07 Stripped Nuclear

8/12/2019 07 Stripped Nuclear

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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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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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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

07 Stripped Nuclear

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