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Great Ideas in Science:
Lecture 7
Nuclear ReactionsProfessor Robert Hazen
UNIV 301
Great Idea: Nuclear energy arises from
the conversion of mass into energy.
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Nuclear Reactions
Key Idea: Nuclear reactions resultfrom the rearrangement of an atom
sprotons and neutrons (i.e. the nucleus)Key Words:
Proton Neutron Nucleus Isotope Radioactivity Nuclear Fission Nuclear Fusion
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The Building Blocksof Matter
Of what is matter made? Atoms Nuclei and electrons Quarks
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Key Words About Atoms
Atom: Any object with a nucleusand electronsElement: An atom with a known
number of protons (the atomicnumber)Ion: An electronically-charged
atom with a different number ofprotons (+) and electrons (-)Isotope: An element with a
known number of neutrons
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The Structure of the AtomElectrons in shells (energy levels)
Negatively chargedShift during chemical reactions
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The Structure of the AtomElectrons in shells (energy levels)
Negatively chargedShift during chemical reactions
Central dense nucleusComposed of protons and neutronsPositively chargedNucleus - Stays put in chemical reactions
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Isotopes: Hydrogen & Carbon
H-1 1 protonH-2 1 p & 1 neutron (Deuterium)H-3 1 p & 2 n (Tritium)
C-12 6p & 6nC-13 6p & 7nC-14 6p & 8n (radioactive)
For any given element the numberof protons is fixed
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Four Fates of Isotopes
An isotope may be stable
An isotope may be radioactive
An isotope may be split apartby fission
An isotope may combine withanother by fusion
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Chart of the Isotopes (Z vs. N)
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Stable Isotopes99.999+% of all the atomsaround usExamples are carbon-12 andcarbon-13Different isotopes don t affectchemical reactions.Used in scientific research totrack chemical reactions (2 ways)
As tracers Fractionation
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Radioactivity or RadioactiveDecay (three kinds)
Alpha radiation
Beta radiation
Gamma radiation
The spontaneous emission of anenergetic particle by a nucleus
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Most Kinds of Isotopesare Radioactive
STABLE
RADIOACTIVE
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Alpha RadiationAtom spontaneously loses 2 protons and
2 neutrons (= a Helium-4 nucleus)
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Alpha RadiationAtom spontaneously loses 2 protons and
2 neutrons (= a Helium-4 nucleus)Uranium-238 Thorium-234 + 2n + 2p
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Beta RadiationOne neutron spontaneously becomes
a proton plus an electronThorium-234 Proactinium-234
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Gamma RadiationAtom spontaneously emits a gamma
ray (electromagnetic radiation)Uranium-238* Uranium-238 +
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Gamma RadiationAtom spontaneously emits a gamma
ray (electromagnetic radiation)Uranium-238* Thorium 234 +
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SUMMARY: The Three Kindsof Radioactive Decay
Alpha Decay Release of particle with 2
protons and 2 neutronsBeta Decay
Neutron becomes a proton Emission of electron ( -ray)
Gamma Radiation Electromagnetic radiation
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Radioactivity and Health
Ionization Stripping offelectrons
Long-term effects Cancer Birth defects
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Half-LifeThe average time for decay of
batch of radioactive isotopesWide range of half-lives
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Radiometric Dating1. Know half-life of isotope
2. Know how much was there3. Measure what
s left
Carbon-14: Half-life = 5730 years
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Radiometric DatingApplications to geology
Need longer half-lives Uranium, potassium
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Radioactive Decay Chain (radon)
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Radioactive Decay Chain (radon)
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Radioactive Decay Chain (radon)
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Radioactive Decay Chain (radon)
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Radioactive Decay Chain (radon)
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Radioactive Decay Chain (radon)
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Radioactive Decay Chain (radon)
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Radioactive Decay Chain (radon)
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Radioactive Decay Chain (radon)
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Radioactive Decay Chain (radon)
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Radioactive Decay Chain (radon)
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Radioactive Decay Chain (radon)
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Radioactive Decay Chain (radon)
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Four Fates of Isotopes
An isotope may be stableAn isotope may be radioactive
An isotope may be split apartby fissionAn isotope may combine with
another by fusion
N l Fi i (S li i )
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Nuclear Fission (Splitting)Fission = Splittingof nucleusA nuclear reactorconverts mass toenergy
N l Fi i (S li i )
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Nuclear Fission (Splitting)
N l Fi i Th At B b
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Nuclear Fission The Atom Bomb
Hiroshima August 6, 1945
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Nuclear Fission The Atom Bomb
Yucca Mountain Nevada
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Yucca Mountain, Nevada(NIMBY)
Yucca Mountain Nevada
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Yucca Mountain, Nevada(NIMBY)
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Four Fates of Isotopes
An isotope may be stableAn isotope may be radioactive
An isotope may be split apartby fissionAn isotope may combine withanother by fusion
Nuclear Fusion (Fusing)
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Nuclear Fusion (Fusing)
Hydrogen atomscombine to form helium Some mass is converted
into energy
N l F i H d B b
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Nuclear Fusion Hydrogen Bomb
N l F i H d B b
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Nuclear Fusion Hydrogen Bomb
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Stars are Giant Fusion Reactors
http://www.earth.northwestern.edu/people/seth/107/Solar/Image12.gif
f S
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Fates of Stars
B fit f I t
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Benefits of IsotopesStable Isotopes
Medical Research Environmental Tracers
Radioactive Isotopes Medical diagnosis Cancer treatments Environmental tracers Age Determination
Nuclear fission Power generation
Nuclear Fusion The Sun
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