MEASUREMENT AND DETECTION OF RADIATION

Transcription

1 MEASUREMENT AND DETECTION OF RADIATION Second Edition Nicholas Tsoulfanidis University of Missouri-Rolla Ж Taylor &Francis * Publishers since I79H

2 CONTENTS Preface to the First Edition Preface to the Second Edition xvii xxi 1 INTRODUCTION TO RADIATION MEASUREMENTS What is Meant by Radiation? Statistical Nature of Radiation Emission The Errors and Accuracy and Precision of Measurements Types of Errors Nuclear Instrumentation Introduction The Detector The NIM Concept The High-Voltage Power Supply The Preamplifier The Amplifier The Oscilloscope The Discriminator or Single-Channel Analyzer (SCA) The Scaler The Timer The Multichannel Analyzer 21 Bibliography 21 Reference 21 2 STATISTICAL ERRORS OF RADIATION COUNTING Introduction Definition of Probability Basic Probability Theorems Probability Distributions and Random Variables 28

3 viii CONTENTS 2.5 Location Indexes (Mode, Median, Mean) Dispersion Indexes, Variance, and Standard Deviation Covariance and Correlation The Binomial Distribution The Poisson Distribution The Normal (Gaussian) Distribution The Standard Normal Distribution Importance of the Gaussian Distribution for Radiation Measurements The Lorentzian Distribution The Standard, Probable, and Other Errors The Arithmetic Mean and Its Standard Error Confidence Limits Propagation of Errors Calculation of the Average and Its Standard Deviation Examples of Error Propagation Uncorrelated Variables Goodness of Data x 2 Criterion Rejection of Data The Statistical Error of Radiation Measurements The Standard Error of Counting Rates Combining Counting Rates Methods of Error Reduction The Background Is Constant and There Is No Time Limit for Its Measurement There Is a Fixed Time Г Available for Counting Both Background and Gross Count Calculation of the Counting Time Necessary to Measure a Counting Rate with a Predetermined Statistical Error Relative Importance of Error Components Minimum Detectable Activity Counter Dead-Time Correction and Measurement of Dead Time 73 Problems 76 Bibliography 78 References 78 REVIEW OF ATOMIC AND NUCLEAR PHYSICS Introduction Elements of Relativistic Kinematics Atoms Nuclei Nuclear Binding Energy Nuclear Energy Levels Energetics of Nuclear Decays Gamma Decay Alpha Decay Beta Decay Particles, Antiparticles, and Electron-Positron Annihilation Complex Decay Schemes The Radioactive Decay Law

4 CONTENTS ix 3.9 Nuclear Reactions General Remarks Kinematics of Nuclear Reactions Fission 113 Problems 117 Bibliography 119 References ENERGY LOSS AND PENETRATION OF RADIATION THROUGH MATTER Introduction Mechanisms of Charged-Particle Energy Loss Coulomb Interactions Emission of Electromagnetic Radiation (Bremsstrahlung) Stopping Power Due to Ionization and Excitation Energy Loss Due to Bremsstrahlung Emission Calculation of de/dx for a Compound or Mixture Range of Charged Particles Range of Heavy Charged Particles (p, d, t, a; 1 < A < 4) Range of Electrons and Positrons Transmission of Beta Particles Energy Loss after Traversing a Material of Thickness t < R Stopping Power and Range of Heavy Ions (Z > 2, A > 4) Introduction The de/dx Calculation Range of Heavy Ions Interactions of Photons with Matter The Photoelectric Effect Compton Scattering or Compton Effect Pair Production Total Photon Attenuation Coefficient Photon Energy Absorption Coefficient Buildup Factors Interactions of Neutrons with Matter Types of Neutron Interactions Neutron Reaction Cross Sections The Neutron Flux Interaction Rates of Polyenergetic Neutrons 172 Problems 173 Bibliography 174 References GAS-FILLED DETECTORS Introduction Relationship Between High Voltage and Charge Collected Different Types of Gas-Filled Detectors 180

5 X CONTENTS 5.4 Ionization Chambers Pulse Formation in an Ionization Chamber Current Ionization Chambers Proportional Counters Gas Multiplication in Proportional Counters The Pulse Shape of a Proportional Counter The Change of Counting Rate with High Voltage The High-Voltage Plateau Geiger-Müller Counters Operation of a GM Counter and Quenching of the Discharge The Pulse Shape and the Dead Time of a GM Counter Gas-Flow Counters The Long-Range Alpha Detector (LRAD) Internal Gas Counting Rate Meters General Comments about Construction of Gas-Filled Detectors 208 Problems 209 Bibliography 209 References SCINTILLATION DETECTORS Introduction Inorganic (Crystal) Scintillators The Mechanism of the Scintillation Process Time Dependence of Photon Emission Important Properties of Certain Inorganic Scintillators Organic Scintillators The Mechanism of the Scintillation Process Organic Crystal Scintillators Organic Liquid Scintillators Plastic Scintillators Gaseous Scintillators The Relationship Between Pulse Height and Energy and Type of Incident Particle The Response of Inorganic Scintillators The Response of Organic Scintillators The Photomultiplier Tube General Description Electron Multiplication in a Photomultiplier Assembly of a Scintillation Counter and the Role of Light Pipes Dead Time of Scintillation Counters Sources of Background in a Scintillation Counter The Phoswich Detector 232 Problems 233 Bibliography 233 References 234

6 CONTENTS xi 7 SEMICONDUCTOR DETECTORS Introduction Electrical Classification of Solids Electronic States in Solids-The Fermi Distribution Function Insulators Conductors Semiconductors The Change of the Energy Gap with Temperature Conductivity of Semiconductors Extrinsic and Intrinsic Semiconductors The Role of Impurities The p-n Junction The Formation of a p-n Junction The p-n Junction Operating as a Detector The Different Types of Semiconductor Detectors Surface-Barrier Detectors Diffused-Junction Detectors Silicon Lithium-Drifted [Si(Li)] Detectors Germanium Lithium-Drifted [Ge(Li)] Detectors Germanium (Ge) Detectors CdTe and Hgl 2 Detectors Radiation Damage to Semiconductor Detectors 260 Problems 261 Bibliography 262 References RELATIVE AND ABSOLUTE MEASUREMENTS Introduction Geometry Effects The Effect of the Medium between Source and Detector The Solid Angle General Definition The Solid Angle for a Point Isotropic Source and a Detector with a Circular Aperture The Solid Angle for a Disk Source Parallel to a Detector with a Circular Aperture The Solid Angle for a Point Isotropic Source and a Detector with a Rectangular Aperture The Solid Angle for a Disk Source and a Detector with a Rectangular Aperture The Use of the Monte Carlo Method for the Calculation of the Solid Angle Source Effects Source Self-Absorption Factor (f a ) Source Backscattering Factor (f b ) Detector Effects Scattering and Absorption Due to the Window of the Detector Detector Efficiency (e) 283

7 xii CONTENTS Determination of Detector Efficiency Relationship Between Counting Rate and Source Strength 287 Problems 289 References INTRODUCTION TO SPECTROSCOPY Introduction Definition of Energy Spectra Measurement of an Integral Spectrum with a Single-Channel Analyzer Measurement of a Differential Spectrum with a Single-Channel Analyzer (SCA) The Relationship Between Pulse-Height Distribution and Energy Spectrum Energy Resolution of a Detection System The Effect of Statistical Fluctuations: The Fano Factor The Effect of Electronic Noise on Energy Resolution The Effect of Incomplete Charge Collection The Total Width Г Determination of the Energy Resolution The Response Function The Importance of Good Energy Resolution Brief Description of a Multichannel Analyzer (MCA) Calibration of a Multichannel Analyzer 310 Problems 314 References ELECTRONICS Introduction Resistance, Capacitance, Inductance, and Impedance A Differentiating Circuit An Integrating Circuit Delay Lines Pulse Shaping Timing The Leading-Edge Timing Method The Zero-Crossing Timing Method The Constant-Fraction Timing Method Coincidence-Anticoincidence Measurements Pulse-Shape Discrimination Preamplifiers Amplifiers Analog-to-Digital Converters (ADC) Multiparameter Analyzers 347 Problems 349 Bibliography 350 References 350

8 CONTENTS xiü 11 DATA ANALYSIS METHODS Introduction Curve Fitting Interpolation Schemes Least-Squares Fitting Least-Squares Fit of a Straight Line Least-Squares Fit of General Functions Folding and Unfolding Examples of Folding The General Method of Unfolding An Iteration Method of Unfolding Least-Squares Unfolding Data Smoothing 373 Problems 377 Bibliography 378 References PHOTON (GAMMA-RAY AND X-RAY) SPECTROSCOPY Introduction Modes of Energy Deposition in the Detector Energy Deposition by Photons with E < MeV Energy Deposition by Photons with E > MeV Efficiency of X-Ray and Gamma-Ray Detectors: Definitions Detection of Photons with Nal(Tl) Scintillation Counters Efficiency of Nal(Tl) Detectors Analysis of Scintillation Detector Energy Spectra Detection of Gammas with an NE 213 Organic Scintillator Detection of X-Rays with a Proportional Counter Detection of Gammas with Ge Detectors Efficiency of Ge Detectors Energy Resolution of Ge Detectors Analysis of Ge Detector Energy Spectra Timing Characteristics of the Pulse CdTe and Hgl 2 Detectors as Gamma Spectrometers Detection of X-Rays with a Si(Li) Detector Detection of X-Rays with a Crystal Spectrometer Types of Crystal Spectrometers Energy Resolution of Crystal Spectrometers 428 Problems 430 Bibliography 431 References CHARGED-PARTICLE SPECTROSCOPY Introduction 13.2 Energy Straggling

9 xiv CONTENTS 13.3 Electron Spectroscopy Electron Backscattering Energy Resolution and Response Function of Electron Detectors Energy Calibration of Electron Spectrometers Electron Source Preparation Alpha, Proton, Deuteron, and Triton Spectroscopy Energy Resolution and Response Function of Alpha Detectors Energy Calibration Source Preparation Heavy-Ion (Z > 2) Spectroscopy The Pulse-Height Defect Energy Calibration: The Schmitt Method Calibration Sources Fission Foil Preparation The Time-of-Flight Spectrometer Detector Telescopes {EdE/dx Detectors) Magnetic Spectrometers Electrostatic Spectrometers Position-Sensitive Detectors Position-Sensitive Semiconductor Detectors Multiwire Proportional Chambers 461 Problems 462 Bibliography 463 References NEUTRON DETECTION AND SPECTROSCOPY Introduction Neutron Detection by (n, Charged Particle) Reaction The BF 3 Counter Boron-Lined Counters Li Counters He Counters Fission Chambers Neutron Detection by Foil Activation Basic Equations Determination of the Neutron Flux by Counting the Foil Activity Measurement of a Neutron Energy Spectrum by Proton Recoil Differentiation Unfolding of Proton Recoil Spectra The FERDOR Unfolding Method Proportional Counters Used as Fast-Neutron Spectrometers Organic Scintillators Used as Fast-Neutron Spectrometers Detection of Fast Neutrons Using Threshold Activation Reactions The Code SAND-II The Code SPECTRA The Relative Deviation Minimization Method (RDMM) The LSL-M2 Unfolding Code Neutron Energy Measurement with a Crystal Spectrometer 503

10 CONTENTS XV 14.8 The Time-of-Flight Method The Neutron Velocity Selector (Neutron Chopper) Pulsed-Ion Beams Compensated Ion Chambers Self-Powered Neutron Detectors (SPND) SPNDs with Delayed Response SPNDs with Prompt Response Concluding Remarks 518 Problems 519 Bibliography 520 References ACTIVATION ANALYSIS Introduction Selection of the Optimum Nuclear Reaction Preparation of the Sample for Irradiation Sources of Radiation Sources of Neutrons Sources of Charged Particles Sources of Photons Irradiation of the Sample Counting of the Sample Analysis of the Results Sensitivity of Activation Analysis Interference Reactions Advantages and Disadvantages of the Activation Analysis Method 537 Problems 537 Bibliography 538 References HEALTH PHYSICS FUNDAMENTALS Introduction Units of Exposure and Absorbed Dose The Relative Biological Effectiveness The Dose Equivalent Dosimetry for Radiation External to the Body Dose Due to Charged Particles Dose Due to Photons Dose Due to Neutrons Dosimetry for Radiation Inside the Body Dose from a Source of Charged Particles Inside the Body Dose from a Photon Source Inside the Body Internal Dose Time Dependence Biological Half-Life Biological Effects of Radiation Basic Description of the Human Cell Stochastic and Nonstochastic Effects 564

11 xvi CONTENTS 16.8 Radiation Protection Guides and Exposure Limits Health Physics Instruments Survey Instruments Thermoluminescent Dosimeters Solid-State Track Recorders (SSTRs) The Bonner Sphere (the Rem Ball) The Neutron Bubble Detector The Electronic Personal Dosimeter Foil Activation Used for Neutron Dosimetry Proper Use of Radiation 582 Problems 585 Bibliography 587 References 587 APPENDIXES 589 A Useful Constants and Conversion Factors 589 В Atomic Masses and Other Properties of Isotopes 591 С Alpha, Beta, and Gamma Sources Commonly Used 595 D Tables of Photon Attenuation Coefficients 599 E Table of Buildup Factor Constants 605 INDEX 607