Tsoulfanidis N. Measurement and detection of radiation
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CONTENTS
Ionization Chambers
5.4.1
Pulse Formation in an Ionization Chamber
5.4.2
Current Ionization Chambers
Proportional Counters
5.5.1
Gas Multiplication in Proportional Counters
5.5.2
The Pulse Shape of a Proportional Counter
5.5.3
The Change of Counting Rate with High Voltage-The
High-Voltage Plateau
Geiger-Miiller Counters
5.6.1
Operation of a GM Counter and Quenching of the Discharge
5.6.2
The Pulse Shape and the Dead Time of a GM Counter
Gas-Flow Counters
5.7.1
The Long-Range Alpha Detector (LRAD)
5.7.2
Internal Gas Counting
Rate Meters
General Comments about Construction of Gas-Filled Detectors
Problems
Bibliography
References
SCINTILLATION DETECTORS
Introduction
Inorganic (Crystal) Scintillators
6.2.1
The Mechanism of the Scintillation Process
6.2.2
Time Dependence of Photon Emission
6.2.3
Important Properties of Certain Inorganic Scintillators
Organic Scintillators
6.3.1
The Mechanism of the Scintillation Process
6.3.2
Organic Crystal Scintillators
6.3.3
Organic Liquid Scintillators
6.3.4
Plastic Scintillators
Gaseous Scintillators
The Relationship Between Pulse Height and Energy and
Type of Incident Particle
6.5.1
The Response of Inorganic Scintillators
6.5.2
The Response of Organic Scintillators
The Photomultiplier Tube
6.6.1
General Description
6.6.2
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
Problems
Bibliography
References
CONTENTS
xi
SEMICONDUCTOR DETECTORS
Introduction
Electrical Classification of Solids
7.2.1
Electronic States in Solids-The Fermi Distribution Function
7.2.2 Insulators
7.2.3
Conductors
Semiconductors
7.3.1 The Change of the Energy Gap with Temperature
7.3.2 Conductivity of Semiconductors
7.3.3 Extrinsic and Intrinsic Semiconductors-The Role of Impurities
The p-n Junction
7.4.1 The Formation of a p-n Junction
7.4.2 The p-n Junction Operating as a Detector
The Different Types of Semiconductor Detectors
7.5.1 Surface-Barrier Detectors
7.5.2 Diffused-Junction Detectors
7.5.3 Silicon Lithium-Drifted [Si(Li)] Detectors
7.5.4 Germanium Lithium-Drifted [Ge(Li)] Detectors
7.5.5 Germanium (Ge) Detectors
7.5.6 CdTe and HgI, Detectors
Radiation Damage to Semiconductor Detectors
Problems
Bibliography
References
RELATIVE AND ABSOLUTE MEASUREMENTS
Introduction
Geometry Effects
8.2.1 The Effect of the Medium between Source and Detector
8.2.2 The Solid Angle-General Definition
8.2.3 The Solid Angle for a Point Isotropic Source and a
Detector with a Circular Aperture
8.2.4 The Solid Angle for a Disk Source Parallel to a Detector
with
a
Circular Aperture
8.2.5 The Solid Angle for
a
Point Isotropic Source and a Detector
with a Rectangular Aperture
8.2.6 The Solid Angle for a Disk Source and a Detector
with
a
Rectangular Aperture
8.2.7 The Use of the Monte Carlo Method for the Calculation
of the Solid Angle
Source Effects
8.3.1 Source Self-Absorption Factor
(fa)
8.3.2 Source Backscattering Factor
(f,)
Detector Effects
8.4.1
Scattering and Absorption Due to the Window of the Detector
8.4.2 Detector Efficiency
(E)
xii
CONTENTS
8.4.3 Determination of Detector Efficiency
Relationship Between Counting Rate and Source Strength
Problems
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
9.6.1 The Effect of Statistical Fluctuations: The Fano Factor
9.6.2 The Effect of Electronic Noise on Energy Resolution
9.6.3 The Effect of Incomplete Charge Collection
9.6.4 The Total Width
T
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
Problems
References
ELECTRONICS
Introduction
Resistance, Capacitance, Inductance, and Impedance
A Differentiating Circuit
An
Integrating Circuit
Delay Lines
Pulse Shaping
Timing
10.7.1
The Leading-Edge Timing Method
10.7.2 The Zero-Crossing Timing Method
10.7.3 The Constant-Fraction Timing Method
Coincidence-Anticoincidence Measurements
Pulse-Shape Discrimination
Preamplifiers
Amplifiers
Analog-to-Digital Converters
(ADC)
Multiparameter Analyzers
Problems
Bibliography
References
CONTENTS
~iii
11
DATA ANALYSIS METHODS
11.1 Introduction
11.2 Curve Fitting
11.3 Interpolation Schemes
11.4 Least-Squares Fitting
11.4.1 Least-Squares Fit of a Straight Line
11.4.2 Least-Squares Fit of General Functions
11.5 Folding and Unfolding
11.5.1 Examples of Folding
11.5.2 The General Method of Unfolding
11.5.3
An
Iteration Method of Unfolding
11
S.4 Least-Squares Unfolding
11.6 Data Smoothing
Problems
Bibliography
References
12
PHOTON (GAMMA-RAY AND X-RAY) SPECTROSCOPY
12.1 Introduction
12.2
Modes of Energy Deposition in the Detector
12.2.1 Energy Deposition by Photons with
E
<
1.022 MeV
12.2.2 Energy Deposition by Photons with
E
>
1.022 MeV
12.3
Efficiency of X-Ray and Gamma-Ray Detectors: Definitions
12.4
Detection of Photons with
NaI(Tl) Scintillation Counters
12.4.1 Efficiency of NaI(T1) Detectors
12.4.2 Analysis of Scintillation Detector Energy Spectra
12.5
Detection of Gammas with an NE 213 Organic Scintillator
12.6 Detection of X-Rays with a Proportional Counter
12.7
Detection of Gammas with Ge Detectors
12.7.1 Efficiency of Ge Detectors
12.7.2 Energy Resolution of Ge Detectors
12.7.3 Analysis of Ge Detector Energy Spectra
12.7.4 Timing Characteristics of the Pulse
12.8
CdTe and HgI, Detectors as Gamma Spectrometers
12.9
Detection of X-Rays with a Si(Li) Detector
12.10 Detection of X-Rays with a Crystal Spectrometer
12.10.1 Types of Crystal Spectrometers
12.10.2 Energy Resolution of Crystal Spectrometers
Problems
Bibliography
References
13
CHARGED-PARTICLE SPECTROSCOPY
13.1 Introduction
13.2 Energy Straggling
xiv
CONTENTS
Electron Spectroscopy
13.3.1
Electron Backscattering
13.3.2
Energy Resolution and Response Function of Electron Detectors
13.3.3
Energy Calibration of Electron Spectrometers
13.3.4
Electron Source Preparation
Alpha, Proton, Deuteron, and Triton Spectroscopy
13.4.1
Energy Resolution and Response Function of Alpha Detectors
13.4.2
Energy Calibration
13.4.3
Source Preparation
Heavy-Ion
(Z
>
2)
Spectroscopy
13.5.1
The Pulse-Height Defect
13.5.2
Energy Calibration: The Schmitt Method
13.5.3
Calibration Sources
13.5.4
Fission Foil Preparation
The Time-of-Flight Spectrometer
Detector Telescopes
(E
dE/h
Detectors)
Magnetic Spectrometers
Electrostatic Spectrometers
Position-Sensitive Detectors
13.10.1
Position-Sensitive Semiconductor Detectors
13.10.2
Multiwire Proportional Chambers
Problems
Bibliography
References
NEUTRON DETECTION AND SPECTROSCOPY
Introduction
Neutron Detection by
(n,
Charged Particle) Reaction
14.2.1
The BF, Counter
14.2.2
Boron-Lined Counters
14.2.3
6~i Counters
14.2.4
3~e Counters
Fission Chambers
Neutron Detection by Foil Activation
14.4.1
Basic Equations
14.4.2
Determination of the Neutron Flux by Counting the Foil Activity
Measurement of a Neutron Energy Spectrum by Proton Recoil
14.5.1
Differentiation Unfolding of Proton Recoil Spectra
14.5.2
The FERDOR Unfolding Method
14.5.3
Proportional Counters Used as Fast-Neutron Spectrometers
14.5.4
Organic Scintillators Used as Fast-Neutron Spectrometers
Detection of Fast Neutrons Using Threshold Activation Reactions
14.6.1
The Code SAND-I1
14.6.2
The Code SPECTRA
14.6.3
The Relative Deviation Minimization Method (RDMM)
14.6.4
The
LSL-M2
Unfolding Code
Neutron Energy Measurement with a Crystal Spectrometer
CONTENTS
xv
14.8 The Time-of-Flight Method
14.8.1 The Neutron Velocity Selector (Neutron Chopper)
14.8.2 Pulsed-Ion Beams
14.9 Compensated Ion Chambers
14.10 Self-Powered Neutron Detectors (SPND)
14.10.1 SPNDs with Delayed Response
14.10.2 SPNDs with Prompt Response
14.1
1
Concluding Remarks
Problems
Bibliography
References
15
ACTIVATION ANALYSIS
15.1 Introduction
15.2
Selection of the Optimum Nuclear Reaction
15.3
Preparation of the Sample for Irradiation
15.4 Sources of Radiation
15.4.1 Sources of Neutrons
15.4.2 Sources of Charged Particles
15.4.3 Sources of Photons
15.5 Irradiation of the Sample
15.6 Counting of the Sample
15.7 Analysis of the Results
15.8 Sensitivity of Activation Analysis
15.9 Interference Reactions
15.10 Advantages and Disadvantages of the Activation Analysis Method
Problems
Bibliography
References
16 HEALTH PHYSICS FUNDAMENTALS
16.1 Introduction
16.2
Units of Exposure and Absorbed Dose
16.3
The Relative Biological Effectiveness-The Dose Equivalent
16.4
Dosimetry for Radiation External to the Body
16.4.1 Dose Due to Charged Particles
16.4.2 Dose Due to Photons
16.4.3 Dose Due to Neutrons
16.5
Dosimetry for Radiation Inside the Body
16.5.1
Dose from a Source of Charged Particles Inside the Body
16.5.2 Dose from a Photon Source Inside the Body
16.6
Internal Dose Time Dependence-Biological Half-Life
16.7 Biological Effects of Radiation
16.7.1
Basic Description of the Human Cell
16.7.2 Stochastic and Nonstochastic Effects
xvi
CONTENTS
16.8
Radiation Protection Guides and Exposure Limits
16.9 Health Physics Instruments
16.9.1 Survey Instruments
16.9.2 Thermoluminescent Dosimeters
16.9.3 Solid-state Track Recorders
(SSTRs)
16.9.4 The Bonner Sphere (the Rem Ball)
16.9.5 The Neutron Bubble Detector
16.9.6 The Electronic Personal Dosimeter
16.9.7 Foil Activation Used for Neutron Dosimetry
16.10 Proper Use of Radiation
Problems
Bibliography
References
APPENDIXES
A
Useful Constants and Conversion Factors
B
Atomic Masses and Other Properties of Isotopes
C
Alpha,
Beta, and Gamma Sources Commonly Used
D
Tables of Photon Attenuation Coefficients
E Table of Buildup Factor Constants
INDEX
PREFACE TO THE FIRST EDITION
The material in this book, which is the result of a 10-year experience obtained in
teaching courses related to radiation measurements at the University of Mis-
souri-Rolla, is intended to provide an introductory text on the subject. It
includes not only what
I
believe the beginner ought to be taught but also some
of the background material that people involved in radiation measurements
should have. The subject matter is addressed to upper-level undergraduates and
first-year graduate students. It is assumed that the students have had courses in
calculus and differential equations and in basic atomic and nuclear physics. The
book should be useful to students in nuclear, mechanical, and electrical engi-
neering, physics, chemistry (for
radiochemistry), nuclear medicine, and health
physics; to engineers and scientists in laboratories using radiation sources; and
to personnel in nuclear power plants.
The structure and the contents of the book are such that the person who
masters the material will be able to
1
Select the proper detector given the energy and type of particle to be counted
and the purpose of the measurement.
2
Analyze the results of counting experiments, i.e., calculate errors, smooth
results, unfold energy spectra, fit results with a function, etc.
3
Perform radiation measurements following proper health physics procedures.
The first chapter defines the energy range of the different types of radiation
for which instruments and methods of measurement are considered; it gives a
brief discussion of errors that emphasizes their importance; and, finally, it
presents a very general description of the components of a counting system. This
last part of the chapter is necessary because a course on radiation measure-
ments involves laboratory work, and for this reason the students should be
familiar from the very beginning with the general features and functions of
radiation instruments.
xvii
xviii
PREFACE
TO
THE
FIRST
EDITION
The second chapter addresses the very important subject of errors. Since all
experimental results have errors, and results reported without their correspond-
ing errors are meaningless, this chapter is fundamental for a book such as this
one. Further discussion of errors caused by the analysis of the results is
presented in Chap.
11.
Chapters
3
and 4 constitute a quick review of material that should have
been covered in previous courses. My experience has been that students need
this review of atomic and nuclear physics and of penetration of radiation
through matter. These two chapters can be omitted if the instructor feels that
the students know the subject.
Chapters 5-7 describe the different types of radiation detectors. Full
chapters have been devoted to gas-filled counters, scintillation detectors, and
semiconductor detectors. Detectors with "special" functions are discussed in
Chap. 17.
The subject of relative and absolute measurements is presented in Chap.
8.
The solid angle (geometry factor) between source and detector and effects due
to the source and the detector, such as efficiency, backscattering, and source
self-absorption are all discussed in detail.
Chapter
9
is an introduction to spectroscopy. It introduces and defines the
concepts used in the next four chapters. Chapter 10 discusses the features of the
electronic components of a counting system that are important in spectroscopy.
Its objective is not to make the reader an expert in electronics but to show how
the characteristics of the instruments may influence the measurements.
Chapter
11
presents methods of analysis of experimental data. Methods of
curve fitting, of interpolation, and of least-squares fitting are discussed concisely
but clearly.
A
general discussion of folding, unfolding, and data smoothing,
which are necessary tools in analysis of spectroscopic measurements, occupies
the second half of this chapter. Special methods of unfolding for photons,
charged particles, and neutrons are further discussed in Chaps. 12 through 14,
which also cover spectroscopy. Individual chapters are devoted to photons,
charged particles, and neutrons. All the factors that affect spectroscopic mea-
surements and the methods of analysis of the results are discussed in detail.
Chapter 15 is devoted to activation analysis, a field with wide-ranging
applications. Health physics is discussed in Chap. 16.
I
feel that every person
who handles radiation should know at least something about the effects of
radiation, radiation units, and regulations related to radiation protection. This
chapter may be omitted if the reader has already studied the subject.
Chapter 17 deals with special detectors and spectrometers that have found
applications in many different fields but do not fit in any of the previous
chapters. Examples are the self-powered detectors, which may be gamma or
neutron detectors, fission track detectors, thermoluminescent dosimeters, photo-
graphic emulsions, and others.
The problems at the end of each chapter should help the student under-
stand the concepts presented in the text. They are arranged not according to
PREFACE TO
THE
FIRST EDITION
xix
difficulty but in the order of presentation of the material needed for their
solution.
The appendixes at the end of the book provide useful information to the
reader.
I use the SI (metric) units with the exception of some well-established
nonmetric units, which, it seems, are here to stay. Examples are MeV,
keV, and
eV for energy; the barn for cross sections; the curie; and the rem. These units
are given in parentheses along with their SI counterparts.
Writing a book is a tremendous undertaking, a task too big for any single
person.
I
was fortunate to have been helped by many individuals, and it gives me
great pleasure to recognize them here. First and foremost,
I
thank all the former
students who struggled through my typed notes when they took the radiation
measurements course at the University of Missouri-Rolla. Their numerous
critical comments are deeply appreciated.
I
thank my colleagues, Dr. D. Ray
Edwards for his continuous support, Dr.
G.
E.
Mueller for his many useful
suggestions, and Drs.
A.
E. Bolon and
T.
J.
Dolan for many helpful discussions
over the last
10
years. I also thank Dr. R.
H.
Johnson of Purdue University for
reviewing certain chapters.
I
especially thank my dear friend Professor
B.
W.
Wehring of the University of Illinois for numerous lengthy discussions following
his detailed critical review of most of the chapters.
I
am grateful to Mrs. Susan
Elizagary for expertly typing most of the manuscript and to Mrs. Betty Volosin
for helping in the final stages of typing.
No single word or expression of appreciation can adequately reflect my
gratitude to my wife Zizeta for her moral support and understanding during the
last three painstaking years, and to my children Steve and Lena for providing
pleasant and comforting distraction.
Nicholas Tsoulfanidis