# Nuclear Physics

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A series of free High School Physics Video Lessons.

In this lesson, we will learn

• Nuclear Fission
• Fission Reactors
• Nuclear Fusion
• Mass-Energy Equivalence

### Fission

Fission involves splitting atomic nuclei into fragments. Atoms with mass numbers close to 60 have been found to be the most stable. Atoms with mass numbers lower than 60 undergo fusion while atoms with higher mass numbers undergo fission. The energy needed to break one mole of nuclei into individual nucleons is called binding energy.

How radioactive substances undergo fission to reach more stable states.
Nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts, often producing free neutrons and lighter nuclei, which may eventually produce photons (in the form of gamma rays). Fission of heavy elements is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments (heating the bulk material where fission takes place). Fission is a form of nuclear transmutation because the resulting fragments are not the same element as the original atom. An array of 138 mousetraps are set off in a chain reaction. Ping-pong balls help visualize both neutrons and the release of energy.

### Fission Reactors

Fission reactors use fissile materials to initiate fission reactions. A moderator is used to slow the reaction. If the reaction gets too hot the fuel melts and the reactor no longer functions. Control rods absorb neutrons from within the fuel to keep the fissile material from overheating. The thermal medium is either water or sodium and is used to harness the energy. The hot thermal medium boils and in its gaseous state is used to run a turbine and generate electricity. Then the thermal medium is cooled in a condenser for reuse.

An explanation of fission reactors.
Nuclear reactor produces heat from nuclear fission.

### Fusion

Fusion involves the combining of atomic nuclei. Atoms with mass numbers lower than 60 undergo fusion while atoms with higher mass numbers undergo fission. The energy needed to break one mole of nuclei into individual nucleons is called binding energy.

How radioactive substances undergo fusion to reach more stable states.

### Mass-Energy Equivalence

Mass-energy equivalence states that mass is concentrated energy. In his theory of special relativity Einstein formulated the equation E = mc2. There is a tremendous amount of energy in mass. A 20g marble contains as much energy as a 500 kiloton hydrogen bomb, but this energy is very difficult to release. It can be released through matter-antimatter annihilation, when matter and antimatter come together. Nuclear reactions can be understood to release so much more energy than chemical reactions because of the mass changes.

An explanation of mass energy equivalence.

A brief introduction to mass-energy equivalence (E = mc2)
Recognize the fundamental source of all energy in the universe as the conversion of mass into energy.
Understand the use of mass-equivalence equation.

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