iaea international atomic energy agency basic nuclear physics - 3 modes of radioactive decay and...
TRANSCRIPT
![Page 1: IAEA International Atomic Energy Agency Basic Nuclear Physics - 3 Modes of Radioactive Decay and Types of Radiation Day 1 – Lecture 3](https://reader030.vdocuments.net/reader030/viewer/2022032708/56649e5d5503460f94b5540c/html5/thumbnails/1.jpg)
IAEAInternational Atomic Energy Agency
Basic Nuclear Physics - 3
Modes of Radioactive Decay and Types of Radiation
Day 1 – Lecture 3
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IAEA 2
Objective
To understands modes of radioactive disintegration and types of radiation
To learn about basic atomic structure;
alpha, beta, and gamma decay; positron emission; differences between gamma rays and x-rays; orbital electron capture; and internal conversion
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IAEA 3
Content
Basic atomic structure and isotopes
Alpha, beta, and gamma decay
Decay spectra
Differences between gamma rays and x-rays
Positron emission
Orbital electron capture
Internal conversion
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IAEA 4
proton neutron electron
Atomic Structure
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IAEA 5
Atomic Number (Z)
Hydrogen 1
Carbon 6
Cobalt 27
Selenium 34
Iridium 77
Uranium 92
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IAEA
Isotopes
An isotope of an element has:
the same number of protons
a different number of neutrons
1H 2H 3H
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IAEA
Isotopes
The number of protons determines the element. Elements with the same number of protons but different numbers of neutrons are called isotopes. Some isotopes are radioactive.
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IAEA 8
Radioactive Decay
Spontaneous changes in the nucleus of an unstable atom
Results in formation of new elements
Accompanied by a release of energy, either particulate or electromagnetic or both
Nuclear instability is related to whether the neutron to proton ratio is too high or too low
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IAEA 9
The Line of Stability
N > Z
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IAEA 10
Alpha Emission
Emission of a highly energetic helium nucleus from the nucleus of a radioactive atom
Occurs when neutron to proton ratio is too low
Results in a decay product whose atomic number is 2 less than the parent and whose atomic mass is 4 less than the parent
Alpha particles are monoenergetic
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IAEA 11
Alpha particle
charge +2
Alpha Particle Decay
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IAEA 12
Alpha Particle Decay
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IAEA 13
Alpha Decay Example
226Ra decays by alpha emission
When 226Ra decays, the atomic mass decreases by 4 and the atomic number decreases by 2
The atomic number defines the element, so the element changes from radium to radon
226Ra 222Rn + 4He28688
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IAEA 14
Beta Emission
Emission of an electron from the nucleus of a radioactive atom ( n p+ + e-1 )
Occurs when neutron to proton ratio is too high (i.e., a surplus of neutrons)
Beta particles are emitted with a whole spectrum of energies (unlike alpha particles)
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IAEA 15
Beta particlecharge -1
Beta Particle Decay
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IAEA 16
Beta Particle Decay
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IAEA 17
Beta Decay of 99Mo
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IAEA 18
Beta Spectrum
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IAEA 19
Rule of Thumb
Average energy of a beta spectrum is about one-third of its maximum energy or:
Eav = Emax13
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IAEA 20
Positron (Beta+) Emission
Occurs when neutron to proton ratio is too low ( p+ n + e+ )
Emits a positron (beta particle whose charge is positive)
Results in emission of 2 gamma rays (more on this later)
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IAEA 21
Positron (Beta+) Emission
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IAEA 22
Positron Decay
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IAEA 23
Positron Decay
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IAEA 24
Positron Decay
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IAEA 25
Positron Annihilation
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IAEA 26
Orbital Electron Capture
Also called K Capture
Occurs when neutron to proton ratio is too low
Form of decay competing with positron emission
One of the orbital electrons is captured by the nucleus: e-1 + p+1 n
Results in emission of characteristic x-rays
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IAEA 27
Orbital Electron Capture
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IAEA 28
Orbital Electron Capture
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IAEA 29
radiationpath
-1
ejectedelectron+1
ionizedatom
Ionization
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IAEA 30
characteristicx-rays
X-Ray Production
electronejected
electron fillsvacancy
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IAEA 31
Electromagnetic Spectrum
x- and -raysInfra-red
Ultra-violet Visible
Increase in wavelength : decrease in frequency and energy
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IAEA 32
Gamma Ray Emission
Monoenergetic radiations emitted from nucleus of an excited atom following radioactive decay
Rid nucleus of excess energy
Have characteristic energies which can be used to identify the radionuclide
Excited forms of radionuclides often referred to as “metastable”, e.g., 99mTc. Also called “isomers”
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IAEA 33
Gamma Radiation
Gamma Ray Emission
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IAEA 34
Gamma Ray Emission
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IAEA 35
Photon Emission
DifferenceBetween
X-Rays andGamma Rays
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IAEA 36
Internal Conversion
Alternative process by which excited nucleus of a gamma emitting isotope rids itself of excitation energy
The nucleus emits a gamma ray which interacts with an orbital electron, ejecting the electron from the atom
Characteristic x-rays are emitted as outer orbital electrons fill the vacancies left by the conversion electrons
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IAEA 37
Internal Conversion
These characteristic x-rays can themselves be absorbed by orbital electrons, ejecting them.
These ejected electrons are called Auger electrons and have very little kinetic energy
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IAEA 38
Internal Conversion
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IAEA 39
Summary of Radioactive Decay Mechanisms
DecayMode
Characteristicsof Parent
Radionuclide
Change in Atomic Number
(Z)
Change inAtomic Mass Comments
Alpha Neutron Poor -2 -4 Alphas Monoenergetic
Beta Neutron Rich +1 0 Beta Energy Spectrum
Positron Neutron Poor -1 0 Positron Energy Spectrum
ElectronCapture
Neutron Poor -1 0K-Capture; Characteristic
X-rays Emitted
GammaExcited
Energy StateNone None Gammas Monoenergetic
Internal Conversion
Excited Energy State
None NoneEjects Orbital Electrons; characteristic x-rays and Auger electrons emitted
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IAEA 40
Summary
Basic atomic structure was described Isotopes were defined Modes of radioactive disintegration were
discussed (including alpha, beta, gamma, positron emission, orbital electron capture, and internal conversion)
Ionization was defined X-ray production and the differences
between gamma rays and x-rays were described
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IAEA 41
Where to Get More Information
Cember, H., Johnson, T. E, Introduction to Health Physics, 4th Edition, McGraw-Hill, New York (2009)
International Atomic Energy Agency, Postgraduate Educational Course in Radiation Protection and the Safety of Radiation Sources (PGEC), Training Course Series 18, IAEA, Vienna (2002)