Table Of ContentPhysics and Engineering of Radiation Detection
Physics and Engineering
of Radiation Detection
Second Edition
Syed Naeem Ahmed
President, Clickmox Solutions Inc.
Adjunct Professor, Laurentian University
Sudbury, Ontario, Canada
AMSTERDAM BOSTON HEIDELBERG LONDON NEWYORK OXFORD
(cid:1) (cid:1) (cid:1) (cid:1) (cid:1)
PARIS SANDIEGO SANFRANCISCO SYDNEY TOKYO
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Elsevier
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Dedicated to:
my parents whose loving memories still guide me
through difficult times; my wife, Rahat, without whose utmost love,
support, and encouragements it would not have been possible to write
this book; and to my children Hiba, Shozab, and Shanib, who have
taught me things about life I could never have learned myself.
Preface to the second edition
It has been more than six years since the first edition of this book was published.
The book has been well received by academics, students and researchers and this
second edition is primarily based on the valuable suggestions on improvements
received from these readers. It provides technical corrections and clarifications in
all chapters and summarizes new developments in the field of radiation detection
andmeasurementincludinglatestdosimetrystandards.
I am highly thankful to the readers who have critiqued the book in a very
productivemannerandhaveprovidedfeedbacks.Theirsuggestionshavebeentaken
into consideration while writing this second edition. My apologies to those
academics who have long been waiting for the solution key to the end-of-chapter
problems. The key is now being made available to instructors together with some
otherteachingresources.
Working with Academic Press/Elsevier was again a pleasure. Specifically,
IwouldliketothankAnitaKoch,ShannonStanton,andPoulouseJosephinhelping
mecompletethissecondeditionontime.
SyedNaeemAhmed
Sudbury,October2014
Preface to the first edition
Contrary to common perception, radiation has enormous potential of benefiting
mankind. For example, use of radiation in medical diagnostics in the form of CT
and nuclear scans has enabled the physicians to perform diagnoses that would not
have been possible otherwise. Another example is the use of radiation to destroy
cancerous growths, a process generally known as radiation therapy. It is true that
radiation can induce harm as well but a close examination reveals that its benefits
certainly outweigh its potential hazards. This realization has led to rapid advance-
ments in theory and applications of radiation interactions and its measurements.
New types of radiation detectors and sources are being constantly developed in lab-
oratories around the world. Also, a number of annually held international confer-
encesaredevotedjusttothedevelopmentsofradiationmeasuringdevices.
During my career as a physicist, working primarily on radiation detectors,
Ialwaysfeltaneedforabookthatwouldnotonlydiscussthetechnologicalaspects
of the field but would also give a thorough account of the underlying physical prin-
ciples. The scarcity of such books led me to think about writing one myself.
However, those who understand the field would appreciate that writing such a book
isnotaneasytaskduemainlytothefastpaceddevelopmentsintherelatedtechnol-
ogies. The strategy that I therefore adopted was to concentrate on theories, method-
ologies, and technologies that are of fundamental value in terms of understanding
theconceptualbasisoftheradiationdevices.
Thesolepurposeofthebookisnottointroducethereadertotheworkingprinci-
ples of different types of radiation detectors. It has been designed and written such
that it encompasses all aspects of design, development, and effective use of the
detection devices. Therefore chapters on statistics, data analysis, software for data
analysis, dosimetry, and spectroscopy have also been included. It can be used as a
text for related courses in physics, nuclear engineering, physical chemistry, and
medical physics. It can also be used as a reference by professionals and students
workingintherelatedfields.
Most of the courses related to radiation measurements start with an introduction
to different types of radiation and their sources. I have adopted the same strategy.
The first chapter introduces the reader to various types of radiation and their
sources. It also includes sections on radioactivity and its measurements. Chapter 2
deals with the mechanisms by which radiation interacts with matter. Those who
want to understand the working principles of radiation detectors, must go through
this chapter as thoroughly as possible. The next chapter introduces the reader to the
principles of gas filled detectors, such as proportional counters. Gas filled detectors
are the earliest built radiation detectors and are still extensively used in different
xviii Prefacetothefirstedition
fields. The important concepts, such as electron-ion pair generation, recombination,
drift and diffusion of charges, avalanche creation, and breakdown have been thor-
oughly discussed with necessary mathematics. Some specific types of gas filled
detectors have also been discussed. Chapter 4 deals with liquid filled detectors.
Liquid filled detectors have recently gained considerable popularity. This chapter
gives the reader an overview of the charge production and transport processes in
liquids and how different types of liquid filled detectors are built. Solid state detec-
tors are perhaps the most widely used detectors today. Chapter 5 deals with differ-
ent types of solid state detectors, such as semiconductor detectors, diamond
detectors,andthermoluminescentdetectors.Amajorproblemwithsolidstatedetec-
tors is their vulnerability to radiation. Radiation damage mechanisms are therefore
thoroughly discussed in this chapter. Scintillation detectors and photodetectors are
thetopicsofchapter6.Thischapternotonlyintroducesthereadertothebasicscin-
tillation mechanisms but also discusses important properties of the commonly used
scintillators. For subsequent photodetection, the transfer to scintillation photons are
a major issue. The topic of light guides has therefore been given due attention.
Detection of these photons is the next step, which can be accomplished with differ-
ent types of detectors. Two such devices, that is photomultiplier tubes and
avalanche photodiode detectors have been thoroughly discussed in this chapter.
Chapter 7 deals with position sensitive detection and imaging. The basic principles
of position sensitive and imaging devices as well as related techniques have been
discussed here. The reader is also introduced to a number of position sensitive and
imagingdevices.Signalprocessingistheheartoftoday’selectronicradiationdetec-
tors.Amajorportionofthemanpowerandcapitalisthereforeinvestedindesigning
and building electronics for detection devices. This chapter exposes the reader to
the basic electronic circuitry used in radiation detectors. Different types of pream-
plifiers, shapers, filters, discriminators, and analog-to-digital converters have been
discussed here. The issues of electronics noise have also been given due attention.
Chapter 9 gives a detailed discussion of the statistics and data analysis techniques.
The topics related to probability, error propagation, correlation, regression, time
series analysis, and counting statistics have been discussed in detail. Chapter 10
gives an overview of different data analysis software packages that are freely and
commercially available. This chapter is not intended to be a manual of these soft-
ware packages. It introduce the reader to their capabilities with regard to analyzing
data that has been acquired through radiation detection devices. Dosimetry is the
topic of chapter 11. Since dosimetry plays a central role in assuring health and
safety of individuals exposed to radiation, this chapter gives a detailed account of
the subject. The harmful effects of radiation and how to guard against them have
also been discussed in this chapter. Chapter 12 introduces the reader to the topics
related to radiation spectroscopy. Different spectroscopic techniques related to dif-
ferent types of particle detectors have been introduced here. Also included are
topics of mass spectroscopy and time spectroscopy. Chapter 13 deals with the topic
of data acquisition. The major data acquisition standards of NIM, CAMAC, VME,
FASTBUS,andPCIhavebeenintroduced.
Prefacetothefirstedition xix
Writing this book has been a long and tedious process. The highly demanding
work at the Sudbury Neutrino Observatory including on-call periods did not leave
much choice other than cutting down on family time. Coming back from work and
then immediately start working on the book till midnight every day is not a very
family oriented approach. However my wife, Rahat, not only didn’t complain but
actually kept encouraging me all the way through. Without her support, it would
not have been possible at all to write this book. My children Hiba, Shozab, and
Shanibalsodeserveappreciationfortheirunderstanding.
A number of academics and friends who evaluated the original book proposal
and gave valuable suggestions deserve special thanks. I thank Andy Klein, Bashar
Issa, David Hamby, Edward Waller, John Antolak, Nicholas Hangiandreou, Niko-
laj Pavel, Paul Jennesen, Robert LeClair, Steven Biegalski, Sukesh Aghara, and
TimothyDeVolfortheirsupportandhighlyprofessionalsuggestions.
Thanks are also due to the academics who evaluated the first draft of the com-
plete manuscript. Their valuable suggestions helped me modify the contents and
reshape various sections. I am highly indebted to Andrea Kritcher, David Bradley,
James Chu, Leslie Braby, Steven Biegalski, and Todd Allen for sparing time from
their busy schedules to do thorough reviews of approximately 750 pages and pro-
vidingmewithhighlyvaluablesuggestionsforimprovement.
I would like to thank Susan Rabiner to have faith in me to complete the project
and for taking care of everything else so that I could concentrate on writing the
book. I also thank Jeremy Hayhurst for showing remarkable professionalism from
the beginning till the end of the manuscript production. Thanks are also due to
Derek Coleman, whose highly efficient and professional approach in finalizing the
manuscripthasamazedme.
1
Properties and sources of
radiation
Mass and energy are the two entities that make up our universe. At the most basic
level, these two entities represent a single reality that sometimes shows itself as
mass and sometimes as energy. They are intricately related to each other through
Einstein’s famous mass(cid:1)energy relation, E5mc2. Just like matter, energy is also
capable of moving from one point in space to another through particles or waves.
These carriers of energy always originate from some source and continue their
travel in space until they get absorbed by or annihilated in some material. The term
“radiation” is used to describe this transportation of mass and energy through
space.
Since the realization of its potential, radiation has played a central role in tech-
nologicaldevelopmentsinavarietyoffields.Forexample,weallenjoythebenefits
of radiation in medical diagnostics and treatment. On the other hand, the world has
also witnessed the hazards of radiation in the form of atomic explosions and radia-
tionexposure.
Whetherwethinkofradiationasahazardorablessing,itsstudyisofparamount
importance for our survival and development. If we look carefully at the benefits
andharmsbroughtaboutbytheuseormisuseofradiation,wewouldreachthecon-
clusion that its advantages clearly outweigh its disadvantages. Radiation has unlim-
itedpotential,anditsproperusecanbehighlybeneficialformankind.
Thischapterwillintroducethereadertodifferenttypesofradiation,theirproper-
ties, and their sources. The mechanisms through which the particles interact with
matterwillbediscussedindetailinthenextchapter.
1.1 Types of radiation
Radiation can be categorized in different ways, such as ionizing and non-ionizing,
particlesandwaves,hazardousandnon-hazardous,etc.However,noneofthesecate-
gorizations draw solid boundaries between properties of the individual particles
comprising the radiation;rather, they show the bulk behavior ofparticle beams. For
example,itwouldnotbecorrecttoassertthatanelectronalwaysionizesatomswith
which it interacts by arguing that it belongs to the category of ionizing particles.
All we can say is that if alarge number ofelectrons interact with a large number of
atoms,thepredominantmodeofinteractionwillleadtotheionizationofatoms.
PhysicsandEngineeringofRadiationDetection.DOI:http://dx.doi.org/10.1016/B978-0-12-801363-2.00001-2
©2015ElsevierInc.Allrightsreserved.
2 PhysicsandEngineeringofRadiationDetection
Sometimesradiationischaracterizedonthebasisofitswaveandparticleproper-
ties. However, as we will explore in the next section, this characterization is some-
what vague and can be a cause of confusion. The reason is that, according to
modern physics, one can associate a wavelength with every particle whether it car-
ries a mass or not. This implies that a particle having mass can act as a wave and
takepartintheformationofinterferenceanddiffractionpatterns.Ontheotherhand,
light,whichiscomprisedofphotons,isgenerallydescribedbyitswavecharacter.
Let us have a look at the third category mentioned above: hazardous and non-
hazardous. There are particles that pass through our bodies in large numbers every
second (such as neutrinos from the Sun) but do not cause any observable damage.
Still, there is a possibility that some of these particles could cause mutations in our
bodycells,whichcouldultimatelyleadtocancer.1Ontheotherhand,therearepar-
ticles, such as neutrons, that are known to be extremely hazardous to biological
organisms,butnoonecaneverbeabsolutelycertainthataparticularneutronwould
definitelycauseharm.
The above arguments point toward the idea that the characterization of particles
should be based on statistical nature of their interactions. What this really means is
that if we have a very large number of a certain kind of particle, there is a high
probability that most of them would behave in the manner characteristic of their
categorization. For example, long exposure to a highly intense beam of neutrons
would most definitely cause skin burns and most probably cancer, but it would be
wrongtoassumethatasingleneutronwoulddefinitelycausethesameeffects.
The words probability and chance were mentioned in the preceding paragraphs.
Whatdoesparticleinteractionhavetodowithchance?Well,thetheoreticalfounda-
tion of particle interaction is quantum mechanics, which quantifies the variables
related to particle motion, such as momentum, energy, and position, in probabilistic
terms. For example, in quantum mechanics we talk about the probability of a parti-
cle being present at a specific place at a certain time, but we do not claim that the
particle will definitely be there at that time. Nothing is absolute in quantum
mechanics. We will learn more about this when we study the concept of cross sec-
tioninthenextchapter.
1.2 Waves or particles?
If we think about light without any prior knowledge, we would assume it to be
composed of waves that are continuously emitted from a source (such as a light
bulb). In fact, this was the dominant perception among scientists until the start of
the twentieth century. In those days a major problem of theoretical physics had
1Thisisapurelyhypotheticalsituationandnodataexiststhatcouldverifythisassertion.Theargument
isbasedontheinteractionmechanismsofparticles.
