Nuclear Reactions
ChemistryMrs. Coyle
Part I
• Fission and Fusion
Transmutations
• When a nucleus of an element is transformed to a nucleus of another element.
Transmutations
• Can occur through:
– Decay (Spontaneously)– Nuclear Reactions (Fusion and Fission)
Nuclear Reactions
• Fission
• Fusion
Nuclear Fission
• Enrico Fermi (USA) 1930’s
• 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
Nuclear Fission
n + 235U 236U X+Y +n + energy
Chain ReactionNeutron bombardment
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
Nuclear Fusion
• Sun’s energy comes from fusing of hydrogen to form helium
• Product has higher mass number than reactant
H + H He +n + energy
Part II
• Nuclear Energy
• Mass – Energy Equivalence
• Special Relativity
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.
Nuclear Reactor at Indian Point, NY
Main Parts of a Nuclear Reactor
• Fuel Rods
• Neutron Moderator
• Control rods
• Coolant
• Containment
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.
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.
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• Neutron-absorbing material such as cadmium, hafnium or boron, and are inserted or withdrawn from the core to control the rate of reaction, or to halt it.
Coolant
• A liquid or gas circulating through the core so as to transfer the heat from it.
Steam Generator
• The heat from the reactor is used to make steam to run the turbine to generate electricity.
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.
Refueling
• Every 1-2 years fuel rods are replaced.
• Spent fuel rods are still radioactive (nuclear waste).
Nuclear Reactors
Part III
• Detecting radiation
The Geiger Counter
• Radiation detector
• Hans Geiger
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.
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
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.
