Low-Energy Electromagnetic Processes in P. Nieminen (ESA-ESTEC) http://www.ge.infn.it/geant4/lowE/ 20 February 2002 Geant4 Users' Workhsop, SLAC

Geant4 Users' Workhsop, SLAC Contents Introduction Electron and photon low-energy electromagnetic processes in Geant4 Hadron and ion low-energy electromagnetic processes in Geant4 Conclusions 20 February 2002 Geant4 Users' Workhsop, SLAC

Low-Energy e.m. applications Dark matter search, Fundamental physics High Energy Physics Radiotherapy, brachytherapy Neutrino physics Low-Energy e.m. applications Spacecraft internal charging analyses Radiation effects analysis in X-and g-ray astrophysical observatories Mineralogical surveys of Solar System bodies Antimatter experiments

Electron and photon processes Energy cut-offs Geant3.21 10 keV EGS4, ITS3.0 1 keV Geant4 “standard models” - Photoelectric effect 10 keV - Compton effect 10 keV - Bremsstrahlung 1 keV - Ionisation (d-rays) 1 keV - Multiple scattering 1 keV Geant4 low-energy models 250 eV 20 February 2002 Geant4 Users' Workhsop, SLAC

Geant4 Users' Workhsop, SLAC Cosmic rays, jovian electrons X-Ray Surveys of Solar System Bodies 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 20 February 2002 Geant4 Users' Workhsop, SLAC

Features of electron and photon models Validity range from 250 eV to 100 GeV Elements Z=1 to 100 Data bases: - EADL (Evaluated Atomic Data Library), - EEDL (Evaluated Electrons Data Library), - EPDL97 (Evaluated Photons Data Library) from LLNL, courtesy Dr. Red Cullen. A version of libraries especially formatted for use with Geant4 available from Geant4 distribution source. 20 February 2002 Geant4 Users' Workhsop, SLAC

Geant4 Users' Workhsop, SLAC Processes included: …in preparation: Compton scattering Photoelectric effect Rayleigh effect Pair production Bremsstrahlung Ionisation Atomic relaxation Polarised processes Auger effect Positrons New physics 20 February 2002 Geant4 Users' Workhsop, SLAC

Technology as a support to physics OOAD Technology as a support to physics Rigorous adoption of OO methods  openness to extension and evolution Extensive use of design patterns Booch methodology 20 February 2002 Geant4 Users' Workhsop, SLAC

Calculation of total cross sections where E1 and E2 are respectively the lower and higher energy for which data (s1 and s2) is available. Mean free path for a given process at energy E, with ni the atomic density of the ith element contributing to the material composition 20 February 2002 Geant4 Users' Workhsop, SLAC

Geant4 Users' Workhsop, SLAC Compton scattering Energy distribution of the scattered photon according to Klein-Nishina formula multiplied by scattering functions F(q) from EPDL97 data library. The effect of scattering function becomes significant at low energies (suppresses forward scattering) Angular distribution of the scattered photon and the recoil electron also based on EPDL97. Rayleigh effect Angular distribution: F(E,q)=[1+cos2(q)]F2(q), where F(q) is the energy-dependent form factor obtained from EPDL97. 20 February 2002 Geant4 Users' Workhsop, SLAC

Geant4 Users' Workhsop, SLAC Gamma conversion The secondary e- and e+ energies 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 Azimuthal angle generated isotropically Choice of which particle in the pair is e- or e+ is made randomly Photoelectric effect Subshell from which the electron is emitted selected according to the cross sections of the sub-shells. De-excitation via isotropic fluorescence photons; transition probabilities from EADL. 20 February 2002 Geant4 Users' Workhsop, SLAC

Geant4 Users' Workhsop, SLAC Photons 20 February 2002 Geant4 Users' Workhsop, SLAC

Electron bremsstrahlung F(x) obtained from EEDL. At high energies: Continuous energy loss Direction of the outgoing electron the same as that of the incoming one; angular distribution of emitted photons generated according to a simplified formula based on the Tsai cross section (expected to become isotropic in the low-E limit) Gamma ray production 20 February 2002 Geant4 Users' Workhsop, SLAC

Geant4 Users' Workhsop, SLAC Electron ionisation The d-electron production threshold Tc is used to separate the continuous and discrete parts of the process Partial sub-shell cross sections ss obtained by interpolation of the evaluated cross section data in the EEDL library Interaction leaves the atom in an excited state; sampling for excitation is done both for continuous and discrete parts of the process Both the energy and the angle of emission of the scattered electron and the d-ray are considered The resulting atomic relaxation treated as follow-on separate process 20 February 2002 Geant4 Users' Workhsop, SLAC

Electron ionisation Bs is the binding energy of sub-shell s Continuous energy loss Value of coefficient A for each element is obtained from fit to EEDL data for energies available in the database d-electron production 20 February 2002 Geant4 Users' Workhsop, SLAC

Geant4 Users' Workhsop, SLAC Atomic relaxation EADL data used to calculate the complete radiative and non-radiative spectrum of X-rays and electrons emitted Auger effect and Coster-Kronig effect under development; fluorescent transitions implemented Transition probabilities explicitly included for Z=6 to 100 K, L, M, N, and some O sub-shells considered. Transition probabilities for sub-shells O, P, and Q negligible (<0.1%) and smaller than the precision with which they are known For Z=1 to 5, a local energy deposit corresponding to the binding energy B of an electron in the ionised sub-shell simulated. For O, P, and Q sub-shells a photon emitted with energy B 20 February 2002 Geant4 Users' Workhsop, SLAC

Atomic relaxation Domain decomposition leads to a design open to physics extensions 20 February 2002 Geant4 Users' Workhsop, SLAC

Geant4 Users' Workhsop, SLAC 20 February 2002 Geant4 Users' Workhsop, SLAC

Geant4 Users' Workhsop, SLAC water water Photon attenuation coefficient Comparison with NIST data Standard electromagnetic package and Low Energy extensions Fe 20 February 2002 Geant4 Users' Workhsop, SLAC

Geant4 Users' Workhsop, SLAC Thorax slice CT image 6 MV photon beam Siemens KD2 Courtesy LIP and IPOFG-CROC (Coimbra delegation of the Portuguese Oncology Institute) 20 February 2002 Geant4 Users' Workhsop, SLAC

Polarised Compton Scattering y O z x q a f hn hn0  A C The Klein-Nishina cross section: Where, h0 : energy of incident photon h : energy of the scattered photon  : angle between the two polarization vectors 20 February 2002 Geant4 Users' Workhsop, SLAC

Geant4 Users' Workhsop, SLAC Angular distribution of scattered radiation composed of two components: e’|| and e’^ with respect to AOC plane e’^ e’|| C O e A hn e’ x b Q  distribution obtained with the class 20 February 2002 Geant4 Users' Workhsop, SLAC

Geant4 Users' Workhsop, SLAC Test of the distribution: a) Low energy b) High energy The distribution function is: where and  = h / h0. Low energy: ho << mc2 => h  ho =>  =1 => a = 0 the distribution reduces to the Thompson distribution => the probability that the two polarization vectors are perpendicular is zero. High energy: small  => h  ho => equal to low energy high : it is possible to demonstrate that b/(a+b) ->0, so in this case the distribution tend to be isotropic. 20 February 2002 Geant4 Users' Workhsop, SLAC

Geant4 Users' Workhsop, SLAC Results Scalar product between the two polarization vectors for three different energies. Upper histograms: Low polar angle  Lower histograms: High polar angle  100 keV 1 MeV 10 MeV These distributions are in agreement with the limits obtained previously. 20 February 2002 Geant4 Users' Workhsop, SLAC

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 PIXE included 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 Model original to Geant4 Negative charged ions: required, foreseen Parameterisation of available experimental data Quantum Harmonic Oscillator Model 20 February 2002 Geant4 Users' Workhsop, SLAC

Geant4 Users' Workhsop, SLAC HERMES X-Ray Spectrometer on Mercury Planetary Orbiter PIXE from solar proton events 20 February 2002 Geant4 Users' Workhsop, SLAC

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 20 February 2002 Geant4 Users' Workhsop, SLAC Interchangeable and transparent access to data sets

Hadron and ion low-energy e.m. extensions Low energy hadrons and ions models based on Ziegler and ICRU data and parameterisations Barkas effect: models for antiprotons 20 February 2002 Geant4 Users' Workhsop, SLAC

Proton energy loss in H2O Ziegler and ICRU parameterisations 20 February 2002 Geant4 Users' Workhsop, SLAC

Geant4 Users' Workhsop, SLAC Application examples Five advanced examples developed by the LowE EM WG released as part of the Geant4 Toolkit (support process) X-ray telescope g-ray telescope Brachytherapy Underground physics & radiation background X-ray fluorescence and PIXE GaAs lines Fe lines fluorescence Full scale applications showing physics guidelines and advanced interactive facilities in real-life set-ups Extensive collaboration with Analysis Tools groups 20 February 2002 Geant4 Users' Workhsop, SLAC

Geant4 Users' Workhsop, SLAC Conclusions A set of models has been developed to extend the Geant4 coverage of electromagnetic interactions of photons and electrons down to 250 eV, and of hadrons down to < 1 keV Rigorous software process applied Wide user community in astrophysics, space applications, medical field, HEP, in the U.S., Europe, and elsewhere Modularity of Geant4 enables easy extensions and implementation of new models Further low-energy electromagnetic physics developments and refinements are underway 20 February 2002 Geant4 Users' Workhsop, SLAC

Geant4 Users' Workhsop, SLAC Useful links http://www.ge.infn.it/geant4/lowE/ http://www.llnl.gov/cullen1/ http://www.icru.org/pubs.htm 20 February 2002 Geant4 Users' Workhsop, SLAC