Unit 8 Section 2: Nuclear Reactions

An Introduction to Nuclear Fission and Fusion

Objectives:

• Explain that nuclear reactions deal with interactions between the nuclei of atoms and chemical reactions occur when electrons interact.

• Describe the relationship between matter and energy.

• Explain and differentiate between nuclear fission and nuclear fusion.

• Understand that both fission and fusion processes deal with matter and energy.

Nuclear Energy vs. Chemical Energy

• What is the difference between nuclear and chemical energy?• Chemical Energy: Energy that is released

during chemical reactions. Chemical energy involves electrons.

• Nuclear Energy: Energy that is released from the atomic nucleus. This involves much larger energies than chemical reactions.

Matter and Energy

• Recall the law of conservation of energy: • Energy cannot be

created or destroyed.

• New concept:• Matter and energy

are 2 forms of the same thing

Einstein’s Famous Equation:E = mc2

• Matter can be changed into Energy• Einstein’s formula tell us how the change

occurs• In E = mc2,

• E = Energy• m = Mass• c = Speed of Light (Universal Constant)

E = mc2

• The equation can be read as follows:• Energy (E) is equal to Mass (m) multiplied

by the Speed of Light (c) squared

• This tells us that a small amount of mass can be converted into a very large amount of energy because the speed of light (c) is an extremely large number

• c = 3.0 x 108 m/s

Fission: What is it?

• Fission:• The process of

splitting an atomic nucleus into fission fragments.

• Fission fragments(products):• In the form of smaller

atomic nuclei and neutrons

• Releases radiation

Fission (cont’d)

• LARGE amounts of energy are produced by the fission process

• Fission involves heavy atoms with a lot of protons and neutrons (nucleons)

• How and why does fission happen?• How: the nuclei of the heavy atoms are hit by

neutrons; this starts the fission process.• Why: fission occurs because of the electrostatic

repulsion created by large numbers of protons within the nuclei of heavy atoms.

Example of Fission Reaction

• Start with:• U-235 + 1 neutron

• Product: • 2 neutrons + Kr-92

+ Ba-142 + Energy

Explanation of Fission Reaction

• Explanation: • A neutron hits an atom of U-235. • It absorbs the neutron and becomes U-236

which is unstable. • Fission occurs and more neutrons are

released in the reaction. • The stray neutrons strike other U-235

atoms to start a nuclear chain reaction.

The Fission Process

Fission (cont’d)

• The fission process is NATURAL• There was a natural

uranium reactor in West Africa over 2 billion years ago.

• Why is fission useful?• It generates a large

amount of energy and this heat can be captured by nuclear power plants to produce electricity.

What elements are good for fission?

• Uranium 235 (U-235)• Uranium 238 (U-238)• Elements with an

atomic number higher than 92 do not exist in nature; they are also good for the fission process.

Fusion: What is it?

• Fusion:• A nuclear reaction in which two light nuclei

combine or fuse to make a larger, heavier nucleus.

• This process generates LOTS of energy (Remember E = mc2).

• In order for fusion to begin, a large amount of energy is needed to overcome the electrical charges of the nuclei and fuse them together.

Fusion Facts

• Fusion reactions DO NOT occur naturally on our planet, but nuclear fusion is what powers the stars.• The sun fuses

hydrogen atoms to produce helium, subatomic particles, and a large amount of energy.

Diagram of Nuclear Fusion

Review

• Mass and energy are two forms of the same thing; neither can be created or destroyed, but mass can be converted into energy (E = mc2).

• Fission is a nuclear reaction in which:• A heavy atomic nucleus is split into lighter atomic

nuclei.

• Fusion is a nuclear reaction in which:• 2 light nuclei are combined into a single, heavier

atomic nucleus.

Quiz Question #1

• Which nuclear process produces large amounts of energy?

A. Fission

B. Fusion

C. Both fission and fusion

D. Neither fission or fusion

Quiz Question #1

• Which nuclear process produces large amounts of energy?

A. Fission

B. Fusion

C. Both fission and fusion

D. Neither fission or fusion

Quiz Question #2

• Fission is the process that __________ atomic nuclei.

A. combines

B. burns up

C. stores

D. splits

Quiz Question #2

• Fission is the process that __________ atomic nuclei.

A. combines

B. burns up

C. stores

D. splits

Quiz Question #3

• Mass may be converted into energy.

A. True

B. False

Quiz Question #3

• Mass may be converted into energy.

A. True

B. False

Quiz Question #4

• The fission process requires heavy atomic nuclei.

A. True

B. False

Quiz Question #4

• The fission process requires heavy atomic nuclei.

A. True

B. False

Quiz Question #5

• Name the nuclear reaction that occurs within the sun.

Quiz Question #5

• Name the nuclear reaction that occurs within the sun. • Nuclear Fusion

Quiz Question #6

• Fission is a natural process that occurs on the planet earth.

A. True

B. False

Quiz Question #6

• Fission is a natural process that occurs on the planet earth.

A. True

B. False

Quiz Question #7

• Explain this equation:• E = mc2

Quiz Question #7

• Explain this equation:• E = mc2

• Energy is equal to mass times the speed of light squared.

https://www.youtube.com/watch?v=KWAsz59F8gA