Test Beam Simulation for ESA BepiColombo Mission

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

2. Mercury • Atmosphere generated by solar wind • High density (5.3 g/cm3) • Magnetic field (~ 330 nT - 1/1000 Earth) • Magnetosphere • Water presence at the poles (?) • Observations from Earth are difficult • Impossible observations from Hubble • - optics damage Planetary crust composition Planet Interplanetary Spacecrafts 3 fly-by (Mariner 10 - 1974-75) Formation Solar System

3. 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

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

5. 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 • PHYSICALVALIDATION • GRIDtransposition for statistically significant samples production Mission related problems • Poor knowledge and no control on the measurement environment • No repair possible in space Risk Analysis and Mitigation

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

7. Comparison with experimental data Photon energy 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%

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

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

10. Modeling the experimental set-up Rock samples irradiation and fluorescence emission measurement Geant4 Deexcitation Physics Validation Creation of a reference database The simulation reproduces: - Complex geological materials - Experimental Geometry - Response and efficiency of the detector

11. The physics involved is based on the Low Energy Electromagnetic Package - Atomic Deexcitation - Fluorescence Emission Future test beam Test beams contributed significantly to the validation of Geant4 Low Energy Electromagnetic Package/Atomic Deexcitation Physics involved PIXE

12. Simulation results: test beam validation Fluorescence spectra from Iceland Basalt E=8.3 keV Agreement between simulations and experimental data Counts Fluorescence spectra from Iceland Basalt simulations experimental Energy (keV) High statistical correlation between experimental data and simulations (p< 0.001) Counts E=6.5 keV Energy (keV)

13. Pure elements Complex materials 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 Parametrical analysis of the results Several peaks Physical background Good agreement between simulations and experimental data (p >0.05) Comparison between experimental and simulated entire distributions Statistical Analysis Atomic Deexcitation Physical Validation

14. i Simulation Results • Differences between simulations and experimental data are ascribable to: • - The nominal composition is different from the real one • (extra peaks are due to K and L lines of Cr) • The detector response is not well known at low energies • (E < 3.5 keV) • - Contaminations within the test beam (?)

15. 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

16. CONCLUSIONS (I) ESA BepiColombo Physics Complex materials modelisation Modelisation of the entire experimental set-up Validation of the Deexcitation Package

17. CONCLUSIONS (II) This is one of the advanced examples of the unique using the Low Energy Package with fluorescence emission Creation of rocks libraries of astrophysics interest simulated spectra are validated with respect to experimental data Future developments: - other rocks simulations (irradiated with solar spectra) - simulation code optimisation, - simulation of the BepiColombo Mission as a whole Paper submission to IEEE- Transactions on Nuclear Science: Novembre 2004

18. Alfonso.Mantero@ge.infn.it