Low Energy EM P hysics Overview & status 16 th Geant4 Collaboration Workshop September 19-23, 2011, SLAC, USA Sébastien Incerti - CNRS/IN2P3/Bordeaux U., France - on behalf of the Electromagnetic Physics working groups of the Geant4 collaboration

Outline 2  Brief summary of developments since previous collaboration meeting  Highlights on  Geant4-DNA (ESA AO 6041+ANR Geant4-DNA) Physics Chemistry Biology  Polarized photon processes  Perspectives  General  Electron processes  Microdosimetry in Si

Summary of recent developments 3

Geant  Livermore Physics  New models for pair production in the electric field of the electron G4BoldyshevTripletModel and G4LivermoreNuclearGammaConversionModel  Penelope Physics  First upgrade to Penelope 2008 models  Geant4-DNA (liquid water)  Electron attachment and vibrational excitation processes and models  Extended coverage of Champion elastic scattering model for electrons down to 4 eV  New excitation model for neutral hydrogen  Preliminary discrete ionisation models for C, N, O, Fe  Multi-scale combination of Standard/Livermore/Geant4-DNA processes

Geant4 9.5 BETA 5  Penelope2008 models become default Penelope models  New common atomic deexcitation interface is available to both EM categories  Livermore: photoelectric, Compton, ionisation  Penelope: photoelectric, Compton  Geant4-DNA: ionisation  Switched msc in Physics builders to Urban 95  Migration of Physics builders to the non-numbered scheme  Coverity warnings in lowenergy and dna categories  None in ref-07  Some more in ref-08 ! Refer to talk by Luciano See talk by Alfonso today

New atomic deexcitation web page  Accessible from the web page of the LowE EM WG  Explains to users  How to include fluorescence, Auger emission & PIXE in Standard & LowE EM physics, including Geant4-DNA first time in Geant4 history Photoelec., Compton, ionization processes  How to use UI commands & EM options for activation and selection of ionisation cross section models  Refers to TestEm5 6 See talk by Alfonso today

New migration web page  All G4LowEnergy* classes have been fully removed from SVN since early August  These obsolete classes are not used anymore (flaws) in Geant4 and should not be used  Warnings in obsolete classes active since 9.3 BETA…  Explains to users how to use the upgraded Livermore and Penelope models in a PhysicsList instead of obsolete Livermore models  Suggests usage of Physics builders 7

Physics stage : processes & models Geant4-DNA 8

How can Geant4-DNA model radiation biology ? 9 Physics stage step-by-step modelling of physical interactions of incoming & secondary ionising radiation with biological medium (liquid water) Physics stage step-by-step modelling of physical interactions of incoming & secondary ionising radiation with biological medium (liquid water) Physicochemistry/chemistry stage Radical species production Diffusion Mutual interactions Physicochemistry/chemistry stage Radical species production Diffusion Mutual interactions Geometry stage DNA strands, chromatin fibres, chromosomes, whole cell nucleus, cells… for the prediction of damages resulting from direct and indirect hits Geometry stage DNA strands, chromatin fibres, chromosomes, whole cell nucleus, cells… for the prediction of damages resulting from direct and indirect hits Excited water molecules Ionised water molecules Solvated electrons Biology stage DIRECT DNA damages Biology stage INDIRECT DNA damages low LET) t=0t= st=10 -6 s

Overview of current physics models  Electrons  Elastic scattering Screened Rutherford and Brenner-Zaider below 200 eV Champion’s approach (partial wave framework, 3 contributions to the interaction potential)  Ionisation 5 levels for H 2 O Dielectric formalism & FBA using Heller optical data up to 1 MeV, and low energy corrections  Excitation 5 levels for H 2 O Dielectric formalism & FBA using Heller optical data and semi-empirical low energy corrections  Vib. Excitation Michaud et al. xs measurements in amorphous ice Factor 2 to account for phase effect  Dissociative attachment Melton et al. xs measurements  Protons & H  Excitation Miller & Green speed scaling of e - excitation at low energies and Born and Bethe theories above 500 keV  Ionisation Rudd semi-empirical approach by Dingfelder et al. and Born and Bethe theories & dielectric formalism above 500 keV (relativistic + Fermi density)  Charge change Analytical parametrizations by Dingfelder et al.  He 0, He +, He 2+  Excitation and ionisation Speed and effective charge scaling from protons by Dingfelder et al.,  Charge change Semi-empirical models from Dingfelder et al.  C, N, O, Fe  Ionisation Speed scaling and global effective charge by Booth and Grant 10 Med. Phys. 37 (2010) 4692 Appl. Radiat. Isot. 69 (2011) 220

Development of new proton single elastic scattering in liquid water  Missing proton/He elastic scattering model in Geant4-DNA  Can not be neglected below ~10 keV  In development by C. Champion et al.  Spherical symmetric potential only dependent on target charge + screening effect from target electrons  Expected to be released in Spring Champion et al. NIMB (2011) in press Champion et al. NIMB (2011) in press

Theoretical quantum cross section model reaches 10 meV Based on the theoretical work of C. Champion et al. in the partial wave framework and with a spherical potential includes three distinct terms: a static contribution and two fine correction terms corresponding to the correlation-polarization and the exchange interactions Electron elastic scattering extended down to VLE 12 Champion et al. NIMB (2011) in press Champion et al. NIMB (2011) in press

Obtained with the C. Champion elastic scattering model (down to 4 eV) Compared to ICRU recommendations and to penetration MC calculations by Meesungnoen et al. (with recommendation of including a factor 2 on elastic and vib. excitation cross sections measured in ice) Electron range, projected range and penetration BETA

Physics stage : examples Geant4-DNA 14

Examples related to Geant4-DNA 15 Example code name PurposeLocationAvailability dnaphysics Usage of Geant4-DNA Physics processes variable density Auger emission $G4INSTALL/examples/advan ced from Geant4 9.5 BETA microdosimetry Combination of Standard EM or Low Energy EM processes with Geant4-DNA Physics processes $G4INSTALL/examples/advan ced from Geant4 9.5 BETA TestEm12 Energy deposition profiles in spherical shells $G4INSTALL/examples/exten ded from Geant4 9.5 BETA

Located in $G4INSTALL/examples/advanced Region A : activation of Geant4 Standard EM processes Region B : activation of Geant4-DNA processes the user can select the energy threshold separating Standard and DNA processes « microdosimetry » advanced example 16 Incident 10 MeV proton 100 µm Ivantchenko et al. PNST (2011) in press Ivantchenko et al. PNST (2011) in press

Combination of photon models with Geant4-DNA electron models  Geant4-DNA has no specific photon processes  Thanks to the common design (Standard / Low Energy / Geant4-DNA), it becomes possible to combine photon processes (Standard, Livermore, Penelope) with Geant4-DNA electron processes 17

Chemistry stage Geant4-DNA 18

Molecular species & reactions 19 Molecular species & diffusionChemical reactions For this prototype software, we followed the set of parameters published by the authors of the PARTRAC state-of-the-art software. See talk by Mathieu

tracking of sub-thermalization electrons down to 25 meV: step-by-step tracking of sub-excitation electrons or single step using Meesungnoen fit to thermalization distance and random direction Effect of the two alternative electron elastic scattering models Comparison to results for incident 1 MeV electrons in 1 mm 3 water volume simulated by PARTRAC and Uehara and Nikjoo. Radiochemical yields: prototype results 20 ● OH radicals Solvated electrons e aq M. Karamitros et al., PNST (2011) in press See talk by Mathieu 20

Biology stage Geant4-DNA 21

The direct total strand break (TSB) yield is the number of DNA strand breaks directly produced by the ionizing particles per unit dose and base pair [(GyGbp)-1]. The TSB has been reported to be independent of the LET and type of radiation Can we explain why using Geant4-DNA ? Investigation of TSB invariance 22 M. Bernal et al., Med Phys 38 (2011) fragments of 30-nm chromatin fiber were put into a cylindrical shell (ROI) with a central diameter and height of 10 µm and 5.25 µm, respectively.

The site-hit probability per unit dose is statistically independent of the type and energy of the incident particle and energy, within ± 0.02 The ratio between the total volume occupied by the targets and that defined by the ROI is and explains the site-hit probability value TSB invariance MeV protons Secondary e-

Slides provided by Gerardo Depaola Famaf, Argentina Francesco Longo INFN Trieste, Italy Polarized photons 24

New developments  Polarized “triple” gamma conversion Simulation of the pair production by linearly polarized gamma rays on electrons Promising process to measure polarization of high energy gamma rays (astrophysics)  Radiative correction applied to pair production  Status  Beta version exist for corrected classes  On test until end of September  To be committed early October Courtesy of G. Depaola & F. Longo 25

p 1 momentum of electron recoil p 0 threshold for the momentum recoil detection X 0 = q 2 = (p 0 – p 1 ) 2 4-momentum transfer Our cross section can be compared with that obtained by Boldyshev et al. (Phys. Part. Nucl. 25, 3 (1994)). In that work, the table 5 (last column) was obtained by numerical integration of exact cross section. We found that the total cross section with momentum recoil threshold is independent of the photon energy indicating that as the photon energy increases, the process only generates electron with very low momentum recoil or, the number of electron recoils detected is constant. 1) Threshold for the momentum recoil detection in pair production by gamma-rays on electrons (“triple” production) Probability to have a recoil electron with momentum greater than a threshold defined by the user: M.L. Iparraguirre & G.O. Depaola, EPJ (2011) Courtesy of G. Depaola & F. Longo 26

2) Radiative corrections in pair production : energy distribution of the positron Courtesy of G. Depaola & F. Longo 27

This graph shows the main terms contributing to the radiative correction and the correction itself δP. Courtesy of G. Depaola & F. Longo δP

Perspectives 29

Low Energy EM perspectives for  Physics  Further extension of atomic deexcitation (« à la Penelope »)  Models for electron microdosimetry in Si  Geant4-DNA deliveries  Verification & validation of polarized electron & photon processes  Misc  Systematic validation effort for each reference tag Following Standard EM philosophy Results will be stored on /afs Livermore, Penelope: DPK, test67…  Finalize paper on verification of ranges for electrons, protons and alphas initiated by Christina Zacharatou  Review documentation + web site

Geant4-DNA deliveries 31  By 2012  Inclusion of processes & models for biological material Alternative models for liquid water New models for A, T, G, C, sugar-phosphate  Inclusion of nuclear stopping for p & He  Upgrade usage of ions  Upgrade of prototype of water radiochemistry classes  Delivery of prototype of cell geometry including DNA bases  Mid-term  Prediction of direct and non-direct DNA damages in cell nuclei  Verification (with other codes) and validation (with experimental data)

Slides provided by Paul Guèye Hampton U., VA, USA Perspectives : polarized e - / γ 32

Experimental Status I Polarized photons ① ② Benchmark data for Geant4 a) Polarized photons in water b) Energies: 200 keV to 30 MeV ③ Thesis (Hampton University) a) Rachel Black, MS b) Fall 2011 ④ Additional work a) Polarized electrons in water b) Energies: 200 keV to 30 MeV Hampton University Eastern Virginia Medical School Courtesy of P. Guèye 33

Experimental Status II Polarized electrons for polarized positrons ① ② Benchmark data for Geant4 (2-8 MeV) in Tungsten a) Polarized Bremsstrahlung process for e - b) Transfer polarization in pair production ③ Thesis (Hampton University) a) Adeleke Adeyemi, PhD b) Fall 2012 ④ Site: http//positron.jlab.org ⑤ Period (A rating: Jlab/PAC38 – Summer 2011) a) Fall 2011: commissioning + preliminary data b) Spring 2012: data taking Jefferson Lab Courtesy of P. Guèye 34

Experimental Status III Low Energy Linear Accelerator (LELIA) ① Location a) Hampton University b) Validation machine for Geant4 low energy electromagnetic physics ② Electrons beams (1.5 MHz, ~100  A to few mA, tunable) a) 100 keV: Fall 2011 b) 500 keV: Fall 2012 c) 5 MeV: Fall 2013 ③ Benchmark data for Geant4 a) Unpolarized e - b) Transmission, multiple scattering, bremsstrahlung… ④ Thesis (University Cheikh Anta Diop) a) Fatou Ndoye, PhD b) Spring 2013 Courtesy of P. Guèye 35

Slides provided by Mélanie Raine CEA, France Perspectives Microdosimetry models for Si 36

37 Model implementation  Cross-sections calculation  Inelastic model similar to the one used in Geant4-DNA The model has been validated for electrons (see A. Valentin et al., NSS 2010) and for protons (to be published) The ion cross-sections are deduced from the proton cross-section by scaling  Elastic cross-sections extracted from the ICRU database  New Geant4 model classes  Based on Geant4-DNA in Geant4.9.3 PhysicsList Inelastic processElastic process Inelastic modelElastic model Data Si atomic structure Courtesy of M. Raine A. Valentin et al., NSS 2010 Proc. (2011)

38 Some results Livermore modelOur model 10 keV electrons 10 MeV protons Target: 10 µm cube Electron ranges To be published Courtesy of M. Raine 38

39 What’s next  Debugging: in some cases, the ion mass and charge are not correctly obtained and the scaling fails  After this last debug and upgrade to Geant4 9.5, the classes will be ready to be delivered  next Spring  A user example has been prepared  Solutions to enhance the model accuracy are under study  For technical details, please contact   Courtesy of M. Raine

Thanks for your attention 40