1. 6 October 2005 Geant4 Workshop, Leuven, Belgium Geant4 Model of SIXS Particle Instrument and Preliminary Simulation Results Lehti, J. (ASRO) Valtonen, E. (ASRO) Vainio, R. (University of Helsinki) jussi.lehti@asro-space.com

2. 6 October 2005Geant4 Workshop, Leuven, Belgium Outline SIXS particle instrument SIXS particle instrument Geant4 model of SIXS Geant4 model of SIXS Simulations results Simulations results Future plans Future plans

3. 6 October 2005Geant4 Workshop, Leuven, Belgium SIXS Experiment SIXS Experiment Solar Intensity X-ray and particle Spectrometer onboard MPO Scientific objectives: Provide the primary solar radiation spectrum for X-ray fluorescence measurements Study coronal X-ray and energetic particle emission BepiColombo - SIXS BepiColombo mission BepiColombo mission ESA cornerstone mission to Mercury ESA cornerstone mission to Mercury Launch 2012 Launch 2012 Five years’ cruise phase, one year operation at orbit Five years’ cruise phase, one year operation at orbit Double S/C mission: Double S/C mission: Mercury Planetary Orbiter (MPO) Mercury Planetary Orbiter (MPO) three-axis stabilized three-axis stabilized z-axis nadir pointing z-axis nadir pointing 400 x 1500 km orbit 400 x 1500 km orbit Mercury Magnetospheric Orbiter (MMO) Mercury Magnetospheric Orbiter (MMO)

4. 6 October 2005Geant4 Workshop, Leuven, Belgium SIXS Particle Instrument SIXS Particle Instrument SIXS Particle Instrument 2π sr Field-of-View around anti-nadir with Geometric Factor of ~ 0.1 cm2 sr Five GaAs surface detectors around a HgI2 core detector Measures 0.1 - 3 MeV electrons 1 - 30 MeV protons ΔE/E ~ 50 % energy channel separation coarse directional resolution 64-s/1-s time resolution

5. 6 October 2005Geant4 Workshop, Leuven, Belgium Geant4 model (1/2) Geometry Geometry Core detector Core detector 4x4x4 mm3 4x4x4 mm3 Mercuric iodide (HgI 2 ) Mercuric iodide (HgI 2 ) Side detectors Side detectors Thickness 50 μm Thickness 50 μm Gallium Arsenide (GaAs) Gallium Arsenide (GaAs) Supporting structure Supporting structure Aluminum Aluminum G4Box solids (16 pcs) G4Box solids (16 pcs) Foils above side detectors Foils above side detectors Thickness 25 μm Thickness 25 μm Beryllium Beryllium Screen capture from VRML browser

6. 6 October 2005Geant4 Workshop, Leuven, Belgium Geant4 model (2/2) Physics Physics LE EM package LE EM package Output Output Ascii file Ascii file CSV CSV Human readable Human readable Easy to read with different analysis software Easy to read with different analysis software Energy losses and incident direction Energy losses and incident direction

7. 6 October 2005Geant4 Workshop, Leuven, Belgium Simulations Electron and proton separation Particle identification is based on ΔE/E method Particle identification is based on ΔE/E method Special case

8. 6 October 2005Geant4 Workshop, Leuven, Belgium Simulations Electron and proton separation Special case: Special case: Particles do not trigger the core detector Particles do not trigger the core detector  Separation is not possible Solution: Solution: Reduce from the detected Reduce from the detected intensity the intensity of the protons which stopped in the side detector Energy Intensity ~1.4 MeV

9. 6 October 2005Geant4 Workshop, Leuven, Belgium Simulations Electron and proton separation electrons protons

10. 6 October 2005Geant4 Workshop, Leuven, Belgium Simulations Energy resolution Isotropic and beam particle sources Isotropic and beam particle sources Beam represents a “perfect” collimation Beam represents a “perfect” collimation Detected energy channels are normalized to unity Detected energy channels are normalized to unity X-, Y-, Z-axes are logarithmic X-, Y-, Z-axes are logarithmic Ideal instrument  line Ideal instrument  line

11. 6 October 2005Geant4 Workshop, Leuven, Belgium Future plans Geometric factor and response function simulations Geometric factor and response function simulations Use the model to improve performance of the instrument Use the model to improve performance of the instrument More detailed geometry implementation More detailed geometry implementation More realistic particle sources, e.g. real intensity spectra, anisotropies More realistic particle sources, e.g. real intensity spectra, anisotropies