Nuclear EnergyNuclear Reactions

Nuclear Fission / Nuclear FusionHarnessing the Power of the Nucleus

Objectives 10.4.1) Explain why the nucleus of

some elements is unstable 10.4.2) Describe the process of

nuclear fission, including the reactants & products

10.4.3) Explain how a nuclear chain reaction occurs

10.4.4) Describe the process of nuclear fusion, including the conditions required for fusion to occur

Unstable Atomic Nuclei

Shortly after the discovery of radioactivity by Becquerel, scientists discovered that the nucleus of an atom contained huge amounts of potential energy

WHY?

Unstable Atomic Nuclei

A nucleus becomes unstable when the strong nuclear force is not strong enough to overcome the repulsion of protons

All atoms with atomic numbers greater than 83 are radioactive Radioactive: unstable nucleus emits

energy when it breaks into smaller parts

Nuclear Fission

Proposed by Lise Meitner & Otto Frisch in 1939

Definition: Splitting of a larger atomic nucleus into smaller isotopes

Tremendous amounts of energy are released from very small amounts of mass

Fast moving neutron runs into a radioactive nucleus

Why use a neutron?

Neutrons have no charge – their motion will not change as they

move closer to the nucleus

Two smaller nuclei that are not radioactive are created

Also released: 2 or 3 stray neutrons and LOTS of

energy!!

Mass-Energy Equation

Proposed by Einstein in 1905 (long before fission or fusion were discovered) E = mc2

E: Energy m: mass c: speed of light (3.0108 m/s)

Mass-Energy Equation

What does it mean? Tremendous amounts of energy

are released from very small amounts of mass

Chain Reactions

The neutrons released during fission can be used to split other unstable atoms

Left unchecked, a chain reaction can produce huge amounts of energy Atomic Bombs

Nuclear Reactors use a controlled chain reaction where the number of neutrons that split other unstable atoms is limited

Chain Reactions(Nuclear Reactors)

Fission reaction occurs

Energy released

turns water into

steam

Steam turns generator

Electricity is created

Nuclear Fusion

Two small nuclei are combined to form a nucleus with a greater atomic number

A small amount of mass is converted to energy during fusion Mass-Energy equation says small amounts

of mass produces large amounts of energy

Fusion requires extremely high temperatures (WHY?)

Both small nuclei are positively

charged – they repel

The only way to get them to stay close together is to raise the

temperature really high to make them move really fast

When they combine, a small amount of mass turns to a HUGE

amount of energy