 330 nT - 1/1000 Earth) Magnetosphere Water presence at the poles (?) Planet formation theories

fluorescence spectra composition 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 Mercury formation Evaluation of the elemental composition of the crust of solar system objects planets asteroids moons Understanding the formation of the solar system as a whole solar system objects

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

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

Mission related problems Poor knowledge and no control on the measurement environment No repair possible in space Risk Analysis and 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 PHYSICALVALIDATION PHYSICAL VALIDATION GRID GRID transposition for statistically significant samples production NON-FUNCTIONAL REQUIREMENTS Results reliability, by means of PHYSICALVALIDATION PHYSICAL VALIDATION GRID GRID transposition for statistically significant samples production

● 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 The simulation Geant4 Low Energy Electromagnetic Package Geant4 Atomic Relaxation Package X-ray Fluorescence Emission model

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

PHASE I

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

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

PHASE II

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

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

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 Comparison between experimental and simulated entire distributions Complex materials Several peaks Physical background 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 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 Good agreement between simulations and experimental data (p >0.05) Geant4 Atomic Deexcitation Package Physics Validation Goodness-of-Fit Statistical Toolkit

Quantitative comparisons: Hawaiian basalt High statistical correlation between experimental data and simulations simulations experimental E BEAM =6.5 keV E BEAM =8.3 keV Fluorescence spectra from Hawaiian Basalt Energy (keV) Counts Fluorescence spectra from Hawaiian Basalt Pearson correlation analysis: r>0.93 p< A c (95%) = Anderson Darling test Beam Energy A

Simulation results: E BEAM =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) (E < 3.5 keV)

i Simulation results: E BEAM =7.0 keV Simulation results: E BEAM =8.3 keV

Simulation results: E BEAM =9.2 keV

Complex simulations require long execution time Execution time reducion gives fruibility for application DIANE allows GRID usage transaprently Integration for the application performed generally, available for any Geant4 application DIANE (Distributed Analysis Environment) 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

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 Rocks X-ray emission library libraryof simulated rocks spectra reference 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 HERMES EXPERIMENT risky Space missions are risky, so solid strategies for risk mitigation are to be undertaken

CONCLUSIONS Creation of rocks libraries of astrophysics interest Creation of rocks libraries of astrophysics interest simulated spectra are validated with respect to experimental data simulated spectra are validated with respect to experimental data generating rocks of known composition 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

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