Maria Grazia Pia, INFN Genova Precision Electromagnetic Physics in Geant4: the Atomic Relaxation...
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Transcript of Maria Grazia Pia, INFN Genova Precision Electromagnetic Physics in Geant4: the Atomic Relaxation...
Maria Grazia Pia, INFN Genova
Precision Electromagnetic Physics in Geant4: Precision Electromagnetic Physics in Geant4:
thethe Atomic Relaxation Models Atomic Relaxation Models
A. Mantero, B. Mascialino, Maria Grazia Pia, S. Saliceti
INFN Genova, Italy
http://www.ge.infn.it/geant4/lowE/index.html
CHEP, Interlaken, 27-30 September 2004
Maria Grazia Pia, INFN Genova
Geant4 Low Energy Electromagnetic PhysicsGeant4 Low Energy Electromagnetic PhysicsGeant4 provides a specialised package to handle electromagnetic interactions down to low energy
“Low” means up to 100 GeV
Electrons and Electrons and photonsphotons
Electrons and Electrons and photonsphotons
Positive charged Positive charged hadrons and ionshadrons and ionsPositive charged Positive charged hadrons and ionshadrons and ions
Negative charged Negative charged hadronshadrons
Negative charged Negative charged hadronshadrons
Models based on Livermore Library (EEDL, EPDL)
Penelope re-engineering
down to 250 eV (lower in principle)
down to 100 eV
Bethe-Bloch
Ziegler/ICRU Parameterisations
Free electron gas
Quantum Harmonic Oscillator
+ same as positive hadrons
~ MeV region
low energy (down to ~ionisation potential)
high energy
low energy (< 1 keV)
Maria Grazia Pia, INFN Genova
VisionPrecise process modeling
– Cross sections, angular distributions
Charge dependence– Relevant at low energies
Take into account the atomic structure of matter– Detailed description of atoms (shells)
Secondary effects after the primary process– De-excitation of the atom after the creation of a vacancyDe-excitation of the atom after the creation of a vacancy
X-ray fluorescence
Auger electron emission
PIXE (Particle Induced X-ray Emission)
Photon transmission, 1m Pb
shell effects
Atomic RelaxationAtomic Relaxation
following the creation of a vacancy by photoelectric effect, Compton effect and ionisation
Maria Grazia Pia, INFN Genova
The process in a nutshellRigorous software process
– Iterative and incremental model– Based on the Unified Process: bidimensional, static + dynamic dimension– Use case driven, architecture centric– Continuous software improvement process
User Requirements Document – Updated with regular contacts with users
Analysis and design– Design validated against use cases
Unit, package integration, system tests + physics validation– We do a lot… but we would like to do more– Limited by availability of resourcesavailability of resources for core testing– Rigorous quantitative tests, applying statistical methods
Peer design and code reviews– We would like to do more… main problem: geographical spread + overwork
Close collaboration with users
Maria Grazia Pia, 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
Use case: fluorescence emission
Original motivation from astrophysics requirements
Wide field of applications beyond astrophysics
Maria Grazia Pia, INFN Genova
DesignUsed by processes
Maria Grazia Pia, INFN Genova
Implementation
Two steps:
Identification of the atomic shell where a vacancy is created by a primary process (photoelectric, Compton, ionisation), based on the calculation of cross sectionscross sections at the shell level
– Cross section modeling and calculation specific to each process
Generation of the de-excitation chain and its productsproducts– Common package, used by all vacancy-creating processes– Also used by Geant4 hadronic package, at the end of the nuclear de-excitation chain
(e.g. radioactive decay)
Maria Grazia Pia, INFN Genova
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
Maria Grazia Pia, INFN Genova
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
Test PlanTest Guidelines Test Automation ArchitectureTest CasesTest DataTest Results
Maria Grazia Pia, INFN Genova
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)
Maria Grazia Pia, INFN Genova
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
Maria Grazia Pia, INFN Genova
Test beam at Bessy - 1
Monocromatic photon beamHpGe detector
• Cu• Fe• Al
• Si• Ti• Stainless steel
Pure material samples:
Advanced Concepts and Science PayloadsA. Owens, A. Peacock
Maria Grazia Pia, INFN Genova
Comparison with experimental data
Parametric analysis:fit to a gaussian
Compare experimental and simulated distributions
Detector effects!(resolution, efficiency)
Photon energy
Experimental dataSimulation
Precision better than 1%
% difference of photon energies
Maria Grazia Pia, INFN Genova
Test beam at Bessy - 2Advanced 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
Maria Grazia Pia, INFN Genova
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 testBeam Energy
4.96.58.29.5
A20.040.010.210.41
Fluorescence spectrum of Icelandic Basalt8.3 keV beam
Counts
Energy (keV)
Effects of detector response function + presence of trace elements
Pearson correlation analysis:r>0.93 p<0.0001
Maria Grazia Pia, INFN Genova
PIXE
Calculation of cross sections for shell ionisation 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
Maria Grazia Pia, INFN Genova
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
Maria Grazia Pia, INFN Genova
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
Maria Grazia Pia, INFN Genova
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)
Maria Grazia Pia, INFN Genova
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
Beware: intrinsic precision of physics modeling and comparison intrinsic precision of physics modeling and comparison with test beam results are two different aspectswith test beam results are two different aspects
– both must be verified
Thanks to ESA for the support and collaboration to development and physics validation
Don’t worry… it is not just for space science(also used at LHC!)(also used at LHC!)