unit 8 section 2: nuclear reactions an introduction to nuclear fission and fusion
TRANSCRIPT
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.
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.
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 #7
• Explain this equation:• E = mc2
• Energy is equal to mass times the speed of light squared.