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Precision validation of Geant4 electromagnetic physics Katsuya Amako, Susanna Guatelli, Vladimir Ivanchenko, Michel Maire, Barbara Mascialino, Koichi Murakami, Petteri Nieminen, Luciano Pandola, Sandra Parlati, Andreas Pfeiffer, Maria Grazia Pia, Michela Piergentili, Takashi Sasaki, Lazslo Urban Monte Carlo 2005 Topical Meeting Chattanooga, April 2005 Introduction is an object-oriented toolkit for the simulation of the passage of particles through matter It offers an ample set of complementary and alternative physics models for both electromagnetic and hadronic interactions, based on: theory experimental data parameterisations The validation of Geant4 physics models with respect to authoritative reference data is a critical issue, fundamental to establish the reliability of Geant4-based simulations. Aim of the project • Validation of Geant4 electromagnetic models against established references (ICRU - NIST), with the purpose of to evaluate their accuracy and to document their respective strengths • Simulation of physics quantities in the same experimental set-up as reference data • Rigorous quantitative statistical comparison PHYSICAL TEST Scope Quantitative statistical analysis GOODNESS-OF-FIT TESTING - Evaluation of Geant4 physics models goodness - How the various Geant4 models behave in the same experimental condition - Systematic data analysis allows to improve the physics models and guarantees the reliability Geant4 Electromagnetic Physics models Geant4 includes a number of packages to handle the e.m. interactions of electrons and positrons, gamma, X-ray and optical photons, muons, charged hadrons, ions • • • • • • • • • • • • • • • • • • multiple scattering bremsstrahlung ionisation annihilation photoelectric effect Compton scattering Rayleigh effect gamma conversion e+e- pair production synchrotron radiation transition radiation Cherenkov refraction reflection absorption scintillation fluorescence Auger Standard Package Geant4 Electromagnetic Package LowEnergy Package Muon Package specialised according to Optical - the particle type managed, - the energy range of processes covered. photon Package Alternative and complementary models are provided in the various packages for the same physics process High energy models – fundamental for LHC experiments, cosmic ray experiments etc. Low energy models – fundamental for space and medical applications, neutrino experiments, antimatter spectroscopy etc. – two “flavours” of models: • model based on Livermore libraries • à la Penelope Physics quantities under study • Photon Mass Attenuation Coefficient • Photon Partial Interaction Coefficient (mass attenuation coefficients with only one process activated) • Electron CSDA range and Stopping Power (no multiple scattering, no energy fluctuations) • Proton CSDA range and Stopping Power (no multiple scattering, no energy fluctuations) • Alpha CSDA range and Stopping Power (no multiple scattering, no energy fluctuations) Elements: Be, Al, Si, Fe, Ge, Ag, Cs, Au, Pb, U + water Ionisation potentials of the selected materials were modified w.r.t. the default values in Geant4, and were set as in the NIST database. Energy range: 1 keV – 100 GeV photon 10 keV – 1 GeV electron 1 keV – 10 GeV proton 1 keV – 1 GeV alpha Testing activity has been automatised (INFN Gran Sasso Laboratory and KEK) Simulation results - The simulation results were produced with Geant4 version 6.2. - The Geant4 test process verifies that the accuracy of the physics models will not deteriorate in future versions of the toolkit with respect to the results presented here. - Results obtained can be considered as an objective guidance to select the Geant4 electromagnetic models most appropriate to any specific simulation application. Statistical analysis • The statistical analysis has been performed by means of a Goodness-of-Fit Statistical Toolkit, specialised in the comparison of data distributions • The two alternative hypothesis under test are the following: H0: Geant4 simulations = NIST data H1: Geant4 simulations ≠ NIST data GoF Toolkit GoF test (χ2 test) Distance between Geant4 simulations and NIST reference data p < 0.05: Geant4 simulations and NIST data differ significantly p > 0.05: Geant4 simulations and NIST data do not differ significantly Test result (p-value) The p-value represents the probability that the test statistics has a value at least as extreme as that observed, assuming the null hypothesis is true 0≤p≤1 Test of Geant4 photon processes Photon mass attenuation coefficient Physics models under test: 1 keV – 100 GeV • Geant4 Standard Experimental • Geant4 Low Energy – EPDL set-up • Geant4 Low Energy – Penelope Reference data: Transmitted 1 I Monochromatic ln • NIST - XCOM photons (I) d I 0 photon beam (I ) o p-value stability study Mass attenuation coefficient in Fe Geant4 LowE Penelope Geant4 Standard Geant4 LowE EPDL NIST - XCOM • The three Geant4 models reproduce total attenuation coefficients with high accuracy • The two Geant4 LowE models exhibit the best agreement with reference data H0 REJECTION AREA Compton interaction coefficient 1 keV – 100 GeV Physics models under test: • Geant4 Standard • The three Geant4 models reproduce • Geant4 Low Energy – EPDL Compton scattering cross sections with high • Geant4 Low Energy – Penelope accuracy Reference data: • The Geant4 LowE – EPDL model exhibits the • NIST - XCOM best overall agreement with reference data Compton interaction coefficient in Ag c Geant4 LowE Penelope Geant4 Standard Geant4 LowE EPDL NIST - XCOM p-value stability study A ( )c NAV H0 REJECTION AREA Photoelectric interaction coefficient 1 keV – 100 GeV Physics models under test: • Geant4 Standard • The three Geant4 models • Geant4 Low Energy – EPDL reproduce photoelectric cross sections with high accuracy • Geant4 Low Energy – Penelope Reference data: • The two Geant4 LowE models • NIST - XCOM exhibit the best agreement Photoelectric interaction coefficient in Ge Geant4 LowE Penelope Geant4 Standard A phEPDL ( ) ph Geant4 LowE NAV NIST - XCOM Geant4 LowE Penelope Geant4 Standard Geant4 LowE EPDL NIST - XCOM p-value stability study H0 REJECTION AREA Pair production interaction coefficient 1 keV – 100 GeV Physics models under test: • Geant4 Standard • The three Geant4 models reproduce pair • Geant4 Low Energy – EPDL production cross sections with high accuracy • Geant4 Low Energy – Penelope Reference data: • NIST - XCOM Pair production interaction coefficient in Au A ( ) pp NAV Geant4 LowE Penelope Geant4 Standard Geant4 LowE EPDL NIST - XCOM p-value (pair production interaction coefficient test) pp p-value stability study H0 REJECTION AREA Rayleigh interaction coefficient 1 keV – 100 GeV Physics models under test: • Geant4 Low Energy – EPDL • Geant4 Low Energy – Penelope Reference data: • NIST - XCOM The Geant4 Low Energy models seem to be in disagreement with the reference data for some materials EPDL XCOM Penelope XCOM Be 0.99 1 Al 0.32 <0.05 Si 0.77 <0.05 Fe 1 <0.05 Ge <0.05 0.39 Ag 0.36 0.08 Cs <0.05 <0.05 Au <0.05 <0.05 Pb <0.05 <0.05 U <0.05 <0.05 Rayleigh interaction coefficient in Be r Geant4 LowE Penelope Geant4 LowE EPDL NIST - XCOM A ( )r NAV Rayleigh interaction coefficient The disagreement is evident between 1 keV and 1 MeV photon energies. For what concerns the Geant4 Low Energy EPDL model, the effect observed derives from an intrinsic inconsistency between Rayleigh cross section data in NIST-XCOM and the cross sections of EPDL97, on which the model is based. Differences between EPDL97 and NISTXCOM have already been highlighted in a paper by Zaidi, which recommends the Livermore photon and electron data libraries as the most up-to-date and accurate databases available for Monte Carlo modeling. Rayleigh interaction coefficient in Au r NIST A ( )r NAV EPDL 97 Zaidi H., 2000, Comparative evaluation of photon cross section libraries for materials of interest in PET Monte Carlo simulation IEEE Transaction on Nuclear Science 47 2722-35 Test of Geant4 electron processes Electron Stopping Power 10 keV – 1 GeV Physics models under test: Experimental • Geant4 Standard set-up • Geant4 Low Energy – Livermore Electrons are generated • Geant4 Low Energy – Penelope with random direction at Reference data: the center of the box • NIST ESTAR - ICRU 37 and stop inside the box CSDA: particle range without energy loss fluctuations and multiple scattering 1 dE SP ( ) dx centre p-value stability study Maximum step allowed in tracking particles was set about1/10 of the expected range value, to ensure the accuracy of the calculation The comparison test exhibited that all the Geant4 physics models are in excellent agreement with the NISTESTAR reference data. The test has not pointed out any particular difference among the three sets of models. Geant4 LowE Penelope Geant4 Standard Geant4 LowE Livermore NIST - ESTAR H0 REJECTION AREA Electron CSDA Range 10 keV – 1 GeV Physics models under test: • Geant4 Standard • Geant4 Low Energy – Livermore • Geant4 Low Energy – Penelope Reference data: • NIST ESTAR - ICRU 37 CSDA range in U Geant4 LowE Penelope Geant4 Standard Geant4 LowE Livermore NIST - ESTAR CSDA: particle range without energy loss fluctuations and multiple scattering The three Geant4 models are equivalent p-value stability study H0 REJECTION AREA Test of Geant4 proton and alpha processes Protons and alpha particles • Comparison of Geant4 models with respect to ICRU 49 protocol • Geant4 LowE Package has ICRU 49 parameterisations as one of its models verification, not validation • The Ziegler parameterisations are as authoritative as the ICRU 49 reference comparison rather than validation Protons Alpha particles Geant4 models under test: Geant4 models under test: • Standard • Low Energy – ICRU 49 • Low Energy – Ziegler 85 • Low Energy – Ziegler 2000 Reference data: NIST PSTAR – ICRU 49 • Standard • Low Energy – ICRU 49 • Low Energy – Ziegler 77 Reference data: NIST ASTAR – ICRU 49 Proton processes Stopping power: p-value stability study 1 keV – 10 GeV Stopping power in Al H0 REJECTION AREA CSDA range: p-value stability study + Geant4 LowE Ziegler 1985 Geant4 LowE Ziegler 2000 Geant4 Standard Geant4 LowE ICRU 49 NIST - PSTAR H0 REJECTION AREA Alpha particles processes 1 keV – 1 GeV CSDA range in Si Stopping power: p-value stability study Geant4 LowE Ziegler 1977 Geant4 Standard Geant4 LowE ICRU 49 NIST - ASTAR H0 REJECTION AREA The complex physics modeling of ion interactions in the low energy range is addressed by the Geant4 Low Energy package and it represented one of the main motivations for the developing of this package. Conclusions • Systematic validation of Geant4 electromagnetic models against ICRU protocols and NIST reference data • Validation based on a rigorous, quantitative statistical analysis of test results • All Geant4 electromagnetic models are found in good agreement with the reference data • Quantitative statistical analysis documents the respective strengths of the Geant4 models in detail, for each of the physics distributions considered in the NIST reference. The quantitative documentation presented provides an objective guidance to select the Geant4 electromagnetic models most appropriate to any specific simulation application. This work is a part of a wider project for the systematic validation of Geant4 electromagnetic physics models, covering also other particles types, physics processes and energy ranges outside the scope of the NIST reference data.