Section 24-3
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Transcript of Section 24-3
Section 24-3
Nuclear Fission
• Stability of elements is best around a mass number of 60.
• Atoms with a mass number greater than 60 tend to gain stability by fragmenting.
• The splitting of nuclei into fragments is known as nuclear fission.
• Fission is accompanied with a very large release of energy.
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Nuclear Fission
• Nuclear power plants use fission to produce electricity by striking uranium-235 with neutrons.
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Nuclear Fission (cont.)
• Each fission of U-235 releases three additional neutrons.
• Each of those neutrons can release three more neutrons.
• The self-sustaining process is called a chain reaction.
• http://glencoe.mcgraw-hill.com/sites/007874637x/student_view0/chapter24/concepts_in_motion.html
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Nuclear Fission (cont.)
Section 24-3
Nuclear Fission (cont.)
• There must be sufficient mass to get the chain reaction started. If not the neutrons escape before striking other nuclei.
• Without sufficient mass, neutrons escape from the sample before starting a chain reaction.
• Samples with enough mass to sustain a chain reaction are said to have critical mass.
• Samples with mass that is much greater than the critical mass have a reaction that escalates at a violent level and can cause a nuclear explosion. This is the supercritical mass.
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Nuclear Fission (cont.)
http://www.youtube.com/watch?v=qybUFnY7Y8w
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Nuclear Reactors
• Nuclear fission produces the energy generated by nuclear reactors.
• The fission within a reactor is started by a neutron-emitting source and is stopped by positioning the control rods to absorb virtually all of the neutrons produced in the reaction.
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Nuclear Reactors (cont.)
• The reactor core contains a reflector that reflects neutrons back into the core, where they react with fuel rods.
• Nuclear reactors produce highly radioactive nuclear waste.
• Breeder reactors produce more fuel than they consume.
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Nuclear Reactors (cont.)
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Nuclear Fusion
• It is possible to bind together two or more lighter elements (mass number less than 60).
• The combining of atomic nuclei is called nuclear fusion.
• Nuclear fusion is capable of releasing very large amounts of energy.
• The sun is powered by the fusion of hydrogen atoms to form helium atoms and a lot of energy.
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Nuclear Fusion (cont.)
• Fusion has several advantages over fission.
− Lightweight isotopes are abundant.
− Fusion products are not radioactive.
− However, fusion requires extremely high energies to initiate and sustain a reaction.
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Nuclear Fusion (cont.)
• Fusion reactions are also known as thermonuclear reactions.
• Many problems must be solved before nuclear fusion is a practical energy source.
A. A
B. B
C. C
D. D
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A B C D
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Section 24.3 Assessment
Bombarding a nuclei with charged particle in order to create new elements is called ____.
A. nuclear conversion
B. nuclear decay
C. induced decay
D. induced transmutation
A. A
B. B
C. C
D. D
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Section 24.3 Assessment
A B C D
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Thermonuclear reactions involve:
A. splitting nuclei into smaller fragments
B. fusing nuclei together to form larger particles
C. bombarding nuclei with charged particles
D. generating electricity in a nuclear reactor