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 3 fly-by (Mariner 10 - 1974-75) 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 (?)

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 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

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

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

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

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

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%

PHASE II

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

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

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

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>0.93 p<0.0001 Counts High statistical correlation between experimental data and simulations EBEAM=6.5 keV Energy (keV)

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 Simulation results: EBEAM=8.3 keV

Simulation results: EBEAM=9.2 keV

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

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 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: Alfonso.Mantero@ge.infn.it