Models for the Simulation of X-Ray Fluorescence and PIXE A. Mantero, S. Saliceti, B. Mascialino, Maria Grazia Pia INFN Genova, Italy NSS, Rome, 21 October 2004 http://www.ge.infn.it/geant4/lowE/index.html

Fluorescence Emission Cosmic rays, jovian electrons Original motivation from astrophysics requirements X-Ray Surveys of Asteroids and Moons Solar X-rays, e, p Geant3.21 ITS3.0, EGS4 Courtesy SOHO EIT Geant4 Induced X-ray line emission: indicator of target composition (~100 mm surface layer) C, N, O line emissions included Wide field of applications beyond astrophysics Courtesy ESA Space Environment & Effects Analysis Section

X-ray fluorescence and Auger effect Calculation of shell cross sections Based on Livermore (EPDL) Library for photoelectric effect Based on Livermore (EEDL) Library for electron ionisation Based on Penelope model for Compton scattering Detailed atom description and calculation of the energy of generated photons/electrons Based on Livermore EADL Library Production threshold as in all other Geant4 processes, no photon/electrons generated and local energy deposit if the transition predicts a particle below threshold

Test process Unit, integration and system tests Verification of direct physics results against established references Comparison of simulation results to experimental data from test beams Pure materials Complex composite materials Quantitative comparison of simulation/experimental distributions with rigorous statistical methods Parametric and non-parametric analysis

Verification: X-ray fluorescence Comparison of monocromatic photon lines generated by Geant4 Atomic Relaxation w.r.t. reference tables (NIST) K transition K transition Transitions (Fe) Transition Probability Energy (eV) K L2 1.01391 -1 6349.85 K L3 1.98621 -1 6362.71 K M2 1.22111 -2 7015.36 K M3 2.40042 -2 7016.95 L2 M1 4.03768 -3 632.540 L2 M4 1.40199 -3 720.640 L3 M1 3.75953 -3 619.680 L3 M5 1.28521 -3 707.950

Verification: Auger effect 366.25 eV (367) 428.75, 429.75 eV (430 unresolved) 436.75, 437.75 eV (437 unresolved) Auger electron lines from various materials w.r.t. published experimental results Precision: 0.74 % ± 0.07 Cu Auger spectrum

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

Comparison with experimental data Pearson correlation analysis: r>0.93 p<0.0001 Effects of detector response function + presence of trace elements 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 Experimental and simulated X-ray spectra are statistically compatible at 95% C.L.

PIXE Calculation of cross sections for shell ionization induced by protons or ions Two models available in Geant4: Theoretical model by Grizsinsky – intrinsically inadequate Data-driven model, based on evaluated data library by Paul & Sacher (compilation of experimental data complemented by calculations from EPCSSR model by Brandt & Lapicki) Generation of X-ray spectrum based on EADL Uses the common de-excitation package

PIXE – Cross section model Fit to Paul & Sacher data library; results of the fit are used to predict the value of a cross section at a given proton energy allow extrapolations to lower/higher E than data compilation First iteration, Geant4 6.2 (June 2004) The best fit is with three parametric functions for different groups of elements 6 ≤ Z ≤ 25 26 ≤ Z ≤ 65 66 ≤ Z ≤ 99 Second iteration, Geant4 7.0 (December 2004) Refined grouping of elements and parametric functions, to improve the model at low energies Next: protons, L shell ions, K shell

Quality of the PIXE model How good is the regression model adopted w.r.t. the data library? Goodness of model verified with analysis of residuals and of regression deviation Multiple regression index R2 ANOVA Fisher’s test Results (from a set of elements covering the periodic table) 1st version (Geant4 6.2): average R2 99.8 2nd version (Geant4 7.0): average R2 improved to 99.9 at low energies p-value from test on the F statistics < 0.001 in all cases Residual deviation Total deviation Regression deviation Test statistics Fisher distribution

Bepi Colombo Mission to Mercury Study of the elemental composition of Mercury by means of X-ray fluorescence and PIXE Insight into the formation of the Solar System (discrimination among various models)

A Library For Simulated X-Ray Emission form Planetry Surfaces A. Mantero, S. Saliceti, B. Mascialino, Maria Grazia Pia INFN Genova, Italy A.Owens, ESA NSS, Rome, 21 October 2004

The BepiColombo Mission to Mercury HERMES Is an X-Ray spectrometer to measure the composition of the upper layers of planetary surface Composed of 2 orbiters carrying a total of 25 scientific experiments: Magnetic Field Study Planet Surface Mapping Planet Surface Composition study 4 spectrometer (IR, X, , n) 1 laser altimeter

Basalt fluorescence spectrum X-Ray Detectors Solid State Detectors Better Resolution - 140 eV @ 5.89 KeV” Greater Efficiency at low Energies Faster count speed Basalt fluorescence spectrum Beam Energy 9.5 KeV Counts Energy (KeV) Gas Detectors Poor resolution - “< 1KeV @ 5.95 KeV” Poor efficiency at low energies Only for some elements Ka lines can be detected (Mg, Al, Si, S, Ca, Ti, and Fe)

Rocks X-Ray Emission Library Space missions are risky, so solid strategies for risk mitigation are to be undertaken HERMES is an X-Ray spectrometer studying Mercury's surface composition Solid state detector have a better definition than “normal” gas-filled proportional counters We will measure detailed X-Ray spectra leading to detailed elemental composition of the crust of the planet We need to study 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 Test beams at BESSY labs have been undertaken in order to provide a set of X-Ray spectra from PSSL rocks that could be found rocky planets (Mars, Venus, Mercury) Si GaAs FCM beamline Si reference XRF chamber A total of 8 rocks have been irradiated and by now 5 of them have been simulated. Basalt (Hawaii, Madagascar and Iceland) Anorthosite Ematite Gabbro Dolerite (Whin Sill, Java) Obsidian

Rocks Spectra Simulation Geant4 provides advanced instruments for the description of geometry and materials Thanks to a Geant4 simulation we can simulate any rock of known composition with a high degree of confidence

Rocks Spectra Simulation

Summary Geant4 provides precise models for detailed processes at the level of atomic substructure (shells) X-ray fluorescence, Auger electron emission and PIXE are accurately simulated Rigorous test process and quantitative statistical analysis for software and physics validation have been performed A new generation of X-Ray detectors will be used shortly for planetary investigations, giving precise results A library of rocks X-Ray spectra is needed for accurate physic reach and risk mitigation studies Geant4 is capable of generating X-Ray spectra for any rock of known composition and a library is under production.