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)

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 (?) Interplanetary Spacecrafts 3 fly-by (Mariner 10 - 1974-75) 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 Named in honour of Giuseppe Colombo - Planetary evolutionary models

Launch

- Solar corona measurements

date 2012

- Precision measurements of general relativity - Search for Near Earth Objects (NEO) MPO Mercury Magnetospheric Orbiter Mercury Planetary Orbiter

HERMES experiment

Planetary surface composition measurements by means of X-ray spectrography Fluorescence spectra E BEAM =8.5 keV Incident Radiation Fluorescence Mercury soil 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 • 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

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 Pure element irradiation PHASE II Geological complex samples irradiation

PHASE I

Test beam at Bessy - I

Advanced Concepts and Science Payloads

A. Owens, T. Peacock

Pure material samples:

• Cu • Fe • Al • Si • Ti • Stainless steel

Monocromatic photon beam

HPGe detector detector 67 mm 45° beam 40 mm 40 mm material samples

Simulation validation - I

Photon energy: mean Experimental data Simulation % difference of photon energies Parametric analysis: fit to a gaussian 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 Advanced Concepts and Science Payloads

A. Owens, T. Peacock

Monocromatic photon beam

Hawaiian basalt Icelandic basalt Anorthosite Dolerite Gabbro Hematite

FCM beamline GaAs Si Si reference XRF chamber

Modeling the experimental set-up

The simulation reproduces: Complex

geological materials Geometry

of the experimental set-up

Response efficiency

and 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 Good agreement between simulations and experimental data (p >0.05)

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 Complex materials Several peaks Physical background Comparison between experimental and simulated entire distributions

Geant4 Atomic Deexcitation Package Physics Validation

Anderson Darling test

Beam Energy

4.9

6.5

8.2

9.5

A 2

0.04

0.01

0.21

0.41

A c (95%) = 0.752

Fluorescence spectra from Hawaiian Basalt

simulations experimental

Fluorescence spectra from Hawaiian Basalt

Quantitative comparisons: Hawaiian basalt

Energy (keV) E BEAM =6.5 keV Energy (keV) Pearson correlation analysis: r>0.93 p<0.0001

High statistical correlation between experimental data and simulations

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)

Simulation results: E

BEAM

=7.0 keV

• i

Simulation results: E

BEAM

=8.3 keV

Simulation results: E

BEAM

=9.2 keV

DIANE (Distributed Analysis Environment)

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

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]