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Validation of

Validation of. Atomic Relaxation against the NIST reference data. Susanna Guatelli, Alfonso Mantero, Barbara Mascialino, Maria Grazia Pia, Valentina Zampichelli INFN Genova, Italy IEEE Nuclear Science Symposium San Diego, 30 October – 4 November 2006.

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Validation of

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  1. Validation of Atomic Relaxation against the NIST reference data Susanna Guatelli, Alfonso Mantero, Barbara Mascialino, Maria Grazia Pia, Valentina Zampichelli INFN Genova, Italy IEEE Nuclear Science Symposium San Diego, 30 October – 4 November 2006

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

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

  10. Fluorescence - Shell-start 3  Geant4 ○ NIST

  11. Fluorescence - Shell-start 5  Geant4 ○ NIST

  12. Fluorescence - Shell-start 6  Geant4 ○ NIST

  13. 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

  14. Conclusions • Systematic,quantitative validationof Geant4 Atomic Relaxation • Rigorous statistical methods to compare Geant4 models to reference data • Comparison against NIST experimental data • Authoritative reference, recent review paper for X-ray transition energies • Fluorescence • Analysis completed • Excellent agreement of Geant4 models with NIST data • Auger electron emission • Analysis in progress Geant4 simulates X-ray fluorescence very precisely

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