Nuclear Reactions Chemistry Mrs. Coyle. Part I Fission and Fusion.

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• Neutron-absorbing material such as cadmium, hafnium or boron, and are inserted or withdrawn from the core to control the rate of reaction, or to halt it.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