great ideas in science: lecture 7 – nuclear reactions

Great Ideas in Science:Great Ideas in Science:Lecture 7 – Nuclear ReactionsLecture 7 – Nuclear Reactions

Professor Robert HazenProfessor Robert Hazen

UNIV 301UNIV 301

Great Idea: Nuclear energy arises from the conversion of mass into energy.

Nuclear ReactionsNuclear Reactions

Key Idea: Key Idea: Nuclear reactionsNuclear reactions result result from the rearrangement of an atomfrom the rearrangement of an atom’’s s protons and neutrons (i.e. the nucleus)protons and neutrons (i.e. the nucleus)

Key Words:Key Words:• ProtonProton• NeutronNeutron• NucleusNucleus• IsotopeIsotope• RadioactivityRadioactivity• Nuclear FissionNuclear Fission• Nuclear FusionNuclear Fusion

The Building Blocks The Building Blocks of Matterof Matter

Of what is matter made?Of what is matter made?• AtomsAtoms• Nuclei and electronsNuclei and electrons• QuarksQuarks

Key Words About AtomsKey Words About Atoms

Atom:Atom: Any object with a nucleus Any object with a nucleus and electronsand electrons

Element:Element: An atom with a known An atom with a known number of protons (the atomic number of protons (the atomic number)number)

Ion:Ion: An electronically-charged An electronically-charged atom with a different number of atom with a different number of protons (+) and electrons (-)protons (+) and electrons (-)

Isotope: Isotope: An element with a An element with a known number of neutronsknown number of neutrons

The Structure of the AtomThe Structure of the Atom Electrons in shells (energy levels)Electrons in shells (energy levels)

Negatively chargedNegatively charged Shift during chemical reactionsShift during chemical reactions

The Structure of the AtomThe Structure of the Atom Electrons in shells (energy levels)Electrons in shells (energy levels)

Negatively chargedNegatively charged Shift during chemical reactionsShift during chemical reactions

Central dense nucleusCentral dense nucleus Composed of protons and neutrons Composed of protons and neutrons Positively chargedPositively charged Nucleus - Stays put in chemical reactionsNucleus - Stays put in chemical reactions

Isotopes: Hydrogen & CarbonIsotopes: Hydrogen & Carbon H-1 – 1 protonH-1 – 1 proton H-2 – 1 p & 1 neutron (Deuterium)H-2 – 1 p & 1 neutron (Deuterium) H-3 – 1 p & 2 n (Tritium)H-3 – 1 p & 2 n (Tritium)

C-12 – 6p & 6nC-12 – 6p & 6n C-13 – 6p & 7nC-13 – 6p & 7n C-14 – 6p & 8n (radioactive)C-14 – 6p & 8n (radioactive)

For any given element the number For any given element the number of protons is fixed of protons is fixed

Four Fates of IsotopesFour Fates of Isotopes

An isotope may be stableAn isotope may be stable

An isotope may be radioactiveAn isotope may be radioactive

An isotope may be split apart An isotope may be split apart by fissionby fission

An isotope may combine with An isotope may combine with another by fusionanother by fusion

Chart of the Isotopes (Z vs. N)Chart of the Isotopes (Z vs. N)

Stable IsotopesStable Isotopes 99.999+% of all the atoms around 99.999+% of all the atoms around

usus Examples are carbon-12 and Examples are carbon-12 and

carbon-13carbon-13 Different isotopes donDifferent isotopes don’’t affect t affect

chemical reactions.chemical reactions. Used in scientific research to Used in scientific research to

track chemical reactions (2 ways)track chemical reactions (2 ways)• As tracersAs tracers• FractionationFractionation

Radioactivity or Radioactive Radioactivity or Radioactive Decay (three kinds)Decay (three kinds)

Alpha radiationAlpha radiation

Beta radiationBeta radiation

Gamma radiationGamma radiation

The spontaneous emission of an energetic particle by a nucleus

Most Kinds of Isotopes Most Kinds of Isotopes are Radioactiveare Radioactive

STABLE

RADIOACTIVE

Alpha RadiationAlpha Radiation Atom spontaneously loses 2 protons and Atom spontaneously loses 2 protons and

2 neutrons (= a Helium-4 nucleus)2 neutrons (= a Helium-4 nucleus)

Alpha RadiationAlpha Radiation Atom spontaneously loses 2 protons and Atom spontaneously loses 2 protons and

2 neutrons (= a Helium-4 nucleus)2 neutrons (= a Helium-4 nucleus) Uranium-238 Uranium-238 Thorium-234 + 2n + 2p Thorium-234 + 2n + 2p

Beta RadiationBeta Radiation One neutron spontaneously becomes One neutron spontaneously becomes

a proton plus an electrona proton plus an electron Thorium-234 Thorium-234 Proactinium-234 Proactinium-234

Gamma RadiationGamma Radiation Atom spontaneously emits a gamma Atom spontaneously emits a gamma

ray (electromagnetic radiation)ray (electromagnetic radiation) Uranium-238* Uranium-238* Uranium-238 + Uranium-238 + γγ

Gamma RadiationGamma Radiation Atom spontaneously emits a gamma Atom spontaneously emits a gamma

ray (electromagnetic radiation)ray (electromagnetic radiation) Uranium-238* Uranium-238* Thorium 234 + Thorium 234 + γγ

SUMMARY: The Three Kinds SUMMARY: The Three Kinds of Radioactive Decayof Radioactive Decay

Alpha DecayAlpha Decay• Release of Release of αα particle with 2 particle with 2

protons and 2 neutronsprotons and 2 neutrons Beta DecayBeta Decay

• Neutron becomes a protonNeutron becomes a proton• Emission of electron (Emission of electron (ββ-ray)-ray)

Gamma RadiationGamma Radiation• Electromagnetic radiationElectromagnetic radiation

Radioactivity and HealthRadioactivity and Health

IonizationIonization• Stripping off Stripping off

electronselectrons

Long-term effectsLong-term effects• CancerCancer• Birth defectsBirth defects

Half-LifeHalf-Life The average time for decay of ½ The average time for decay of ½

batch of radioactive isotopesbatch of radioactive isotopes

Wide range of half-livesWide range of half-lives

Radiometric DatingRadiometric Dating1.1. Know half-life of isotopeKnow half-life of isotope

2.2. Know how much was thereKnow how much was there

3.3. Measure whatMeasure what’’s lefts left

Carbon-14: Half-life = 5730 yearsCarbon-14: Half-life = 5730 years

Radiometric DatingRadiometric DatingApplications to geologyApplications to geology

• Need longer half-livesNeed longer half-lives• Uranium, potassiumUranium, potassium

Radioactive Decay Chain (radon)Radioactive Decay Chain (radon)


An isotope may be stableAn isotope may be stable An isotope may be radioactiveAn isotope may be radioactive An isotope may be split apart An isotope may be split apart

by fissionby fission An isotope may combine with An isotope may combine with

another by fusionanother by fusion

Nuclear Fission (Splitting)Nuclear Fission (Splitting) Fission = Fission =

Splitting of Splitting of nucleusnucleus

A nuclear reactor A nuclear reactor converts mass to converts mass to energyenergy

Nuclear Fission (Splitting)Nuclear Fission (Splitting)

Nuclear Fission – The Atom BombNuclear Fission – The Atom Bomb

Hiroshima – August 6, 1945Hiroshima – August 6, 1945

Nuclear Fission – The Atom BombNuclear Fission – The Atom Bomb

Yucca Mountain, Nevada Yucca Mountain, Nevada (NIMBY)(NIMBY)


An isotope may be stableAn isotope may be stable An isotope may be An isotope may be

radioactiveradioactive An isotope may be split apart An isotope may be split apart

by fissionby fission An isotope may combine with An isotope may combine with

another by fusionanother by fusion

Nuclear Fusion (Fusing)Nuclear Fusion (Fusing)

• Hydrogen atoms Hydrogen atoms combine to form heliumcombine to form helium

• Some mass is converted Some mass is converted into energyinto energy

Nuclear Fusion – Hydrogen BombNuclear Fusion – Hydrogen Bomb

Stars are Giant Fusion ReactorsStars are Giant Fusion Reactors

http://www.earth.northwestern.edu/people/seth/107/Solar/Image12.gif

Fates of StarsFates of Stars

Benefits of Isotopes Benefits of Isotopes Stable IsotopesStable Isotopes

• Medical ResearchMedical Research• Environmental TracersEnvironmental Tracers

Radioactive IsotopesRadioactive Isotopes• Medical diagnosisMedical diagnosis• Cancer treatmentsCancer treatments• Environmental tracersEnvironmental tracers• Age DeterminationAge Determination

Nuclear fissionNuclear fission• Power generationPower generation

Nuclear FusionNuclear Fusion• The SunThe Sun

great ideas in science: lecture 7 – nuclear reactions

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decay of batch

atoms protons

known number of protons

different number of

nuclear energy

electrons isotope

gamma radiationatom

atom electrons