Geant4 Physics Validation

Pablo Cirrone Giacomo Cuttone Francesco Di Rosa Susanna Guatelli Alfonso Mantero Barbara Mascialino Luciano Pandola Andreas Pfeiffer MG Pia Giorgio Russo Paolo Viarengo Valentina Zampichelli Geant4 Physics Validation M.G. Pia On behalf of the LowE EM and Advanced Examples Working Groups http://www.ge.infn.it/geant4/lowE Geant4 Space User Workshop Pasadena, 6-10 Novemver 2006

Geant4 Toolkit Wide set of physics processes and models Versatility of configuration according to use cases Provide objective criteria to evaluate Geant4 physics models • Document their precisionagainst experimental data • Test allGeant4 physics models systematically • Quantitative testswith rigorous statistical methods How to choose the most appropriate model for my simulation?

Verification and Validationof Geant4 physics • Verification • = compliance of the software results with the underlying model • Unit tests (at the level of individual Geant4 classes) • Validation • = comparison against experimental data • Quantitative estimate of the agreement between Geant4 simulation and reference data through statistical methods (Goodness-of-Fit) A systematic, quantitative validation of Geant4 physics models against reference experimental data is essential to establish the reliability of Geant4-based applications

IEEE Trans. Nucl. Sci., December 2006 25 July 2006. Statistical Toolkit • 2nd development cycle • Released April 2006 • What’s new • New tests • ROOT User Layer • New installation tools • Performance analysis The most complete software tool for 2-sample GoF tests

Geant4 Validation • Atomic relaxation • Bremsstrahlung • Proton Bragg peak • + other validation activities in Advanced Examples • Statistical Toolkit • Common features of the validation activities • Collaborative, open, transparent work environment • Rigorous, quantitative analysis • Publication-quality methods and results K. Amako et al., Comparison of Geant4 electromagnetic physics models against the NIST reference dataIEEE Trans. Nucl. Sci., Vol. 52, Issue 4, Aug. 2005, pp. 910-918

Geant4 Atomic Relaxation models Fluorescence Auger electron emission It is used by Geant4 packages: Low Energy Electromagnetic Photoelectric effect Low Energy electron ionisation Low Energy proton ionisation (PIXE) Penelope Compton scattering Hadronic Physics Nuclear de-excitation Radioactive decay Geant4 Atomic Relaxation • Geant4 Low Energy Electromagnetic package takes into account the detailed atomic structure of matter and the related physics processes • It includes a package for Atomic Relaxation • Simulation of atomic de-excitation resulting from the creation of a vacancy in an atom by a primary process These physics models are relevant to many diverse experimental applications

Geant4 fluorescence Original motivation from astrophysics requirements Cosmic rays, jovian electrons X-Ray Surveys ofAsteroids 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) 250 keV C, N, O line emissions included Wide field of applications beyond astrophysics Courtesy ESA Space Environment & Effects Analysis Section

Atomic Relaxation in Geant4 Two steps: • Identification of the atomic shell where a vacancy is created by a primary process(photoelectric, Compton, ionisation) • The creation of the vacancy is based on the calculation of the primary process cross sections relative to the shells of the target atom • Cross section modeling and calculation specific to each process • Generation of the de-excitation chain and its products • Common package, used by all vacancy-creating processes • Geant4 Atomic Relaxation • Generation of fluorescence photons and Auger electrons • Determination of the energy of the secondary particles produced

Modelling foundationin Geant4 Low Energy Electromagnetic Package • Calculation of shell cross sections • Based on the EPDL97 Livermore Library for photoelectric effect • Based on the EEDLLivermore 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 the EADL Livermore Library

Validation of Geant4 Atomic Relaxation • Previous partial validation studies (collaboration with ESA) • Pure materials: limited number of materials examined • Complex materials: complex experimental set-up, large uncertainties on the target material composition • Systematic validation project: NIST database as reference Authoritative, systematic collection of experimental data

Method and tools • Geant4 test code to generate fluorescence and Auger transitions from all elements • Geant4 Atomic Relaxation handles 6 ≤ Z ≤ 100 • Selection of experimental data subsets from NIST database • The NIST database also contains data from theoretical calculations • Comparison of simulated/NIST data with Goodness-of-Fit test • Data grouped for the comparison as a function of Z according to the initial vacancy and transition type • Statistical Toolkit (http://www.ge.infn.it/statisticaltoolkit) • Kolmogorov-Smirnov test • The result of the agreement is expressed through the p-value of the test

Fluorescence - Shell-start 1 E (keV)  Geant4 ○ NIST Z

Fluorescence - Shell-start 3  Geant4 ○ NIST

Auger electron emission • Scarce experimental data in the NIST database • Often multiple data for the same Auger transition: ambiguous reference • Analysis in progress: comparison of Geant4 simulation data against the NIST subset of experimental data • Preliminary results: good qualitative agreement as in the case of X-ray fluorescence • Rigorous statistical analysis to be completed, will be included in publication

Geant4 electron Bremsstrahlung 2 electromagnetic physics packages Standard Low Energy 3 Bremsstrahlung processes G4eLowEnergyBremsstrahlung G4eBremsstrahlung Tsai Tsai 2BN 2BS angular distribution angular distributions G4PenelopeBremsstrahlung

Validation of Geant4 EM physics Ongoing large-scale project NIST Photon mass attenuation coefficient Range, Stopping power (e, p, a) K. Amako et al., IEEE Trans. Nucl. Sci. 52 (2005) 910 Atomic relaxation (fluorescence, Auger effect) Proton Bragg peak Electron Bremsstrahlung NSS 2006 Bremsstrahlung Difficult to find reference data Thin/thick target experiments Difficult to disentangle effects (because of the continuous part) 1st validation cycle: focus on low energy

θ The experimental set-up e- beam(70 keV-10 MeV) incident on a slab of material Photon (energy, θ) Electrons andd-rays are absorbed Bremsstrahlung photons can be transmitted electrons Z axis Yield,EnergyandPolar Angleof the emittedphotons Secondary production threshold = 0.5 mm Statistical Toolkit Goodness-of-Fit test in progress Quantitatitative comparison of experimental - simulated distributions

Preliminary results Work in progress! Data sets N. Starfelt et al., Phys. Rev. 102 (1956) 1598 Thin target: Be, Al, Au - 2.7, 4.5, 9.7 MeV Double differential cross sections W.E. Dance et al., Journal of Appl. Phys. 39 (1968) 2881 Thick target: Al, Fe – 0.5, 1 MeV Double differential cross sections Integrated g yield R. Ambrose et al., NIM B 56/57 (1991) 327 Absolute and relative yield

data data + + simulation simulation Double differentialsat 2.7 MeV on thin (2.63 mg/cm2) Be target N. Starfelt et al., Phys. Rev. 102 (1956) 1598 Energy (MeV) Energy (MeV)

data data + + simulation simulation Double differential s at 4.5 MeV on thin (2.63 mg/cm2) Be target N. Starfelt et al., Phys. Rev. 102 (1956) 1598 Energy (MeV) Energy (MeV)

data data + + simulation simulation Double differential s at 9.7 MeV on thin (2.63 mg/cm2) Be target N. Starfelt et al., Phys. Rev. 102 (1956) 1598 Energy (MeV) Energy (MeV)

data data + + simulation simulation Double differential s at 2.7 MeV on thin (0.878 mg/cm2) Al target N. Starfelt et al., Phys. Rev. 102 (1956) 1598 Energy (MeV) Energy (MeV)

data data + + simulation simulation Double differential s at 2.7 MeV on thin (0.209 mg/cm2) Au target N. Starfelt et al., Phys. Rev. 102 (1956) 1598 Energy (MeV) Energy (MeV)

data data + + simulation simulation Double differential s at 4.5 MeV on thin (0.209 mg/cm2) Au target N. Starfelt et al., Phys. Rev. 102 (1956) 1598 Energy (MeV) Energy (MeV)

data data + + simulation simulation Double differential sat 9.7 MeV on thin (0.209 mg/cm2) Au target N. Starfelt et al., Phys. Rev. 102 (1956) 1598 Energy (MeV) Energy (MeV)

500 keV Angular distribution W.E. Dance et al., Journal of Applied Physics 39 (1968) 2881 Ethr = 46 keV 500 keV electrons on Al (0.548 g/cm2)and Fe (0.257 g/cm2) Thick target experiment Standard package Red = data Black = simulation o  Al   Fe Absolute comparison

500 keV Angular distribution W.E. Dance et al., Journal of Applied Physics 39 (1968) 2881 precise agreement!

500 keV Angular distribution W.E. Dance et al., Journal of Applied Physics 39 (1968) 2881

1 MeV Angular distribution Same test for 1 MeV primary electrons (threshold: 50 keV) Standard package W.E. Dance et al., Journal of Applied Physics 39 (1968) 2881 Targets: Al (0.548 g/cm2) and Fe (0.613 g/cm2) Red = data Black = simulation o  Al   Fe Absolute comparison

1 MeV Angular distribution W.E. Dance et al., Journal of Applied Physics 39 (1968) 2881 precise agreement! Good agreement for Al - Reasonable also for Fe (2BN)

1 MeV Angular distribution W.E. Dance et al., Journal of Applied Physics 39 (1968) 2881 2BS: good for Al and Fe (except in the backward direction)

Integral g yield Total g yield on Al integrated on  (0  p) and on energy (Eth  Emax) Also available for other flavours of Geant4 Bremsstrahlung models W.E. Dance et al., Journal of Applied Physics 39 (1968) 2881 o  dat a   simul. Preliminary Further investigation in progress

70 keV Angular distributions Low Energy Package Penelope Standard Low Energy (TSAI) Penelope TSAI 2BS 2BN Angle (deg) Angle (deg) Angular distribution of photons is strongly model-dependent

Energy distribution at 70 keV Penelope Low Energy - TSAI R. Ambrose et al., Nucl. Instr. Meth. B 56/57 (1991) 327 Intensity/Z (eV/sr keV) photon direction 70 keV e- 45 deg Photon energy (keV) 70 keV electrons impinging on Al (25.4 mg/cm2)

Relative comparison at 70 keV Low Energy - TSAI Penelope Intensity/Z (eV/sr keV) Intensity/Z (eV/sr keV) Photon energy (keV) Photon energy (keV) Relative comparison (45° direction) Shapes of the spectra are in good agreement

K. Amako et al., Comparison of Geant4 electromagnetic physics models against the NIST reference dataIEEE Trans. Nucl. Sci., Vol. 52, Issue 4, Aug. 2005, pp. 910-918 • Adopt the same method also for hadronic physics validation • address all modeling options • start from the bottom (low energy) • progress towards higher energy based on previous sound assessments • statistical analysis of compatibility with experimental data • Guidance to users based on objective ground • not only “educated-guess” PhysicsLists Statistical Toolkit Goodness-of-Fit test Quantitatitative comparison of experimental - simulated distributions

Medical Physics High Energy Physics Space Science Astronauts’ radiation protection LHC Radiation Monitors Oncological radiotherapy Proton Bragg peak • Compare various Geant4 electromagnetic models • Assess lowest energy range of hadronic interactions • elastic scattering • pre-equilibrium + nuclear deexcitation • to build further validation tests on solid ground • Results directly relevant to various experimental use cases

Standard Low Energy – ICRU 49 Low Energy – Ziegler 1977 Low Energy – Ziegler 1985 Low Energy – Ziegler 2000 New “very low energy” models Parameterized (à la GHEISHA) Nuclear Deexcitation Default evaporation GEM evaporation Fermi break-up Pre-equilibrium Precompound model Bertini model Elastic scattering Parameterized models Bertini Intra-nuclear cascade Bertini cascade Binary cascade Relevant Geant4 physics models Hadronic Electromagnetic Subset of results shown here Full set of results in publication coming shortly

Resolution 100 m 2 mm Markus Chamber Sensitive Volume = 0.05 cm3 Experimental data CATANA hadrontherapy facility in Catania, Italy • high precision experimental data satisfying rigorous medical physics protocols • Geant4 Collaboration members Validation measurements Markus Ionization chamber

Geant4 simulation Accurate reproduction of the experimental set-up This is the most difficult part to achieve a quantitative Geant4 physics validation Geometry and beam characteristics must be known in detail and with high precision Ad hoc beam line set-up for Geant4 validation to enhance peculiar effects of physics processes Eproton = 63.5 MeV sE = 300 keV

Electromagnetic processes Electromagnetic options • Standard EM • Low Energy EM – ICRU 49 • Low Energy EM – Ziegler 1977 • Low Energy EM – Ziegler 1985 • Low Energy EM – Ziegler 2000

Standard EM Electromagnetic processes • Standard EM: p, ions, g, e- e+ 1 M events Geant4 Experimental data CvM Cramer-von Mises test KS Kolmogorov-Smirnov test AD Anderson-Darling test mm

LowE EM – ICRU49 Electromagnetic processes • Low Energy EM – ICRU49: p, ions • Low Energy EM – Livermore: g, e- • Standard EM : e+ 1 M events Geant4 Experimental data CvM Cramer-von Mises test KS Kolmogorov-Smirnov test AD Anderson-Darling test mm

LowE EM – Ziegler 1977 Electromagnetic processes • Low Energy EM – Ziegler 1977: p, ions • Low Energy EM – Livermore: g, e- • Standard EM : e+ 1 M events Geant4 Experimental data CvM Cramer-von Mises test KS Kolmogorov-Smirnov test AD Anderson-Darling test mm

LowE EM – Ziegler 1985 Electromagnetic processes • Low Energy EM – Ziegler 1985: p, ions • Low Energy EM – Livermore: g, e- • Standard EM : e+ 1 M events Subject to further investigation Geant4 Experimental data mm

Geant4 Physics Validation