Outline Monte Carlo Radiation Transport • Overview of radiation transport Modeling: capabilities and packages (other than MCNP), with examples capabilities and examples • New features in MCNP6 Lecture 8 • Hands-on examples – Use of VisEd Special Topics: – Make simple changes to Example files Device Modeling

Some radiation transport Introduction packages • Modern Monte Carlo modeling approach was developed in late 1940’s by Stanislav Ulam • The list is non-exhaustive working on nuclear weapons projects at LANL – ETRAN (Berger, Seltzer; NIST 1978) – EGS4 (Nelson, Hirayama, Rogers; SLAC 1985) • Coincided with development of the first electronic www.slac.stanford.edu/egs computer ENIAC (Electronic Numerical – EGS5 (Hirayama et al; KEK-SLAC 2005) Integrator And Computer) rcwww.kek.jp/research//egs5.html • Several general-purpose and specialized radiation – EGSnrc (Kawrakow and Rogers; NRCC 2000) transport packages are available www.irs.inms.nrc.ca/inms/irs/irs.html • Most are free for the academic use – Penelope (Salvat et al; U. Barcelona 1999) www.nea.fr/lists/penelope.htm

Some radiation transport Electron-Gamma Shower (EGS) packages • The Electron-Gamma Shower (EGS) computer • The list is non-exhaustive code system is a general purpose package for the – Fluka (Ferrari et al; CERN-INFN 2005) www.fluka.org Monte Carlo simulation of the coupled transport – Geant3 (Brun et al; CERN 1986) www.cern.ch of electrons and photons – (Apostolakis et al; CERN++ 1999) • Features an arbitrary geant4.web.cern.ch/geant4 geometry – MARS (James and Mokhov; FNAL) • For particles with www-ap.fnal.gov/MARS energies from a few – MCNPX/MCNP5 (LANL 1990) mcnpx.lanl.gov keV up to several TeV List by Michel Maire (Lapp/Annecy), Introduction to Monte Carlo radiation transport codes, 2016 Massive shower in a tungsten target produced by a single 10GeV incident electron; image from http://rcwww.kek.jp/research/egs/egs4_source.html

1 Electron-Gamma Shower (EGS) EGSnrc/BEAMnrc/DOSEXYZnrc • The EGS4 code can be downloaded and used by any interested party for non-commercial purposes • EGSnrc is an extended version of the EGS4 code system developed jointly by NRC and the Stanford • Disclaimer: the code is copyrighted by Stanford Linear Accelerator Center (SLAC) in the 1980s University and the Canadian government, either explicitly or implicitly • Includes a C++ geometry library for defining the geometry of complex simulation environments and • National Research Council (NRC) contributes to particle sources (e.g., medical linacs) the development and application of the Monte – The BEAMnrc/DOSXYZnrc component is an improved Carlo method in the modelling of radiation version of the original BEAM package developed by NRC transport since the early 1980s and the Univ. of Wisconsin-Madison in the 1990s (DWO Rogers et al. BEAM: A Monte Carlo code to simulate radiotherapy treatment units. Med.Phys. 22, 1995).

BEAMnrc/DOSEXYZnrc Condensed history algorithm

• Full set of photon interactions • A complete electron history, where elastic scattering events that are below • Electron transport is handled with condensed threshold energies for large energy- loss processes (shown here are the history approach, user can choose the step size Knock-on Bremsstrahlung (delta) photon setting in motion of a knock-on • Variance reduction techniques are available electron electron, and creation of • Tracking particle’s history is available bremsstrahlung photon) are replaced • Result: a phase space file (psf) at a scoring plane; with CSDA steps can be further processed with DOSEXYZ or other • The step size depends on the algorithm psf processing utility • Absorption of the primary and knock- on electrons at their track ends (based on cut-off energy)

BEAMnrc/DOSEXYZnrc BEAMnrc/DOSEXYZnrc

• Illustration of the • Widely used for MC components of a simulations of medical typical Varian linear linacs accelerator treatment • User interface tailored to head in photon beam mode building accelerator head • Phase space planes for with components simulating patient- • Parallelization capabilities dependent and patient- independent structures • Some limitations with Chetty et al.: AAPM Task Group Report No. are also represented 105: Monte Carlo-based treatment planning, DOSE respect to geometry XYZ Med. Phys. 34, 2007 , pp. 4818-4850

2 BEAMnrc capabilities GEANT 4 • Geant 4 (GEometry ANd Tracking) is a toolkit for the simulation of the passage of particles through matter; it is general-purpose by nature • Its areas of application include high energy, nuclear and accelerator physics, medical and space science • Wide range of energies and scales: very high energies (Hadron collider) to very low energies • Modeling of the Siemens ONCOR linear accelerator in 6 MV and 18 MV beams was performed. The results of simulation were validated by (DNA-extension can simulate particle-matter measurements in water by ionization chamber and extended dose range interactions in liquid water and the chemistry (EDR2) film in solid water initiated by water radiolysis; down to ~eV and nm) K. Jabbari, H. S. Anvar, et al., J Med Signals Sens. 2013, 3(3): 172–179.

GEANT 4 GEANT 4 examples

• The toolkit includes: user interfaces, built-in steering • The GAMMAKNIFE example routines, and command interpreters which operate at every simulates an advanced device level of the simulation for Stereotactic • Geant4 is written in C++ and exploits object-oriented (Leksell Gamma-Knife unit) technology; Unix, MAC, Windows are supported (involves • 60Co sources (1.25 MeV) C++ compilation even under Windows) arranged in a hemispherical • Pretty steep learning curve (for programming-inclined) 201 sources are shape, focusing on the isocenter, • Its development, maintenance and user support are taken care replaced with 1 the collimation system with 4 to by the international Geant4 Collaboration source and 18mm beam diameters rotating phantom (http://www.geant4.org/geant4/) • Spherical water phantom (r=8 cm) simulating the phantom Example from https://twiki.cern.ch/twiki/bin/view/Geant4/ AdvancedExamplesGammaknife

GEANT4-DNA examples PENELOPE Single cell irradiation by 3 MeV a- Direct DNA strand break estimation particles in a high resolution Cellular from a single 100 keV proton irradiation • PENELOPE is an acronym for "Penetration and phantom of a nucleosome ENErgy LOss of Positrons and Electrons" • A general-purpose Monte Carlo simulation code developed at the University of Barcelona • Distributed by the OECD/Nuclear Energy Agency Data Bank (Paris) and the RSICC (Oak Ridge). • More than 1,000 copies distributed • List server: http://www.oecd- nea.org/lists/penelope.html M.A. Bernala, M.C. Bordage, et al., Track structure modeling in liquid water: A review of the Geant4-DNA very low energy extension of the Geant4 Monte Carlo simulation toolkit, Physica Medica 31, 2015, pp 861–874.

3 PENELOPE PENELOPE • Main code features: • Written in Fortran, i.e., they can be run on any – Realistic, well defined interaction models, energy range from 50 eV to 109 eV operating system with a Fortran compiler – Fast and accurate random sampling algorithms • The output is formatted for visualization with the – Efficient tools for tracking particles through complex plotting program gnuplot (Windows and Linux) geometries (constructive quadric geometry) • Main applications: • Complementary tools: – Radiotherapy and Nuclear Medicine – variance reduction – Dosimetry and radiation metrology – transport of electrons and positrons in electromagnetic fields – Electron microscopy (SEM, electron-probe microanalysis) – tabulation of macroscopic interaction parameters – Detector response, x-ray generators, ...

PENELOPE PENELOPE examples Gamma-ray spectrometry with p-type HP Ge detector

What you see is what is passed to the simulation program

Geometry viewers: 2- and 3-dimensional p-type HP Ge detector, Marinelli beaker (García-Toraño, NIMA, 2005) 166mHo (Holmium) is a betta-emitter, decaying to 166Er (Erbium) with the subsequent emission of about 20 strong and well distributed gamma-rays over the energy range 50-1000 keV

PENELOPE examples FLUKA Simulation of dynamic jaws tomotherapy • FLUKA is a multi-purpose Monte Carlo code • MC model called TomoPen, which can transport a variety of particles over a based on PENELOPE code, wide energy range in complex geometries previously validated for the • The code is a joint project of INFN (National original TomoTherapy system Institute for Nuclear Physics of Italy) and CERN • Devised a comprehensive and Monte Carlo-based simulation of efficient MC-based model for • Applications in many fields of physics such as dynamic jaws tomotherapy, E. Sterpin1, Y. Chen, Q. Chen, W. Lu, T. R. Mackie, dynamic jaws-dynamic couch high energy experimental physics (up to TeV), and S. Vynckier, Med. Phys. 38, TomoTherapy treatments engineering shielding, detector and telescope 5230 (2011) • Calculation efficiency was ~8h design, cosmic ray studies, dosimetry, medical for one plan physics and

4 FLUKA FLUKA examples

• Simulations and • FLUKA evolved from a code specialized in high measurements have energy accelerators and shielding, into a been performed in the multipurpose multi-particle code successfully simplest situation of applied in a very wide range of fields and energies 192 collimators opened • Types of particles transported 63 (including and for a homogeneous water equivalent elementary particles like muons, (anti)neutrinos, FLUKA Monte Carlo simulation for the Leksell phantom hyperons), plus all kinds of heavy ions Gamma Knife Perfexion radiosurgery system: Homogeneous media, G. Battistoni, F. Cappucci, • FLUKA model was • Particle decays are modeled et al., Physica Medica, 2013, 29, pp. 656-661. successfully validated; • Transport in magnetic fields is well-handled treatment planning is the next step

New features of MCNP6 New features of MCNP6

• A new feature of the particle transport code • Three aspects of the new capability: MCNP6 is the ability to transport photons and – extension of photon transport to lower energies electrons to the new lower limits for energy cutoffs: – enhancement of the atomic relaxation processes treatment to 1 eV for photons and 10 eV for electrons – introduction of a single-event electron transport method • Numerous tally enhancements at lower energies • Explicit tracking of all charged particles in • All three of these features require new data, based magnetic fields on release 8 of ENDF/B VI (new library eprdata12, meaning Electron-Photon-Relaxation DATA, new • Multiple additional specialized features format works only in v.6)

Condensed history algorithm New features of MCNP6

• Single-event transport switch • Electron transport should never be <1 keV since – By default MCNP6 continues to transport condensed-history methods electrons by the condensed-history algorithms may rapidly collapse: at E down to 1 keV, and switches to the new single- just above 10 eV the electron can no longer lose energy event method below that energy. and only experiences a large – User control through optional 15-th entry on the number of elastic scatterings physics card: • There is not yet a fatal error phys:e 100. 13j 0.01 $ switch to single-event at 10 keV ENDF/B VI.8 electron cross sections for for this attempt, but there will atomic nitrogen, showing elastic, excitation, be in future versions of the bremsstrahlung, and ionization by individual shells code

5 Summary References • Fundamentals of the Monte Carlo method for neutral and charged • Several general-purpose and specialized particle transport, Alex F Bielajew, 2000 Monte Carlo radiation transport packages • BEAMnrc Users Manual, D.W.O. Rogers, B. Walters, I. Kawrakow, NRCC Report PIRS-0509(A)revL, 2016 are available • http://www.geant4.org/ • Most are free for the academic use • F. Salvat, J. M. Fernández-Varea, J. Sempau, PENELOPE. A code system for Monte Carlo simulation of electron and photon transport • Some have very steep learning curve • http://www.fluka.org/ • H. Grady Hughes, Quick-Start Guide to Low-Energy Photon/Electron • The trends are towards: Transport in MCNP6, MCNP6 User Notes LA–UR–12–21068, 2013-04- – Conversion to “general-purpose” packages 29 (Rev.3) • Other references are given within slides – Expanding low-energy limit

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