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.

Section 24-3

Nuclear Fission

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

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.

• http://glencoe.mcgraw-hill.com/sites/007874637x/student_view0/chapter24/concepts_in_motion.html

Section 24-3

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.

Section 24-3

Nuclear Fission (cont.)

http://www.youtube.com/watch?v=qybUFnY7Y8w

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.

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.

Section 24-3

Nuclear Reactors (cont.)

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.

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.

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.

A. A

B. B

C. C

D. D

Section 24-3

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

Section 24-3

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