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Nuclear Fission Versus Nuclear Fusion
Different Processes
That Yield Different Products
by Anne Marie Helmenstine, Ph.D.
Nuclear fission and nuclear fusion both are
nuclear phenomena that release large amounts of energy, but they are
different processes which yield different products.
Learn what nuclear fission and nuclear fusion are and how
you can tell them apart.
Nuclear Fission
Nuclear fission takes place when an atom's nucleus
splits into two or more smaller nuclei. These smaller nuclei are called fission
products.
Particles (e.g., neutrons, photons, alpha particles)
usually are released, too. This is an exothermic
process releasing the kinetic energy of the fission products and energy in
the form of gamma radiation.
The reason energy is released is because the fission
products are more stable (less energetic) than the parent nucleus.
Fission may be considered a form of element transmutation
since changing the number of protons of an element essentially changes the
element from one into another.
Nuclear fission may occur naturally, as in the decay of
radioactive isotopes, or it can be forced to occur in a reactor or weapon.
Nuclear Fission Example
23592U + 10n → 9038Sr + 14354Xe + 310n
Nuclear Fusion
Nuclear fusion is a process in which atomic
nuclei are fused together to form heavier nuclei.
Extremely high temperatures (on the order of 1.5 x 107°C) can force
nuclei together so the strong nuclear force can bond them.
Large amounts of energy are released when fusion occurs. It
may seem counterintuitive that energy is released both when atoms split and
when they merge.
The reason energy is released from fusion is because the
two atoms have more energy than a single atom.
A lot of energy is required to force protons close enough
together to overcome the repulsion between them, but at some point, the strong
force that binds them overcomes the electrical repulsion.
When the nuclei are merged, the excess energy is released.
Like fission, nuclear fusion can also transmute one element
into another. For example, hydrogen nuclei fuse in stars to form the element
helium.
Fusion is also used to force together atomic nuclei to form
the newest elements on the periodic table.
While fusion occurs in nature, it's in stars, not on Earth.
Fusion on Earth only occurs in labs and weapons.
Nuclear Fusion Examples
The reactions which take place in the sun provide an example
of nuclear fusion:
11H + 21H → 32He
32He + 32He → 42He + 211H
11H + 11H → 21H + 0+1β
Distinguishing Between
Fission and Fusion
Both fission and fusion release enormous amounts of energy.
Both fission and fusion reactions can occur in nuclear bombs.
So, how can you tell fission and fusion apart?
· Fission breaks atomic nuclei
into smaller pieces. The starting elements have a higher atomic number than
that of the fission products. For example, uranium can fission to yield
strontium and krypton.
· Fusion joins atomic nuclei
together. The element formed has more neutrons or more protons than that of the
starting material. For example, hydrogen and hydrogen can fuse to form helium.
· Fission occurs naturally on Earth. An example
is the spontaneous fission of uranium, which only happens if enough
uranium is present in a small enough volume (rarely). Fusion, on the other
hand, does not occur naturally on Earth. Fusion occurs in stars.
Anne Marie Helmenstine, Ph.D.
· Ph.D.
in biomedical sciences from the University of Tennessee at Knoxville - Oak
Ridge National Laboratory.
· Science
educator with experience teaching chemistry, biology, astronomy, and
physics at the high school, college, and graduate levels.
· ThoughtCo
and About Education chemistry expert since 2001.
· Widely-published
graphic artist, responsible for printable periodic tables and other
illustrations used in science.
Experience
Anne Helmenstine, Ph.D. has covered
chemistry for ThoughtCo and About Education since 2001, and other sciences
since 2013. She taught chemistry, biology, astronomy, and physics at the high
school, college, and graduate levels. She has worked as a research
scientist and also abstracting and indexing diverse scientific literature for
the Department of Energy.
In addition to her work as a science writer, Dr.
Helmenstine currently serves as a scientific consultant, specializing in
problems requiring an interdisciplinary approach. Previously, she worked
as a research scientist and college professor.
Education
Dr. Helmenstine holds a Ph.D. in biomedical
sciences from the University of Tennessee at Knoxville and a B.A.
in physics and mathematics with a minor in chemistry from Hastings
College. In her doctoral work, Dr. Helmenstine developed ultra-sensitive
chemical detection and medical diagnostic tests.
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publication.https://www.thoughtco.com/nuclear-fission-versus-nuclear-fusion-608645
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