Nuclear Energy

1
Chapter 30

• Nuclear Energy
• and
• Elementary Particles

2
Processes of Nuclear Energy

• Fission
• A nucleus of large mass number splits into two
  smaller nuclei
• Fusion
• Two light nuclei fuse to form a heavier nucleus
• Large amounts of energy are released in either
  case

3
Nuclear Fission

• A heavy nucleus splits into two smaller nuclei
• The total mass of the products is less than the
  original mass of the heavy nucleus
• First observed in 1939 by Otto Hahn and Fritz
  Strassman following basic studies by Fermi
• Lisa Meitner and Otto Frisch soon explained what
  had happened

4
Fission Equation

• Fission of 235U by a slow (low energy) neutron
• 236U is an intermediate, short-lived state
• Lasts about 10-12 s
• X and Y are called fission fragments
• Many combinations of X and Y satisfy the
  requirements of conservation of energy and charge

5
More About Fission of 235U

• About 90 different daughter nuclei can be formed
• Several neutrons are also produced in each
  fission event
• Example
• The fission fragments and the neutrons have a
  great deal of KE following the event

6
Sequence of Events in Fission

• The 235U nucleus captures a thermal (slow-moving)
  neutron
• This capture results in the formation of 236U,
  and the excess energy of this nucleus causes it
  to undergo violent oscillations
• The 236U nucleus becomes highly elongated, and
  the force of repulsion between the protons tends
  to increase the distortion
• The nucleus splits into two fragments, emitting
  several neutrons in the process

7
Sequence of Events in Fission Diagram
8
Energy in a Fission Process

• Binding energy for heavy nuclei is about 7.2 MeV
  per nucleon
• Binding energy for intermediate nuclei is about
  8.2 MeV per nucleon
• Therefore, the fission fragments have less mass
  than the nucleons in the original nuclei
• This decrease in mass per nucleon appears as
  released energy in the fission event

9
Energy, cont

• An estimate of the energy released
• Assume a total of 240 nucleons
• Releases about 1 MeV per nucleon
• 8.2 MeV 7.2 MeV
• Total energy released is about 240 Mev
• This is very large compared to the amount of
  energy released in chemical processes

10
Chain Reaction

• Neutrons are emitted when 235U undergoes fission
• These neutrons are then available to trigger
  fission in other nuclei
• This process is called a chain reaction
• If uncontrolled, a violent explosion can occur
• The principle behind the nuclear bomb, where 1 kg
  of U can release energy equal to about 20 000
  tons of TNT

11
Chain Reaction Diagram
12
Nuclear Reactor

• A nuclear reactor is a system designed to
  maintain a self-sustained chain reaction
• The reproduction constant, K, is defined as the
  average number of neutrons from each fission
  event that will cause another fission event
• The maximum value of K from uranium fission is
  2.5
• In practice, K is less than this
• A self-sustained reaction has K 1

13
K Values

• When K 1, the reactor is said to be critical
• The chain reaction is self-sustaining
• When K lt 1, the reactor is said to be subcritical
• The reaction dies out
• When K gt 1, the reactor is said to be
  supercritical
• A run-away chain reaction occurs

14
Basic Reactor Design

• Fuel elements consist of enriched uranium
• The moderator material helps to slow down the
  neutrons
• The control rods absorb neutrons

15
Reactor Design Considerations Neutron Leakage

• Loss (or leakage) of neutrons from the core
• These are not available to cause fission events
• The fraction lost is a function of the ratio of
  surface area to volume
• Small reactors have larger percentages lost
• If too many neutrons are lost, the reactor will
  not be able to operate

16
Reactor Design Considerations Neutron Energies

• Slow neutrons are more likely to cause fission
  events
• Most neutrons released in the fission process
  have energies of about 2 MeV
• In order to sustain the chain reaction, the
  neutrons must be slowed down
• A moderator surrounds the fuel
• Collisions with the atoms of the moderator slow
  the neutrons down as some kinetic energy is
  transferred
• Most modern reactors use heavy water as the
  moderator

17
Reactor Design Considerations Neutron Capture

• Neutrons may be captured by nuclei that do not
  undergo fission
• Most commonly, neutrons are captured by 238U
• The possibility of 238U capture is lower with
  slow neutrons
• The moderator helps minimize the capture of
  neutrons by 238U

18
Reactor Design Considerations Power Level
Control

• A method of control is needed to adjust the value
  of K to near 1
• If K gt1, the heat produced in the runaway
  reaction can melt the reactor
• Control rods are inserted into the core to
  control the power level
• Control rods are made of materials that are very
  efficient at absorbing neutrons
• Cadmium is an example
• By adjusting the number and position of the
  control rods, various power levels can be
  maintained

19
Pressurized Water Reactor Diagram
20
Pressurized Water Reactor Operation Notes

• This type of reactor is commonly used in electric
  power plants in the US
• Fission events in the reactor core supply heat to
  the water contained in the primary system
• The primary system is a closed system
• This water is maintained at a high pressure to
  keep it from boiling
• The hot water is pumped through a heat exchanger

21
Pressurized Water Reactor Operation Notes, cont

• The heat is transferred to the water contained in
  a secondary system
• This water is converted into steam
• The steam is used to drive a turbine-generator to
  create electric power
• The water in the secondary system is isolated
  from the water in the primary system
• This prevents contamination of the secondary
  water and steam by the radioactive nuclei in the
  core

22
Reactor Safety Containment

• Radiation exposure, and its potential health
  risks, are controlled by three levels of
  containment
• Reactor vessel
• Contains the fuel and radioactive fission
  products
• Reactor building
• Acts as a second containment structure should the
  reactor vessel rupture
• Location
• Reactor facilities are in remote locations

23
Reactor Safety Loss of Water

• If the water flow was interrupted, the nuclear
  reaction could stop immediately
• However, there could be enough residual heat to
  build up and melt the fuel elements
• The molten core could also melt through the
  containment vessel and into the ground
• Called the China Syndrome
• If the molten core struck ground water, a steam
  explosion could spread the radioactive material
  to areas surrounding the power plant
• Reactors are built with emergency cooling systems
  that automatically flood the core if coolant is
  lost

24
Reactor Safety Radioactive Materials

• Disposal of waste material
• Waste material contains long-lived, highly
  radioactive isotopes
• Must be stored over long periods in ways that
  protect the environment
• Present solution is sealing the waste in
  waterproof containers and burying them in deep
  salt mines
• Transportation of fuel and wastes
• Accidents during transportation could expose the
  public to harmful levels of radiation
• Department of Energy requires crash tests and
  manufacturers must demonstrate that their
  containers will not rupture during high speed
  collisions

25
Nuclear Fusion

• Nuclear fusion occurs when two light nuclei
  combine to form a heavier nucleus
• The mass of the final nucleus is less than the
  masses of the original nuclei
• This loss of mass is accompanied by a release of
  energy

26
Fusion in the Sun

• All stars generate energy through fusion
• The Sun, along with about 90 of other stars,
  fuses hydrogen
• Some stars fuse heavier elements
• Two conditions must be met before fusion can
  occur in a star
• The temperature must be high enough
• The density of the nuclei must be high enough to
  ensure a high rate of collisions

27
Proton-Proton Cycle

• The proton-proton cycle is a series of three
  nuclear reactions believed to operate in the Sun
• Energy liberated is primarily in the form of
  gamma rays, positrons and neutrinos
• 21H is deuterium, and may be written as 21D

28
Fusion Reactors

• Energy releasing fusion reactions are called
  thermonuclear fusion reactions
• A great deal of effort is being directed at
  developing a sustained and controllable
  thermonuclear reaction
• A thermonuclear reactor that can deliver a net
  power output over a reasonable time interval is
  not yet a reality

29
Advantages of a Fusion Reactor

• Inexpensive fuel source
• Water is the ultimate fuel source
• If deuterium is used as fuel, 0.06 g of it can be
  extracted from 1 gal of water for about 4 cents
• Comparatively few radioactive by-products are
  formed

30
Considerations for a Fusion Reactor

• The proton-proton cycle is not feasible for a
  fusion reactor
• The high temperature and density required are not
  suitable for a fusion reactor
• The most promising reactions involve deuterium
  (D) and tritium (T)

31
Considerations for a Fusion Reactor, cont

• Deuterium is available in almost unlimited
  quantities in water and is inexpensive to extract
• Tritium is radioactive and must be produced
  artificially
• The Coulomb repulsion between two charged nuclei
  must be overcome before they can fuse

32
Requirements for Successful Thermonuclear Reactor

• High temperature ? 108 K
• Needed to give nuclei enough energy to overcome
  Coulomb forces
• At these temperatures, the atoms are ionized,
  forming a plasma
• Plasma ion density, n
• The number of ions present
• Plasma confinement time, ?
• The time the interacting ions are maintained at a
  temperature equal to or greater than that
  required for the reaction to proceed successfully

33
Lawsons Criteria

• Lawsons criteria states that a net power output
  in a fusion reactor is possible under the
  following conditions
• n? ? 1014 s/cm3 for deuterium-tritium
• n? ? 1016 s/cm3 for deuterium-deuterium
• The plasma confinement time is still a problem

34
Magnetic Confinement

• One magnetic confinement device is called a
  tokamak
• Two magnetic fields confine the plasma inside the
  doughnut
• A strong magnetic field is produced in the
  windings
• A weak magnetic field is produced in the toroid
• The field lines are helical, spiral around the
  plasma, and prevent it from touching the wall of
  the vacuum chamber

35
Some Fusion Reactors

• TFTR
• Tokamak Fusion Test Reactor
• Princeton
• Central ion temperature of 510 million degrees C
• The nt values were close to Lawson criteria
• JET
• Tokamak at Abington, England
• 6 x 1017 DT fusions per second were achieved

36
Current Research in Fusion Reactors

• NSTX National Spherical Torus Experiment
• Produces a spherical plasma with a hole in the
  center
• Is able to confine the plasma with a high
  pressure
• ITER International Thermonuclear Experimental
  Reactor
• An international collaboration involving four
  major fusion programs is working on building this
  reactor
• It will address remaining technological and
  scientific issues concerning the feasibility of
  fusion power

37
Other Methods of Creating Fusion Events

• Inertial laser confinement
• Fuel is put into the form of a small pellet
• It is collapsed by ultrahigh power lasers
• Inertial electrostatic confinement
• Positively charged particles are rapidly
  attracted toward an negatively charged grid
• Some of the positive particles collide and fuse

38
Elementary Particles

• Atoms
• From the Greek for indivisible
• Were once thought to the elementary particles
• Atom constituents
• Proton, neutron, and electron
• Were viewed as elementary because they are very
  stable

39
Discovery of New Particles

• New particles
• Beginning in 1937, many new particles were
  discovered in experiments involving high-energy
  collisions
• Characteristically unstable with short lifetimes
• Over 300 have been cataloged
• A pattern was needed to understand all these new
  particles

40
Quarks

• Physicists recognize that most particles are made
  up of quarks
• Exceptions include photons, electrons and a few
  others
• The quark model has reduced the array of
  particles to a manageable few
• The quark model has successfully predicted new
  quark combinations that were subsequently found
  in many experiments

41
Fundamental Forces

• All particles in nature are subject to four
  fundamental forces
• Strong force
• Electromagnetic force
• Weak force
• Gravitational force

42
Strong Force

• Is responsible for the tight binding of the
  quarks to form neutrons and protons
• Also responsible for the nuclear force binding
  the neutrons and the protons together in the
  nucleus
• Strongest of all the fundamental forces
• Very short-ranged
• Less than 10-15 m

43
Electromagnetic Force

• Is responsible for the binding of atoms and
  molecules
• About 10-2 times the strength of the strong force
• A long-range force that decreases in strength as
  the inverse square of the separation between
  interacting particles

44
Weak Force

• Is responsible for instability in certain nuclei
• Is responsible for beta decay
• A short-ranged force
• Its strength is about 10-6 times that of the
  strong force
• Scientists now believe the weak and
  electromagnetic forces are two manifestations of
  a single force, the electroweak force

45
Gravitational Force

• A familiar force that holds the planets, stars
  and galaxies together
• Its effect on elementary particles is negligible
• A long-range force
• It is about 10-43 times the strength of the
  strong force
• Weakest of the four fundamental forces

46
Explanation of Forces

• Forces between particles are often described in
  terms of the actions of field particles or quanta
• For electromagnetic force, the photon is the
  field particle
• The electromagnetic force is mediated, or
  carried, by photons

47
Forces and Mediating Particles (also see table
30.1)
Interaction (force) Mediating Field Particle
Strong Gluon
Electromagnetic Photon
Weak W? and Z0
Gravitational Gravitons
48
Paul Adrien Maurice Dirac

• 1902 1984
• Instrumental in understanding antimatter
• Aided in the unification of quantum mechanics and
  relativity
• Contributions to quantum physics and cosmology
• Nobel Prize in 1933

49
Antiparticles

• For every particle, there is an antiparticle
• From Diracs version of quantum mechanics that
  incorporated special relativity
• An antiparticle has the same mass as the
  particle, but the opposite charge
• The positron (electrons antiparticle) was
  discovered by Anderson in 1932
• Since then, it has been observed in numerous
  experiments
• Practically every known elementary particle has a
  distinct antiparticle
• Exceptions the photon and the neutral pi
  particles are their own antiparticles

50
Hideki Yukawa

• 1907 1981
• Predicted the existence of mesons
• Nobel Prize in 1949

51
Mesons

• Developed from a theory to explain the strong
  nuclear force
• Background notes
• Two atoms can form a covalent bond by the
  exchange of electrons
• In electromagnetic interactions, charged
  particles interact by exchanging a photon
• A new particle was proposed to explain the strong
  nuclear force
• It was called a meson

52
Mesons, cont

• The proposed particle would have a mass about 200
  times that of the electron
• Efforts to establish the existence of the
  particle were done by studying cosmic rays in the
  1930s
• Actually discovered multiple particles
• Pi meson (called pion)
• Muon
• Plays no role in the strong interaction

53
Pion

• There are three varieties of pions
• ? and ?-
• Mass of 139.6 MeV/c2
• ?0
• Mass of 135.0 MeV/c2
• Pions are very unstable
• ?- decays into a muon and an antineutrino with a
  lifetime of about 2.6 x10-8 s

54
Richard Feynmann

• 1918 1988
• Contributions include
• Work on the Manhattan Project
• Invention of diagrams to represent particle
  interactions
• Theory of weak interactions
• Reformation of quantum mechanics
• Superfluid helium
• Challenger investigation
• Shared Nobel Prize in 1965

55
Feynman Diagrams

• A graphical representation of the interaction
  between two particles
• Feynman diagrams are named for Richard Feynman
  who developed them

56
Feynman Diagram Two Electrons

• The photon is the field particle that mediates
  the interaction
• The photon transfers energy and momentum from one
  electron to the other
• The photon is called a virtual photon
• It can never be detected directly because it is
  absorbed by the second electron very shortly
  after being emitted by the first electron

57
The Virtual Photon

• The existence of the virtual photon would be
  expected to violate the law of conservation of
  energy
• But, due to the uncertainty principle and its
  very short lifetime, the photons excess energy
  is less than the uncertainty in its energy
• The virtual photon can exist for short time
  intervals, such that ?E ?t ? h

58
Feynman Diagram Proton and Neutron

• The exchange is via the nuclear force
• The existence of the pion is allowed in spite of
  conservation of energy if this energy is
  surrendered in a short enough time
• Analysis predicts the rest energy of the pion to
  be 130 MeV / c2
• This is in close agreement with experimental
  results

59
Classification of Particles

• Two broad categories
• Classified by interactions
• Hadrons interact through strong force
• Leptons interact through weak force

60
Hadrons

• Interact through the strong force
• Two subclasses
• Mesons
• Decay finally into electrons, positrons,
  neutrinos and photons
• Integer spins
• Baryons
• Masses equal to or greater than a proton
• Noninteger spin values
• Decay into end products that include a proton
  (except for the proton)
• Composed of quarks

61
Leptons

• Interact through weak force
• All have spin of ½
• Leptons appear truly elementary
• No substructure
• Point-like particles
• Scientists currently believe only six leptons
  exist, along with their antiparticles
• Electron and electron neutrino
• Muon and its neutrino
• Tau and its neutrino

62
Conservation Laws

• A number of conservation laws are important in
  the study of elementary particles
• Two new ones are
• Conservation of Baryon Number
• Conservation of Lepton Number

63
Conservation of Baryon Number

• Whenever a baryon is created in a reaction or a
  decay, an antibaryon is also created
• B is the Baryon Number
• B 1 for baryons
• B -1 for antibaryons
• B 0 for all other particles
• The sum of the baryon numbers before a reaction
  or a decay must equal the sum of baryon numbers
  after the process

64
Conservation of Lepton Number

• There are three conservation laws, one for each
  variety of lepton
• Law of Conservation of Electron-Lepton Number
  states that the sum of electron-lepton numbers
  before a reaction or a decay must equal the sum
  of the electron-lepton number after the process

65
Conservation of Lepton Number, cont

• Assigning electron-lepton numbers
• Le 1 for the electron and the electron neutrino
• Le -1 for the positron and the electron
  antineutrino
• Le 0 for all other particles
• Similarly, when a process involves muons,
  muon-lepton number must be conserved and when a
  process involves tau particles, tau-lepton
  numbers must be conserved
• Muon- and tau-lepton numbers are assigned
  similarly to electron-lepton numbers

66
Strange Particles

• Some particles discovered in the 1950s were
  found to exhibit unusual properties in their
  production and decay and were given the name
  strange particles
• Peculiar features include
• Always produced in pairs
• Although produced by the strong interaction, they
  do not decay into particles that interact via the
  strong interaction, but instead into particles
  that interact via weak interactions
• They decay much more slowly than particles
  decaying via strong interactions

67
Strangeness

• To explain these unusual properties, a new law,
  conservation of strangeness, was introduced
• Also needed a new quantum number, S
• The Law of Conservation of Strangeness states
  that the sum of strangeness numbers before a
  reaction or a decay must equal the sum of the
  strangeness numbers after the process
• Strong and electromagnetic interactions obey the
  law of conservation of strangeness, but the weak
  interactions do not

68
Bubble ChamberExample

• The dashed lines represent neutral particles
• At the bottom,
• ?- p ? ?0 K0
• Then ?0 ? ?- p and
• K0 ? ? µ- ?µ

69
Murray Gell-Mann

• 1929
• Worked on theoretical studies of subatomic
  particles
• Nobel Prize in 1969

70
The Eightfold Way

• Many classification schemes have been proposed to
  group particles into families
• These schemes are based on spin, baryon number,
  strangeness, etc.
• The eightfold way is a symmetric pattern proposed
  by Gell-Mann and Neeman
• There are many symmetrical patterns that can be
  developed
• The patterns of the eightfold way have much in
  common with the periodic table
• Including predicting missing particles

71
An Eightfold Way for Baryons

• A hexagonal pattern for the eight spin ½ baryons
• Strangeness vs. charge is plotted on a sloping
  coordinate system
• Six of the baryons form a hexagon with the other
  two particles at its center

72
An Eightfold Way for Mesons

• The mesons with spins of 0 can be plotted
• Strangeness vs. charge on a sloping coordinate
  system is plotted
• A hexagonal pattern emerges
• The particles and their antiparticles are on
  opposite sides on the perimeter of the hexagon
• The remaining three mesons are at the center

73
Quarks

• Hadrons are complex particles with size and
  structure
• Hadrons decay into other hadrons
• There are many different hadrons
• Quarks are proposed as the elementary particles
  that constitute the hadrons
• Originally proposed independently by Gell-Mann
  and Zweig

74
Original Quark Model

• Three types
• u up
• d down
• s originally sideways, now strange
• Associated with each quark is an antiquark
• The antiquark has opposite charge, baryon number
  and strangeness

75
Original Quark Model, cont

• Quarks have fractional electrical charges
• 1/3 e and 2/3 e
• All ordinary matter consists of just u and d
  quarks

76
Original Quark Model Rules

• All the hadrons at the time of the original
  proposal were explained by three rules
• Mesons consist of one quark and one antiquark
• This gives them a baryon number of 0
• Baryons consist of three quarks
• Antibaryons consist of three antiquarks

77
Additions to the Original Quark Model Charm

• Another quark was needed to account for some
  discrepancies between predictions of the model
  and experimental results
• Charm would be conserved in strong and
  electromagnetic interactions, but not in weak
  interactions
• In 1974, a new meson, the J/? was discovered that
  was shown to be a charm quark and charm antiquark
  pair

78
More Additions Top and Bottom

• Discovery led to the need for a more elaborate
  quark model
• This need led to the proposal of two new quarks
• t top (or truth)
• b bottom (or beauty)
• Added quantum numbers of topness and bottomness
• Verification
• b quark was found in a Y meson in 1977
• t quark was found in 1995 at Fermilab

79
Numbers of Particles

• At the present, physicists believe the building
  blocks of matter are complete
• Six quarks with their antiparticles
• Six leptons with their antiparticles
• See table 30.5

80
Color

• Isolated quarks
• Physicist now believe that quarks are permanently
  confined inside ordinary particles
• No isolated quarks have been observed
  experimentally
• The explanation is a force called the color force
• Color force increases with increasing distance
• This prevents the quarks from becoming isolated
  particles

81
Colored Quarks

• Color charge occurs in red, blue, or green
• Antiquarks have colors of antired, antiblue, or
  antigreen
• Color obeys the Exclusion Principle
• A combination of quarks of each color produces
  white (or colorless)
• Baryons and mesons are always colorless

82
Quark Structure of a Meson

• A green quark is attracted to an antigreen quark
• The quark antiquark pair forms a meson
• The resulting meson is colorless

83
Quark Structure of a Baryon

• Quarks of different colors attract each other
• The quark triplet forms a baryon
• The baryon is colorless

84
Quantum Chromodynamics (QCD)

• QCD gave a new theory of how quarks interact with
  each other by means of color charge
• The strong force between quarks is often called
  the color force
• The strong force between quarks is carried by
  gluons
• Gluons are massless particles
• There are 8 gluons, all with color charge
• When a quark emits or absorbs a gluon, its color
  changes

85
More About Color Charge

• Like colors repel and opposite colors attract
• Different colors also attract, but not as
  strongly as a color and its anticolor
• The color force between color-neutral hadrons is
  negligible at large separations
• The strong color force between the constituent
  quarks does not exactly cancel at small
  separations
• This residual strong force is the nuclear force
  that binds the protons and neutrons to form nuclei

86
QCD Explanation of a Neutron-Proton Interaction

• Each quark within the proton and neutron is
  continually emitting and absorbing virtual gluons
• Also creating and annihilating virtual
  quark-antiquark pairs
• When close enough, these virtual gluons and
  quarks can be exchanged, producing the strong
  force

87
Weak Interaction

• The weak interaction is an extremely short-ranged
  force
• This short range implies the mediating particles
  are very massive
• The weak interaction is responsible for the decay
  of c, s, b, and t quarks into u and d quarks
• Also responsible for the decay of ? and ? leptons
  into electrons

88
Weak Interaction, cont

• The weak interaction is very important because it
  governs the stability of the basic particles of
  matter
• The weak interaction is not symmetrical
• Not symmetrical under mirror reflection
• Not symmetrical under charge exchange

89
Electroweak Theory

• The electroweak theory unifies electromagnetic
  and weak interactions
• The theory postulates that the weak and
  electromagnetic interactions have the strength at
  very high particle energies
• Viewed as two different manifestations of a
  single interaction

90
The Standard Model

• A combination of the electroweak theory and QCD
  form the standard model
• Essential ingredients of the standard model
• The strong force, mediated by gluons, holds the
  quarks together to form composite particles
• Leptons participate only in electromagnetic and
  weak interactions
• The electromagnetic force is mediated by photons
• The weak force is mediated by W and Z bosons

91
The Standard Model Chart
92
Mediator Masses

• Why does the photon have no mass while the W and
  Z bosons do have mass?
• Not answered by the Standard Model
• The difference in behavior between low and high
  energies is called symmetry breaking
• The Higgs boson has been proposed to account for
  the masses
• Large colliders are necessary to achieve the
  energy needed to find the Higgs boson

93
Grand Unification Theory (GUT)

• Builds on the success of the electroweak theory
• Attempted to combine electroweak and strong
  interactions
• One version considers leptons and quarks as
  members of the same family
• They are able to change into each other by
  exchanging an appropriate particle

94
The Big Bang

• This theory of cosmology states that during the
  first few minutes after the creation of the
  universe all four interactions were unified
• All matter was contained in a quark soup
• As time increased and temperature decreased, the
  forces broke apart
• Starting as a radiation dominated universe, as
  the universe cooled it changed to a matter
  dominated universe

95
A Brief History of the Universe
96
George Gamow

• 1904 1968
• Among the first to look at the first half hour of
  the universe
• Predicted
• Abundances of hydrogen and helium
• Radiation should still be present and have an
  apparent temperature of about 5 K

97
Cosmic Background Radiation (CBR)

• CBR represents the cosmic glow left over from
  the Big Bang
• The radiation had equal strengths in all
  directions
• The curve fits a blackbody at ?3K
• There are small irregularities that allowed for
  the formation of galaxies and other objects

98
Connection Between Particle Physics and Cosmology

• Observations of events that occur when two
  particles collide in an accelerator are essential
  to understanding the early moments of cosmic
  history
• There are many common goals between the two fields

99
Some Questions

• Why so little antimatter in the Universe?
• Do neutrinos have mass?
• How do they contribute to the dark mass in the
  universe?
• Explanation of why the expansion of the universe
  is accelerating?
• Is there a kind of antigravity force acting
  between widely separated galaxies?
• Is it possible to unify electroweak and strong
  forces?
• Why do quark and leptons form similar but
  distinct families?

100
More Questions

• Are muons the same as electrons, except for their
  mass?
• Why are some particles charged and others
  neutral?
• Why do quarks carry fractional charge?
• What determines the masses of fundamental
  particles?
• Do leptons and quarks have a substructure?