Nuclear Reactions

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Nuclear Reactions

• ChemistryMrs. Coyle

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Part I

• Fission and Fusion

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Transmutations

• When a nucleus of an element is transformed to a
  nucleus of another element.

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Transmutations

• Can occur through
• Decay (Spontaneously)
• Nuclear Reactions (Fusion and Fission)

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Nuclear Reactions

• Fission
• Fusion

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Nuclear Fission

• Enrico Fermi (USA) 1930s
• Lise Meitner, Strassman, Hahn (Germany)
• Bombarding neutrons at 235U or 239Pu causes
  fission (splitting) of the nucleus producing new
  neutrons that then cause more fission in a chain
  reaction.
• Huge amounts of energy (mostly kinetic energy of
  fragments) is released

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Nuclear Fission
Chain Reaction
Neutron bombardment

• n 235U ? 236U ?XY n energy

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Nuclear Fission

• 235U is a rather rare isotope(0.7) of the more
  abundant 238U which does not undergo fission.
• Nuclear Bomb
• Nuclear Power Plants

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Nuclear Fusion

• Suns energy comes from fusing of hydrogen to
  form helium
• Product has higher mass number than reactant

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H H ? He n energy
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Part II

• Nuclear Energy

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Emc

• Mass Energy Equivalence
• Special Relativity

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Nuclear Energy used to make Electricity

• 16 of the world's electricity is produced from
  nuclear energy .
• In the US 20 of electricity is made by about
  130 nuclear reactor sites.

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Nuclear Reactor at Indian Point, NY
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Main Parts of a Nuclear Reactor

• Fuel Rods
• Neutron Moderator
• Control rods
• Coolant
• Containment

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Fuel Rods

• Pellets of uranium oxide arranged in tubes in the
  reactor core. (Plutonium is also sometimes used
  as fuel).
• About 260 fuel rods form an assembly.

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Neutron Moderator

• Slows down the neutrons released from fission so
  that they are captured by the fuel to continue
  the chain reaction.
• Water or graphite.

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Control Rods

• Neutron-absorbing material such as cadmium,
  hafnium or boron, and are inserted or withdrawn
  from the core to control the rate of reaction, or
  to halt it.

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Coolant

• A liquid or gas circulating through the core so
  as to transfer the heat from it.

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Steam Generator

• The heat from the reactor is used to make steam
  to run the turbine to generate electricity.

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Containment

• A one meter thick concrete and steel structure
  around the reactor core.
• Protects the core.
• Protects the environment from radiation in case
  of malfunction.

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Refueling

• Every 1-2 years fuel rods are replaced.
• Spent fuel rods are still radioactive (nuclear
  waste).

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Nuclear Reactors
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Part III

• Detecting radiation

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The Geiger Counter

• Radiation detector
• Hans Geiger

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Operation of Geiger Counter

• The radiation ionizes a gas (argon) and
• frees electrons.
• The electrons are attracted to the positive
  electrode, that ionize gas again etc, producing a
  current pulse.
• This is amplified and heard as a sound.

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Units of Radiation

• measured in rads (radiation absorbed dose), a
  unit of absorbed energy
• 1 rad 0.01 joule of radiant energy
  absorbed/kilogram of tissue
• 1 rem (roentgen equivalent man) is the radiation
  dosage based on potential damage

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Cosmic Rays

• Cosmic rays are of two types
• high-energy particles.
• high-frequency electromagnetic radiation (gamma
  rays).
• They affect us indirectly by transforming
  nitrogen atoms in the air to radioactive
  carbon-14, which ends up in plants we consume.

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