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Maria Grazia Pia, INFN Genova Low Energy Electromagnetic Physics Maria Grazia Pia INFN Genova on behalf of Geant4 Low.

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Presentation on theme: "Maria Grazia Pia, INFN Genova Low Energy Electromagnetic Physics Maria Grazia Pia INFN Genova on behalf of Geant4 Low."— Presentation transcript:

1 Maria Grazia Pia, INFN Genova Low Energy Electromagnetic Physics Maria Grazia Pia INFN Genova on behalf of Geant4 Low Energy Electromagnetic Working Group Monte Carlo 2005 Chattanooga, April 2005

2 Maria Grazia Pia, INFN Genova Boulby mine Courtesy of NASA/CXC/SAO Bepi Colombo Radiotherapy Brachytherapy Dark matter searches XMM From deep underground to galaxies From crystals to human beings Radiobiology

3 Maria Grazia Pia, INFN Genova Low Energy Electromagnetic Physics A set of processes extending the coverage of electromagnetic interactions in Geant4 down to “low” energy –250/100 eV (in principle even below this limit) for electrons and photons –down to approximately the ionisation potential of the interacting material for hadrons and ions Processes based on detailed models –shell structure of the atom –precise angular distributions Specialised models depending on particle type –data-driven models based on the Livermore Libraries for e - and photons –analytical models for e +, e - and photons (reengineering Penelope into Geant4) –parameterised models for hadrons and ions (Ziegler 1977/1985/2000, ICRU49) –original model for negative hadrons

4 Maria Grazia Pia, INFN Genova The process in a nutshell Rigorous 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 availability of resources –Limited by availability 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

5 Maria Grazia Pia, INFN Genova User requirements User Requirements Posted on the WG web site Elicitation through interviews and surveys l useful to ensure that UR are complete and there is wide agreement Joint workshops with user groups Use cases Analysis of existing Monte Carlo codes Study of past and current experiments Direct requests from users to WG coordinators Various methodologies adopted to capture URs

6 Maria Grazia Pia, INFN Genova OOAD Rigorous adoption of OO methods openness to extension and evolution Technology as a support to physics

7 Maria Grazia Pia, INFN Genova Testing Suite of unit tests (at least 1 per class) Cluster testing 3 integration/system tests Suite of physics tests (in progress with publications) Regression testing Testing process ­Testing requirements ­Testing procedures ­etc. Physics validation XP practice “write a test before writing the code” recommended to WG developers! Integrated with development (not “something to do at the end”)

8 Maria Grazia Pia, INFN Genova Photons and electrons: processes based on the Livermore library Based on evaluated data libraries from LLNL: –EADL (Evaluated Atomic Data Library) –EEDL (Evaluated Electrons Data Library) –EPDL97 (Evaluated Photons Data Library)  especially formatted for Geant4 distribution (courtesy of D. Cullen, LLNL) Validity range: 250 eV GeV –The processes can be used down to 100 eV, with degraded accuracy –In principle the validity range of the data libraries extends down to ~10 eV Elements Z=1 to Z=100 –Atomic relaxation: Z > 5 (transition data available in EADL)

9 Maria Grazia Pia, INFN Genova Calculation of cross sections E 1 and E 2 are the lower and higher energy for which data (  1 and  2 ) are available n i = atomic density of the i th element contributing to the material composition Interpolation from the data libraries: Mean free path for a process, at energy E:

10 Maria Grazia Pia, INFN Genova Photons

11 Compton scattering Energy distribution of the scattered photon according to the Klein-Nishina formula, multiplied by scattering function F(q) from EPDL97 The effect of scattering function becomes significant at low energies –suppresses forward scattering Angular distribution also based on EPDL97 Klein-Nishina cross section: Rayleigh scattering Angular distribution: F(E,q)=[1+cos 2 (q)]  F 2 (q) –where F(q) is the energy-dependent form factor obtained from EPDL97

12 Maria Grazia Pia, INFN Genova Photoelectric effect Cross section –Integrated cross section (over the shells) from EPDL + interpolation –Shell from which the electron is emitted selected according to EPDL Final state generation –Direction of emitted electron = direction of incident photon –Improved angular distribution in preparation Deexcitation via the atomic relaxation sub-process –Initial vacancy + following chain of vacancies created  conversion Pair and triplet production cross sections The secondary e - and e + energies are sampled using Bethe-Heitler cross sections with Coulomb correction e - and e + assumed to have symmetric angular distribution Energy and polar angle sampled w.r.t. the incoming photon using Tsai differential cross section

13 Maria Grazia Pia, INFN Genova Polarisation 250 eV -100 GeV y O z x     h h   A C  Polar angle  Azimuthal angle  Polarization vector More details: talk on Geant4 Low Energy Electromagnetic Physics Other polarised processes under development Cross section: Scattered Photon Polarization 10 MeV small large 100 keV small large 1 MeV small large Low Energy Polarised Compton

14 Maria Grazia Pia, INFN Genova Electron Bremsstrahlung Parameterisation of EEDL data –16 parameters for each atom –At high energy the parameterisation reproduces the Bethe-Heitler formula –Precision is ~ 1.5 % Plans –Systematic verification over Z and energy

15 Maria Grazia Pia, INFN Genova Bremsstrahlung Angular Distributions Three LowE generators available in GEANT4: G4ModifiedTsai, G4Generator2BS and G4Generator2BN G4Generator2BN allows a correct treatment at low energies (< 500 keV)

16 Maria Grazia Pia, INFN Genova Electron ionisation Parameterisation based on 5 parameters for each shell Precision of parametrisation is better then 5% for 50 % of shells, less accurate for the remaining shells Work in progress to improve the parameterisation and the performance

17 Maria Grazia Pia, INFN Genova Processes à la Penelope The whole physics content of the Penelope Monte Carlo code has been re-engineered into Geant4 (except for multiple scattering) –processes for photons: release 5.2, for electrons: release 6.0 Physics models by F. Salvat et al. Power of the OO technology: –extending the software system is easy –all processes obey to the same abstract interfaces –using new implementations in application code is simple Profit of Geant4 advanced geometry modeling, interactive facilities etc. – same physics as original Penelope

18 Maria Grazia Pia, INFN Genova Hadrons and ions Variety of models, depending on –energy range –particle type –charge Composition of models across the energy range, with different approaches –analytical –based on data reviews + parameterisations Specialised models for fluctuations Open to extension and evolution

19 Maria Grazia Pia, INFN Genova Algorithms encapsulated in objects Physics models handled through abstract classes Hadrons and ions Interchangeable and transparent access to data sets Transparency of physics, clearly exposed to users

20 Maria Grazia Pia, INFN Genova Hadron and ion processes Variety of models, depending on energy range, particle type and charge Bethe-Bloch model of energy loss, E > 2 MeV 5 parameterisation models, E < 2 MeV ­ based on Ziegler and ICRU reviews 3 models of energy loss fluctuations ­ Density correction for high energy ­ Shell correction term for intermediate energy ­ Spin dependent term ­ Barkas and Bloch terms ­ Chemical effect for compound materials ­ Nuclear stopping power Positive charged hadrons Positive charged ions Negative charged hadrons Scaling: 0.01 <  < 0.05 parameterisations, Bragg peak ­ based on Ziegler and ICRU reviews  < 0.01: Free Electron Gas Model Parameterisation of available experimental data Quantum Harmonic Oscillator Model ­ Effective charge model ­ Nuclear stopping power ­ Model original to Geant4 ­ Negative charged ions: required, foreseen

21 Maria Grazia Pia, INFN Genova Some results: protons Straggling Stopping power Z dependence for various energies Ziegler and ICRU models Ziegler and ICRU, FeZiegler and ICRU, Si Nuclear stopping power Bragg peak (with hadronic interactions)

22 Maria Grazia Pia, INFN Genova Positive charged ions Scaling: 0.01 <  < 0.05 parameterisations, Bragg peak ­ based on Ziegler and ICRU reviews  < 0.01: Free Electron Gas Model ­ Effective charge model ­ Nuclear stopping power Deuterons

23 Maria Grazia Pia, INFN Genova Models for antiprotons  > 0.5Bethe-Bloch formula 0.01 <  < 0.5Quantum harmonic oscillator model  < 0.01Free electron gas model Proton G4 Antiproton Antiproton from Arista et. al Antiproton exp. data Proton G4 Antiproton Antiproton from Arista et. al Antiproton exp. data

24 Maria Grazia Pia, INFN Genova Atomic relaxation See next talk

25 Maria Grazia Pia, INFN Genova Geant4 validation vs. NIST database All Geant4 physics models of electrons, photons, protons and  compared to NIST database –Photoelectric, Compton, Rayleigh, Pair Production cross-sections –Photon attenuation coefficients –Electron, proton,  stopping power and range Comparison of Geant4 Standard and Low Energy Electromagnetic packages against NIST reference data –document the respective strengths of Geant4 electromagnetic models Quantitative comparison –Statistical goodness-of-fit tests See talk by B. Mascialino on Wednesday

26 Maria Grazia Pia, INFN Genova Electrons: dE/dx Ionisation energy loss in various materials Compared to Sandia database More systematic verification planned Also Fe, Ur

27 Maria Grazia Pia, INFN Genova The problem of validation: finding reliable data Note: Geant4 validation at low energy is not always easy experimental data often exhibit large differences! Backscattering low energies - Au

28 Maria Grazia Pia, INFN Genova Applications A small sample in the next slides –various talks at this conference concerning Geant4 Low Energy Electromagnetic applications Many valuable contributions to the validation of LowE physics from users all over the world –excellent relationship with our user community

29 Maria Grazia Pia, INFN Genova M.Piergentili, INFN Genova LINAC for IMRT Kolmogorov-Smirnov Test: p-value=1 Kolmogorov-Smirnov Test: p-value=

30 Maria Grazia Pia, INFN Genova MicroSelectron-HDR source Dosimetry Endocavitary brachytherapy Dosimetry Endocavitary brachytherapy Dosimetry Superficial brachytherapy Dosimetry Superficial brachytherapy Leipzig applicator Dosimetry Interstitial brachytherapy Dosimetry Interstitial brachytherapy Bebig Isoseed I-125 source

31 Maria Grazia Pia, INFN Genova Hadrontherapy beam line at INFN-LNS, Catania G.A.P. Cirrone, G. Cuttone, INFN LNS

32 Maria Grazia Pia, INFN Genova Bepi Colombo Mission 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)

33 Maria Grazia Pia, INFN Genova Shielding in Interplanetary Space Missions Aurora Programme Dose in astronaut resulting from Galactic Cosmic Rays Fe - 52 Si - 28 O - 16 C - 12 p GCR (all ion components)  ESA REMSIM Project

34 Maria Grazia Pia, INFN Genova Conclusions New physics domain in HEP simulation Wide interest in the user community A wealth of physics models A rigorous approach to software engineering Significant results from an extensive validation programme A variety of applications in diverse domains


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