3/2003 Rev 1 I.2.6 – slide 1 of 43 Session I.2.6 Part I Review of Fundamentals Module 2Basic...
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Transcript of 3/2003 Rev 1 I.2.6 – slide 1 of 43 Session I.2.6 Part I Review of Fundamentals Module 2Basic...
3/2003 Rev 13/2003 Rev 1 I.2.6 – slide I.2.6 – slide 11 of 43 of 43
Session I.2.6Session I.2.6
Part I Review of Fundamentals
Module 2Basic Physics and MathematicsUsed in Radiation Protection
Session 6Modes of Radioactive Modes of Radioactive Decay and Types of Radiation Decay and Types of Radiation
IAEA Post Graduate Educational CourseIAEA Post Graduate Educational CourseRadiation Protection and Safe Use of Radiation SourcesRadiation Protection and Safe Use of Radiation Sources
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IntroductionIntroduction
Modes of radioactive decay and types of Modes of radioactive decay and types of radiation emitted will be discussedradiation emitted will be discussed
Students will learn about basic atomic Students will learn about basic atomic structure; alpha, beta, and gamma decay; structure; alpha, beta, and gamma decay; positron emission; differences between positron emission; differences between gamma rays and x-rays; orbital electron gamma rays and x-rays; orbital electron capture; and internal conversioncapture; and internal conversion
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ContentContent
Basic atomic structure and isotopesBasic atomic structure and isotopes
Alpha, beta, and gamma decayAlpha, beta, and gamma decay
Decay spectraDecay spectra
Differences between gamma rays and x-raysDifferences between gamma rays and x-rays
Positron emissionPositron emission
Orbital electron captureOrbital electron capture
Internal conversionInternal conversion
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OverviewOverview
Fundamental atomic structure will be Fundamental atomic structure will be describeddescribed
Modes of radioactive disintegration Modes of radioactive disintegration and types of radiation emitted will be and types of radiation emitted will be discusseddiscussed
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proton neutron electron
Atomic StructureAtomic Structure
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Atomic Number (Z)Atomic Number (Z)
HydrogenHydrogen 11
CarbonCarbon 66
CobaltCobalt 2727
SeleniumSelenium 3434
IridiumIridium 7777
UraniumUranium 9292
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IsotopesIsotopes
An isotope of an element has:An isotope of an element has:
the same number of the same number of protonsprotons
a different number of a different number of neutronsneutrons
1H 2H 3H
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IsotopesIsotopes
The number of The number of protons determines protons determines the element. the element. Elements with the Elements with the same number of same number of protons but different protons but different numbers of neutrons numbers of neutrons are called isotopes. are called isotopes. Some isotopes are Some isotopes are radioactive.radioactive.
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Radioactive DecayRadioactive Decay
Spontaneous changes in the Spontaneous changes in the nucleusnucleus of an of an unstableunstable atom atom
Results in formation of new elementsResults in formation of new elements
Accompanied by a release of energy, either Accompanied by a release of energy, either particulate or electromagnetic or bothparticulate or electromagnetic or both
Nuclear instability is related to whether the Nuclear instability is related to whether the neutron to proton ratio is too high or too lowneutron to proton ratio is too high or too low
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The Line of StabilityThe Line of Stability
N > Z
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Alpha EmissionAlpha Emission
Emission of a highly energetic helium nucleus Emission of a highly energetic helium nucleus from the nucleus of a radioactive atomfrom the nucleus of a radioactive atom
Occurs when neutron to proton ratio is too Occurs when neutron to proton ratio is too lowlow
Results in a decay product whose atomic Results in a decay product whose atomic number is 2 less than the parent and whose number is 2 less than the parent and whose atomic mass is 4 less than the parentatomic mass is 4 less than the parent
Alpha particles are monoenergeticAlpha particles are monoenergetic
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Alpha particleAlpha particle
charge +2charge +2
Alpha Particle DecayAlpha Particle Decay
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Alpha Particle DecayAlpha Particle Decay
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Alpha Decay ExampleAlpha Decay Example
226226Ra decays by alpha emissionRa decays by alpha emission
When When 226226Ra decays, the atomic mass decreases Ra decays, the atomic mass decreases by 4 and the atomic number decreases by 2by 4 and the atomic number decreases by 2
The atomic number defines the element, so the The atomic number defines the element, so the element changes from radium to radonelement changes from radium to radon
226226Ra Ra 222222Rn + Rn + 44HeHe2286868888
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Beta EmissionBeta Emission
Emission of an electron from the nucleus Emission of an electron from the nucleus of a radioactive atom ( n of a radioactive atom ( n p p++ + e + e-1-1 ) )
Occurs when neutron to proton ratio is too Occurs when neutron to proton ratio is too high (i.e., a surplus of neutrons)high (i.e., a surplus of neutrons)
Beta particles are emitted with a whole Beta particles are emitted with a whole spectrum of energies (unlike alpha spectrum of energies (unlike alpha particles)particles)
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Beta particleBeta particlecharge -1charge -1
Beta Particle DecayBeta Particle Decay
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Beta Particle DecayBeta Particle Decay
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Beta Decay of Beta Decay of 9999MoMo
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Beta SpectrumBeta Spectrum
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Rule of ThumbRule of Thumb
Average energy of a beta spectrum is about Average energy of a beta spectrum is about one-third of its maximum energy or:one-third of its maximum energy or:
EEavav = E = Emaxmax1133
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Positron (BetaPositron (Beta++) Emission) Emission
Occurs when neutron to proton ratio is Occurs when neutron to proton ratio is too low ( ptoo low ( p++ n + e n + e++ ) )
Emits a positron (beta particle whose Emits a positron (beta particle whose charge is positive)charge is positive)
Results in emission of 2 gamma rays Results in emission of 2 gamma rays (more on this later)(more on this later)
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Positron (BetaPositron (Beta++) Emission) Emission
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Positron DecayPositron Decay
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Positron DecayPositron Decay
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Positron DecayPositron Decay
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Positron AnnihilationPositron Annihilation
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Orbital Electron CaptureOrbital Electron Capture
Also called K CaptureAlso called K Capture
Occurs when neutron to proton ratio is too Occurs when neutron to proton ratio is too lowlow
Form of decay competing with positron Form of decay competing with positron emissionemission
One of the orbital electrons is captured by One of the orbital electrons is captured by the nucleus: ethe nucleus: e-1-1 + p + p+1+1 n n
Results in emission of characteristic x-raysResults in emission of characteristic x-rays
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Orbital Electron CaptureOrbital Electron Capture
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Orbital Electron CaptureOrbital Electron Capture
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radiationpath
-1
ejectedelectron+1
ionizedatom
IonizationIonization
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characteristicx-rays
X-Ray ProductionX-Ray Production
electronelectronejectedejected
electron fillselectron fillsvacancyvacancy
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Electromagnetic SpectrumElectromagnetic Spectrum
x- and x- and -rays-raysInfra-Infra-redred
Ultra-Ultra-violetviolet VisibleVisible
Increase in wavelength : decrease in frequency and energyIncrease in wavelength : decrease in frequency and energy
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Gamma Ray EmissionGamma Ray Emission
Monoenergetic radiations emitted from Monoenergetic radiations emitted from nucleus of an excited atom following nucleus of an excited atom following radioactive decayradioactive decay
Rid nucleus of excess energyRid nucleus of excess energy
Have characteristic energies which can be Have characteristic energies which can be used to identify the radionuclideused to identify the radionuclide
Excited forms of radionuclides often Excited forms of radionuclides often referred to as “metastable”, e.g., referred to as “metastable”, e.g., 99m99mTc. Tc. Also called “isomers”Also called “isomers”
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Gamma Radiation
Gamma Ray EmissionGamma Ray Emission
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Gamma Ray EmissionGamma Ray Emission
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Photon EmissionPhoton Emission
DifferenceDifferenceBetween Between
X-Rays andX-Rays andGamma RaysGamma Rays
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Internal ConversionInternal Conversion
Alternative process by which excited Alternative process by which excited nucleus of a gamma emitting isotope rids nucleus of a gamma emitting isotope rids itself of excitation energyitself of excitation energy
The nucleus emits a gamma ray which The nucleus emits a gamma ray which interacts with an orbital electron, ejecting interacts with an orbital electron, ejecting the electron from the atomthe electron from the atom
Characteristic x-rays are emitted as outer Characteristic x-rays are emitted as outer orbital electrons fill the vacancies left by the orbital electrons fill the vacancies left by the conversion electronsconversion electrons
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Internal ConversionInternal Conversion
These characteristic x-rays can themselves These characteristic x-rays can themselves be absorbed by orbital electrons, ejecting be absorbed by orbital electrons, ejecting them.them.
These ejected electrons are called These ejected electrons are called AugerAuger electronselectrons and have very little kinetic energy and have very little kinetic energy
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Internal ConversionInternal Conversion
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Internal Internal Conversion Conversion
Electron Electron emitted emitted
about 10%about 10%
Internal ConversionInternal Conversion
137Cs Emits Betas
0.946 x 0.898 = 0.85
Gamma Gamma Ray emitted Ray emitted during 85% during 85%
of of 137137Cs Cs transitionstransitions
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Summary of Radioactive Decay MechanismsSummary of Radioactive Decay Mechanisms
DecayDecay
ModeMode
CharacteristicsCharacteristics
of Parent of Parent RadionuclideRadionuclide
Change in Change in
Atomic NumberAtomic Number
(Z)(Z)
Change inChange in
Atomic Atomic MassMass CommentsComments
AlphaAlpha Neutron PoorNeutron Poor -2-2 -4-4 Alphas MonoenergeticAlphas Monoenergetic
BetaBeta Neutron RichNeutron Rich +1+1 00 Beta Energy SpectrumBeta Energy Spectrum
PositronPositron Neutron PoorNeutron Poor -1-1 00 Positron Energy SpectrumPositron Energy Spectrum
ElectronElectron
CaptureCaptureNeutron PoorNeutron Poor -1-1 00
K-Capture; Characteristic K-Capture; Characteristic X-rays EmittedX-rays Emitted
GammaGammaExcited Excited
Energy StateEnergy StateNoneNone NoneNone Gammas MonoenergeticGammas Monoenergetic
Internal Internal ConversionConversion
Excited Excited
Energy StateEnergy StateNoneNone NoneNone
Ejects Orbital Electrons; Ejects Orbital Electrons; characteristic x-rays and characteristic x-rays and Auger electrons emittedAuger electrons emitted
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SummarySummary
Basic atomic structure was describedBasic atomic structure was described Isotopes were definedIsotopes were defined Modes of radioactive disintegration were Modes of radioactive disintegration were
discussed (including alpha, beta, gamma, discussed (including alpha, beta, gamma, positron emission, orbital electron capture, positron emission, orbital electron capture, and internal conversion)and internal conversion)
Ionization was definedIonization was defined X-ray production and the differences X-ray production and the differences
between gamma rays and x-rays were between gamma rays and x-rays were describeddescribed
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Where to Get More InformationWhere to Get More Information
Cember, H., Introduction to Health Physics, 3Cember, H., Introduction to Health Physics, 3rdrd Edition, McGraw-Hill, New York (2000)Edition, McGraw-Hill, New York (2000)
Firestone, R.B., Baglin, C.M., Frank-Chu, S.Y., Eds., Firestone, R.B., Baglin, C.M., Frank-Chu, S.Y., Eds., Table of Isotopes (8Table of Isotopes (8thth Edition, 1999 update), Wiley, Edition, 1999 update), Wiley, New York (1999)New York (1999)
International Atomic Energy Agency, The Safe Use International Atomic Energy Agency, The Safe Use of Radiation Sources, Training Course Series No. 6, of Radiation Sources, Training Course Series No. 6, IAEA, Vienna (1995)IAEA, Vienna (1995)