alfonso mantero, infn genova models for the simulation of x-ray fluorescence and pixe a. mantero, s....

Alfonso Mantero, INFN Genova

Models for the Simulation of X-Ray Models for the Simulation of X-Ray Fluorescence and PIXEFluorescence and PIXE

A. Mantero, S. Saliceti, B. Mascialino, Maria Grazia Pia

INFN Genova, Italy

http://www.ge.infn.it/geant4/lowE/index.html

NSS, Rome, 21 October 2004

Alfonso Mantero, INFN Genova Courtesy ESA Space Environment & Effects Analysis Section

X-Ray Surveys of Asteroids and Moons

Induced X-ray line emission:indicator of target composition(~100 m surface layer)

Cosmic rays,jovian electrons

Geant3.21

ITS3.0, EGS4

Geant4

Solar X-rays, e, p

Courtesy SOHO EIT

C, N, O line emissions included

Fluorescence Emission Original motivation from astrophysics requirements

Wide field of applications beyond astrophysics


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

Transition Probability Energy (eV)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

K transition

K transition

Transitions (Transitions (FeFe))

Comparison of monocromatic photon lines generated by Geant4 Atomic Relaxation w.r.t. reference tables (NIST)


Verification: Auger effect

Auger electron lines from various materials w.r.t.

published experimental results366.25 eV (367)

428.75, 429.75 eV (430 unresolved)

436.75, 437.75 eV (437 unresolved)

Precision: 0.74 % ± 0.07

Cu Auger

spectrum


Test beam at BessyAdvanced Concepts and Science Payloads

A. Owens, A. Peacock

SiSi

GaAsGaAs

FCM beamlineFCM beamline

Si referenceSi reference

XRF chamberXRF chamber

Complex geological materials

Hawaiian basaltIcelandic basalt

AnorthositeDoleriteGabbro

Hematite


Comparison with experimental data

Experimental and simulated X-ray spectra are statistically compatiblestatistically compatible at 95% C.L. 95% C.L.

Ac (95%) = 0.752

Anderson Darling test

Beam Energy4.96.58.29.5

A20.040.010.210.41

Effects of detector response function + presence of trace elements

Pearson correlation analysis:r>0.93 p<0.0001


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 modelFit 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 modelHow 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 Bepi Colombo Mission to MercuryMission 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 A Library For Simulated X-Ray Emission form Planetry SurfacesEmission 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

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

HERMESIs an X-Ray spectrometer to measure the composition of the upper layers of planetary

surface


X-Ray Detectors

Gas Detectors

• Poor resolution

- “< 1KeV @ 5.95 KeV”

• Poor efficiency at low energies

Only for some elements K lines can be detected (Mg, Al, Si, S, Ca, Ti, and

Fe)

Solid State Detectors

• Better Resolution

- 140 eV @ 5.89 KeV”• Greater Efficiency at low Energies• Faster count speed

Basalt fluorescence spectrumBeam Energy 9.5 KeV

Cou

nts

Energy (KeV)


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

● 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 We need to study possible responses of the instruments before they are in flight with a very good instruments before they are in flight with a very good precision for all the possible situations they can findprecision for all the possible situations they can find


Rocks X-Ray Emission LibraryTest 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) SiSi

GaAsGaAs

FCM beamlineFCM beamline

Si Si referencereferenceXRF XRF chamberchamberA 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


SummaryGeant4 provides precise models for detailed processes at the level of atomic substructure (shells)

X-ray fluorescenceX-ray fluorescence, Auger electronAuger electron emission and PIXEPIXE are accurately simulated

Rigorous test process and quantitative statistical analysisquantitative 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-Raylibrary of rocks X-Ray spectraspectra is needed for accurate physic reach and risk mitigation studies

Geant4 is capable of generatinggenerating X-Ray spectra for any rock of any rock of known compositionknown composition and a library is under production.

alfonso mantero, infn genova models for the simulation of x-ray fluorescence and pixe a. mantero, s....

Documents