Geant4 phantom by j26QdXa

VIEWS: 16 PAGES: 14

									                        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


Geant4-Genova Group
     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

Geant4 Atomic Relaxation models           It is used by Geant4 packages:
    Fluorescence                               Low Energy Electromagnetic
                                               –   Photoelectric effect
    Auger electron emission
                                               –   Low Energy electron ionisation
                                               –   Low Energy proton ionisation (PIXE)
                                               –   Penelope Compton scattering
These physics models are                     Hadronic Physics
relevant to many diverse                       – Nuclear de-excitation
experimental applications                      – Radioactive decay
Geant4-Genova Group
                    Geant4 fluorescence
 Cosmic rays,                   Original motivation from astrophysics requirements
 jovian electrons

                                       X-Ray Surveys of Asteroids and Moons


                       Solar X-rays, e, p




                                                                          Geant3.21


                                                                           ITS3.0, EGS4
                            Courtesy SOHO EIT
                                                                           Geant4

Induced X-ray line emission:                                          250 keV
indicator of target composition                        C, N, O line emissions included

(~100 mm surface layer)
 Geant4-Genova Group                          Courtesy ESA Space beyond Effects Analysis Section
                                  Wide field of applicationsEnvironment & astrophysics
      Atomic Relaxation in Geant4
Two steps:

1. 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

2. 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


Geant4-Genova Group
              Modelling foundation
             in Geant4 Low Energy Electromagnetic Package


       Calculation of shell cross sections
         – Based on the EPDL97 Livermore Library for photoelectric effect
         – Based on the EEDL Livermore 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




Geant4-Genova Group
 Verification and Validation
                        of 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
Geant4-Genova Group
                  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



Geant4-Genova Group
                      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

Geant4-Genova Group
                Fluorescence - Shell-start 1

                                             Kolmogorov-
E (keV)




                                 Shell-end               p-value
                                              Smirnov D

               Geant4               5          0.0188       1

            ○ NIST                  6          0.0185       1

                                    10         0.0172       1

                                    13         0.0667       1

                                    14         0.0588       1

                                    18         0.0714       1

                                    19         0.0714       1
                            Z
      Geant4-Genova Group
         Fluorescence - Shell-start 3
                                     Kolmogorov-
                         Shell-end                 p-value
                                      Smirnov D
                            10         0.0192         1
         Geant4             11         0.0175         1
      ○ NIST                13         0.0250         1

                            14         0.0256         1

                            18         0.0294         1

                            19         0.0312         1

                            21         0.1429      0.997085

                            22         0.0588         1

Geant4-Genova Group
          Fluorescence - Shell-start 5

                                      Kolmogorov-
                          Shell-end               p-value
                                       Smirnov D

         Geant4              8          0.0147       1

      ○ NIST                 11         0.0435       1

                             13         0.0139       1

                             16         0.0204       1

                             19         0.0526       1

                             21         0.0196       1

                             24         0.0714       1


Geant4-Genova Group
          Fluorescence - Shell-start 6
                                       Kolmogorov-
                           Shell-end               p-value
                                       Smirnov D
                              8          0.0145       1

                             10          0.0588       1

                             11          0.0556       1
         Geant4
      ○ NIST                 13          0.0182       1

                             14          0.0179       1

                             16          0.0200       1

                             18          0.0667       1

                             19          0.0556       1

                             21          0.0588       1

                             22          0.0500       1
Geant4-Genova Group
                 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-Genova Group
                      Conclusions
 Systematic, quantitative validation of 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
Geant4-Genova Group

								
To top