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
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
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
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
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 – The Atom BombNuclear Fission – The Atom Bomb
Hiroshima – August 6, 1945Hiroshima – August 6, 1945
Four Fates of IsotopesFour Fates of Isotopes
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
Stars are Giant Fusion ReactorsStars are Giant Fusion Reactors
http://www.earth.northwestern.edu/people/seth/107/Solar/Image12.gif
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