Nuclear Fission

1
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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Section 24-3
Nuclear Fission

• Nuclear power plants use fission to produce
  electricity by striking uranium-235 with neutrons.

3
Section 24-3
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.
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  udent_view0/chapter24/concepts_in_motion.html

4
Section 24-3
Nuclear Fission (cont.)
5
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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Section 24-3
Nuclear Fission (cont.)
http//www.youtube.com/watch?vqybUFnY7Y8w
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Section 24-3
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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Section 24-3
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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Section 24-3
Nuclear Reactors (cont.)
10
Section 24-3
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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Section 24-3
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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Section 24-3
Nuclear Fusion (cont.)

• Fusion reactions are also known as thermonuclear
  reactions.

• Many problems must be solved before nuclear
  fusion is a practical energy source.

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Section 24-3
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

1. A
2. B
3. C
4. D

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Section 24-3
Section 24.3 Assessment
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

1. A
2. B
3. C
4. D