1. Nuclear Energy Nuclear Reactions Nuclear Fission / Nuclear Fusion Harnessing the Power of the Nucleus

2. 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

3. 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?

4. 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

5. 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

6. 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!!

7. Mass-Energy Equation Proposed by Einstein in 1905 (long before fission or fusion were discovered)  E = mc 2 E: Energy m: mass c: speed of light (3.0  10 8 m/s)

8. Mass-Energy Equation What does it mean? Tremendous amounts of energy are released from very small amounts of mass

9. 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

10. Chain Reactions (Nuclear Reactors) Fission reaction occurs Energy released turns water into steam Steam turns generator Electricity is created

11. 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?)

12. 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