APPLIED RADIATION PHYSICS

Transcription

1 A PRIMER IN APPLIED RADIATION PHYSICS F A SMITH Queen Mary & Westfield College, London fe World Scientific m Singapore * New Jersey London Hong Kong

2 CONTENTS CHAPTER 1 : SOURCES of RADIATION 1.1 Introduction Cosmic Rays Radioactive Sources Beta decay Gamma decay Alpha decay Neutron (fission) decay Accelerators Cockcroft-Walton generator Van de Graaff generator Cyclotron Electron linear accelerator (electron linac) Other Accelerator-Based Sources The electron synchrotron Synchrotron Radiation Polarization Coherence Emittance Neutron Sources Reactors Neutrons from charged-particle reactions Neutrons from photon-induced reactions 45 CHAPTER 2 : INTERACTIONS of CHARGED PARTICLES 2.1 Introduction Definitions of Range The transmission method The depth-dependence method Types of Charged Particle Interaction Energy Transfer in an Elastic Collision - Classical Theory Stopping Power of a Charged Particle - the Bethe Formula Mean excitation energy, The cut-off energy, E^ and restricted stopping power Theoretical Description for Light Charged Particles Interactions of Low Energy Electrons Momentum Loss of Heavy Charged Particles Coulomb Scattering of Heavy Charged Particles Inelastic Scattering of Light Particles - Radiation Loss Corrections for the inadequacy of the Born approximation Additional contribution of electron-electron bremsstrahlung.. 85 XI

3 xii CONTENTS 2.11 Consequences of Charged Particle Interactions Other secondary radiation Ionization yields 87 CHAPTER 3 : INTERACTIONS of PHOTONS 3.1 Introduction Attenuation Coefficients (linear, mass, atomic and electronic) Classical (Thomson) Scatter from a Single Electron Coherent (Rayleigh) Scatter Incoherent (Compton) Scatter The Klein-Nishina cross-section for Compton scatter Compton scatter from atomic electrons - the effect of electron binding Electron recoil energy in Compton collisions Electron momentum distributions from Compton profiles Photoelectric Absorption Characteristic X-rays and Auger electrons Pair Production 116 CHAPTER 4 : INTERACTIONS of NEUTRONS 4.1 General Considerations Classification in terms of energy Neutron Interactions Direct (potential) scattering Compound nucleus formation Partial decay lifetimes of compound nucleus states The formula for the Breit-Wigner cross-section Neutron Fields in Non-Multiplying Media Definition of flux and current density Collision dynamics Distributions in energy and angle of scatter Mean scatter angle and energy loss in a single collision Extension to multiple collisions The slowing-down energy spectrum Slowing down in hydrogen in the presence of absorption Slowing down in media heavier than hydrogen Neutron Diffusion Neutron balance equation for thermal energies Solution of elementary diffusion equation Moderation and Diffusion Agetheory Solution of the age equation for a point source and an infinite medium One-group theory 149

4 CONTENTS xiii CHAPTER 5 : DETECTORS 5.1 Introduction Gas Detectors Drift of charged species in electric fields Recombination of charge carriers of opposite sign Electron attachment Optimum conditions Ionization chambers Special applications of ionization chambers Proportional chambers Geiger-Mueller chambers Scintillation Detectors Light production mechanism in inorganic scintillators Light production mechanism in organic scintillators Efficiency of scintillation detectors Energy resolution of scintillation detectors Semiconductor Detectors Thep- n junction Germanium detectors Nuclear spectroscopy using age photon detector Microstrip and charge coupled devices Channel Electron Multipliers 196 CHAPTER 6 : MICRODOSIMETRY and RADIATION EFFECTS 6.1 Introduction Basic Definitions of the Variables Energy deposit e Specific energy imparted, z = e/m Lineal energy, y = e/l Experimental Determination of Microdosimetric Spectra Practical Considerations Primary Radiation Effects Reactions of ions (A+) Reactions of electrons Rate constants governing the time evolution of radiation products Practical determination of rate constants Track Structure Temporal considerations Spatial considerations Equipartition principle of stopping power Radiation Effects in Condensed Systems Radiolysis of Water The Fricke Dosimeter 216

5 xiv CONTENTS 6.10 Ionic Crystals Radiation Effects in Polymers Radiation Effects in Glasses Intense Irradiation of Graphite Radiation Effects in Silicon 228 CHAPTER 7 : DOSIMETRY 7.1 Definitions Charged Particle Equilibrium An inten'ace irradiated by low energy photons The build-up region for high energy radiation Photon Interaction Coefficients Relations Between Exposure, Kerma and Absorbed Dose Calculation of Specific Air Kerma Measurement of Exposure The Air-Wall Ionization Chamber Cavity Theories Bragg-Gray cavity theory Corrections to the Bragg-Gray cavity theory Practical Aspects of Ionization Chamber Dosimetry Determination of absorbed dose in a medium Temperature and pressure corrections Polarity effects Ion recombination Calorimetry Calorimetry for low energy electrons using a graphite core Other calorimeter methods Standardization Low and medium energy X-rays High energy photons ^ Co y-rays and X-rays in the range 4-19MeV) Electrons Chemical Dosimeters Thermo-Luminescence (TL) Dosimetry Solid-State Dosimeters Film Dosimetry 266 CHAPTER 8 : ACTIVATION 8.1 Introduction Basic Principles Basic Formulae Irradiation by Neutrons Activation of structural materials Activation of human tissue Radioisotope production 276

6 CONTENTS xv Neutron activation analysis (NAA) Effects of self-absorption in NAA Effects of energy-dependent cross-sections in NAA Irradiation by Charged Particles A Practical Example - The Proton Irradiation of Natural Copper 285 CHAPTER 9 : RADIOTHERAPY 9.1 Introduction Photons Geometrical factors Specification of dose ratios The effects of scattered radiation - field size and backscatter Dependence of fractional depth dose on TAR, TPR and BSF Filters, compensators and shields Orthovoltage glass tube (up to 300 ke V X-rays) Orthovoltage metal-ceramic tube The Greinacher constant-potential voltage-doubling circuit y-ray photons Linac-based MeV X-rays Depth-dose distributions Photon energy spectrum Neutron contamination of X-ray beams Electrons Determination of electron energy at depth in the phantom Bremsstrahlung contamination of electron beams Heavy Particles Protons Neutrons Negative pions Heavy ions Boron Neutron Capture Therapy (BNCT) General principles Practical implementation Modern Developments in Teletherapy Stereotactic methods Conformal therapy Portal imaging Brachytherapy Interstitial and intracavity brachytherapy The principles of the Paris system Experimental HDR brachytherapy dose distribution measurements Interstitial radiosurgery 354

7 xvi CONTENTS CHAPTER 10: IMAGING 10.1 Introduction Image Quality Spatial frequency and spatial resolution Modulation transfer function Contrast X-Ray Techniques X-ray beam modification for imaging The filtration of X-ray beams Diagnostic Radiology (DR) Film Reduction of contrast due to scatter Intensifying screens Real-time detectors for X-ray imaging Computerized Tomography (CT) Spatial resolution Contrast Radiation dose Nuclear Medicine Compartmentai analysis with radioisotope tracers Rate constants Transit times Flow rates through a single channel Flow through an organ having multiple channels Positron Emission Tomography (PET) Basic principles A 2-compartment model with reversible flow Clinical aspects in PET Magnetic Resonance Imaging Basic quantities A nuclear magnetic resonance experiment Magnetic field gradients for projection reconstruction imaging Pulse sequencing 404 CHAPTER 11 : RADIATION PROTECTION 11.1 Introduction Units and Special Parameters Equivalent dose Effective dose Background Levels Stochastic and Deterministic Effects of Radiation Radiation Carcinogenesis Dose: response relationships Effects of dose, dose-rate and LET in cancer induction 418

8 CONTENTS xvii 11.6 Maximum Permissible Levels of Exposure Practical Methods of Reducing Dose 422 INDEX 425