Geant4 Low Energy Electromagnetic Physics

1. ow Energy Electromagnetic Physics http://www.ge.infn.it/geant4/lowE/index.html S. Chauvie,G. Depaola, F. Longo, V. Ivanchenko, P. Nieminen, M.G. Pia on behalf of Geant4 Low Energy Electromagnetic Working Group Budker Inst. Novosibirsk - CERN - Univ. of Cordoba - ESA INFN (Ferrara, Genova, Torino,Trieste) CHEP 2001 Conference Beijing, 3-7 September 2001

2. Low energy e/g models in Cosmic rays, jovian electrons were triggered by astrophysics requirements 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) C, N, O line emissions included Courtesy ESA Space Environment & Effects Analysis Section

3. Dark matter searches Bepi Colombo XMM Boulby mine Courtesy of NASA/CXC/SAO Brachytherapy Radiotherapy From deep underground to galaxies AGN From crystals to human beings GLAST

4. A user a day keeps the doctor away A growing interest… • The activity on Geant4 Low Energy Electromagnetic Physics started in October 1998 • Part of the RD44 electromagnetic category, 1 ESA contractor • Continued as a subset of Geant4 general Electromagnetic Working Group (2 people) • Initially meant to be one of the “ESA modules” for space radiation studies, limited to electron and photon processes • The scope of the activity extended soon • Physics: wide set of models • Applications: also HEP, astrophysics, medical… • Independent Geant4 Low Energy Electromagnetic Working Groupcreated in April 2000 (9 members initially) • 53 members now • Contacts in progress with new people interested to collaborate 2000 2001

5. Working Group Objectives - 2001 Rigorous approach to software engineering Rich and transparent physics Goal-directed project management How we operate Physics Applications Wide spectrum of development: Team • Ample coverage of expertise (theory, experimental, software) • Emphasis on training of group members Collaboration • Promotion of cross-WG activities • Close relationship with user communities Outreach • Active strategy of information • Promotion of technology transfer

6. Software Process • A rigorous approach to software engineering • in support of a better quality of the software • especially relevant in the physics domain of Geant4-LowE EM • several mission-critical applications (space, medical…) • Public URD • Full traceability through UR/OOD/implementation/test • Testing suite and testing process • Public documentation of procedures • Defect analysis and prevention • etc.… Spiral approach A life-cycle model that is both iterative and incremental Collaboration-wide Geant4 software process, tailored to the WG projects (see talk on Geant4 Software Process by G. Cosmo) Huge effort invested into SPI • started from level 1 (CMM) • in very early stages: chaotic, left to heroic improvisation current status

7. Various methodologies adopted to capture URs User Requirements • Elicitation through interviews and surveys • 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 • Prototyping • Useful especially if requirements are unclear or incomplete • Prototype based on tentative requirements, then explore what is really wanted Posted on the WG web site • Not only functional requirements, users also ask for • Proof of validationof the physics • Documentation • Examplesof application in real-life set-ups Specification:PSS-05 standard Analysis:in WG workshops Maintenance:under configuration management User requirements evolve …and we should be able to cope with their evolution!

8. Technology as a support to physics OOAD • Rigorous adoption of OO methods •  openness to extension and evolution • Extensive use of design patterns • Booch methodology

9. Hadrons and ions Open to extension and evolution Physics models handled through abstract classes Algorithms encapsulated in objects Transparency of physics, clearly exposed to users Interchangeable and transparent access to data sets

10. Data Management Very important domain: physics models based on the use of evaluated databases Intelligent data: know how to handle themselves through algorithm objects e.g.: interpolation algorithms encapsulated in objects (to let them vary and be interchangeable) Composite pattern to treat different physical entities (e.g. whole atom and atom with shell structure) transparently

11. Photons

12. Now fluorescence is implemented only In progress/future: Auger, Coster-Kronig PIXE Atomic relaxation Domain decomposition leads to a design open to physics extensions

13. Suite of unit tests (~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 Testing Integrated with development (not “something to do at the end”) XP practice “write a test before writing the code” recommended to WG developers!

14. Photon transmission, 1mm Pb shell effects fluorescence GaAs lines Fe lines Electron and Photon processes • Validity range: 250 eV – 100 GeV • 250 eV is a “suggested” lower limit • data libraries down to 10 eV • 1 < Z < 100 • Exploit evaluated data libraries(from LLNL): • EADL (Evaluated Atomic Data Library) • EEDL (Evaluated Electron Data Library) • EPDL97 (Evaluated Photon Data Library) • for the calculation of total cross section and generation of the final state • Compton scattering • Rayleigh scattering • Photoelectric effect • Pair production • Bremsstrahlung • Ionisation • + atomic relaxation

15. Photon attenuation: comparison with NIST data Testing and Validation by IST - Natl. Inst. for Cancer Research, Genova Pb water Fe • Low Energy EM • Standard EM w.r.t. NIST data accuracy within 1% Courtesy of S. Agostinelli, R. Corvo, F. Foppiano, S. Garelli, G. Sanguineti, M. Tropeano

16. x x f hn  A hn0 10 MeV 100 keV q 1 MeV a small  z O small  small  C large  large  large  y Cross section: Polarisation Low Energy Polarised Compton Sample Methods: • Integrating over  • Sample  •  - Energy Relation  Energy • Sample of  fromP() = a (b – c cos2) distribution 250 eV -100 GeV Scattered Photon Polarization More details: talk on Geant4 Low Energy Electromagnetic Physics  Polar angle  Azimuthal angle  Polarization vector Other Low Energy Polarised Processes under development

17. Hadron and ion processes Variety of models, depending on energy range, particle type and charge Positive charged hadrons • 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 • 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 Positive charged ions • Effective charge model • Nuclear stopping power • Scaling: • 0.01 < b < 0.05 parameterisations, Bragg peak • based on Ziegler and ICRU reviews • b < 0.01: Free Electron Gas Model Negative charged hadrons • Parameterisation of available experimental data • Quantum Harmonic Oscillator Model • Model original to Geant4 • Negative charged ions: required, foreseen

18. Stopping power Z dependence for various energies Ziegler and ICRU models Ziegler and ICRU, Fe Ziegler and ICRU, Si Straggling Nuclear stopping power Bragg peak (with hadronic interactions) Some results: protons

19. protons Energy loss in Silicon antiprotons Deuterons Some results: ions and antiprotons Ar and C ions

20. Application examples • Three advanced examples developed by the LowE EM WG released in December 2000 as part of the Geant4 Toolkit (support process) • X-ray telescope • g-ray telescope • brachytherapy Full scale applications showing physics guidelines and advanced interactive facilitiesin real-life set-ups • More in progress • Underground physics and radiation background • X-ray fluorescence and PIXE Extensive collaboration with Analysis Tools groups (see talk by A. Pfeiffer, Architecture of Collaborating Frameworks)

21. Solar system explorations Cosmic rays, jovian electrons Courtesy P.Truscott, DERA RGS Courtesy of F. Foppiano, M.Tropeano, IST EPIC Courtesy SOHO EIT Solar X-rays, e, p Courtesy of R. Nartallo, ESA X-ray telescope XMM ZEPLIN III Dark Matter, Boulby mine Courtesy of S. Magni, Borexino Courtesy of A. Howard, UKDM User applications No time to mention them all! See also other talks: Simulation for astroparticle experiments (this session) From HEP computing to bio-medical research (plenary)

22. 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

23. http://www.ge.infn.it/geant4/lowE/index.html