1 Case Study: Nuclear Weapons
Case Study: Nuclear Weapons
A nuclear weapon is commonly defined as a device, which uses a nuclear reaction
for destructive means.
Contents:
1. Introduction
2. Basic Nuclear Chemistry Definitions and Concepts
3. Example of Fusion Reaction
4. Nuclear Weaponry
5. Outside links
6. References
7. Outside Links
8. Problems
Introduction
The first nuclear weapon was successfully detonated on July 16, 1945. The nuclear
weapon, code named “Trinity”, yielded an explosion which was equivalent to 20
kilotons of Trinitrotoluene (TNT). This reaction unexpectedly had a shock wave
which could be felt 100 miles away. Compared to chemical reactions, the amount of
energy that can be released from nuclear reactions can be up to a million times
greater. Before we can fully understand the chemical complexity and appreciate the
engineering elegance of a nuclear weapon, it is important to grasp basic nuclear
chemistry concepts.
Basic Nuclear Chemistry Definitions and Concepts
Nuclear Fission- This type of nuclear reaction is caused by nuclear decay of an
unstable atom that has been hit by a neutron. As a result of the instability of the
atom, the nucleus splits into 2 fission fragments also yielding free neutrons and
exorbitant amounts of energy (both in the form of electromagnetic radiation and
kinetic energy). A neutron carries no electric charge but the nucleus of an atom
does - a positive charge. Like with magnets, like charges repel each other, so
particles that carry positive electric charges like alpha particles are repelled by the
nucleus of an atom and thus do not stick to the nucleus. However, a neutrally
charged neutron can combine with the nucleus of an atom which then causes the
nucleus to become unstable and split into 2 nuclei. According to Einstein's formula,
E=mc2, energy is released from this reaction along with other neutrons that have
the same effect on nearby nuclei and a chain reaction occurs which yields an
incredible amount of energy.
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Figure 1: Picture of the Fission reaction of Uranium-236 producing fission
fragments, neutrons and 3.20X1011 Joules of energy. Provided by
"Wikipedia".
Nuclear Fusion- Fusion is almost completely complimentary to fission. It is the
process in which a nuclear reaction where two nuclei are joined together to form a
heavier nucleus. The reaction also yields free neutrons and exorbitant amounts of
energy from binding energy. Our sun is a "nuclear furnace" in the sense that it is a
place where nuclear fusion occurs. Although a nuclear fusion reactor would
undoubtedly be better for our environment, such reactions are not yet possible
because no known material can withstand the incredible high temperatures needed
for such reactions to occur.
Figure 2: An example of nuclear fusion in which deuterium and tritium fuse
together to form helium-4 and freeing a neutron. Provided by "Wikipedia".
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Example of Fusion Reaction
2
D+3T →
4
2He
+10N + 17.6 MeV
Fissile / Fissionable – An atom is fissionable if it is capable of undergoing fission.
If an atom is Fissile it is not only able to undergo fission, but it is also capable of
sustaining a nuclear chain reaction.
Nuclear Chain Reaction- As stated earlier in the text, a nuclear fission reaction
yields free neutrons. In a nuclear chain reaction, the free neutrons from a nuclear
fission reaction bombard nearby Fissile isotopes resulting in multiple fission
reactions. These reactions result in colossal amounts of kinetic energy and gamma
radiation.
Critical Mass- The amount of fissile isotope required to successfully assist a nuclear
chain reaction. If the fissile material is at a subcritical mass it cannot sustain a
nuclear chain reaction. On the other hand, if the fissile material is at a supercritical
mass, it will undergo a chain reaction at a faster rate.
Nuclear Weaponry
A nuclear weapon can either undergo a nuclear fission reaction (atomic bomb) or a
nuclear fusion reaction (H bomb or thermonuclear bomb).
Weapons Utilizing Fission Reactions
The first nuclear weapons built underwent pure nuclear fission. Uranium-235 and
Plutonium-239 were the most common fissile isotopes used. (Uranium-235 is less
than 1% naturally abundant. It requires complex methods of enrichment to be a
fissile isotope). There are 2 basic nuclear fission weapon designs:
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Gun assembly- An uranium-235 bullet is fired through a barrel at a fissile
Uranium-235 target. The collision of the two isotopes initiates a chain reaction.
The gun assembly design only proves practical with the uranium-235 isotope.
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Implosion- A critical mass of a fissile material (U-235 or Pu-239) is surrounded
by highly explosive material. When detonated, the high explosives compress the
fissile material causing it to assume a state of supercritical mass. The
supercritical mass instantaneously begins to undergo a chain reaction.
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Figure 3. Gun and implosion design for fission bombs. Image courtesy of
Wikipedia
Weapons Utilizing Fusion Reactions
The first nuclear fusion weapons (also known as thermonuclear weapons) were
designed to initiate a fission-based chain reaction. The fusion reaction between
tritium and deuterium would result in the free neutrons necessary to bombard a
fissile isotope and start a nuclear chain reaction. The first thermonuclear weapon
was detonated in November of 1952. Similar to the nuclear implosion design,
thermonuclear weapons use the heat and radiation from a fission reaction to make
the fissile material assume a state of supercritical mass. The supercritical mass then
instantaneously undergoes a fusion chain reaction yielding exponentially more
energy than a fission chain reaction.
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Figure 4. Fission bomb design. Image courtesy of Wikipedia
Outside links
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http://www.youtube.com/watch?v=fWoND...eature=related (real footage of little
boy nuclear weapon dropped on Hiroshima. The fission nuclear weapon used the
"Gun Assembly" design)
http://www.youtube.com/watch?v=FfoQsZa8F1c (The tzar bomb was the largest
nuclear weapon ever detonated. Using a fusion chain reaction, the bomb yielded
energy compared to 50 megatons of TNT)
http://www.youtube.com/watch?v=52pARFOTuVU (The first Nuclear detonation
of Trinity)
http://www.youtube.com/watch?v=m61jd0YrNy8 (Detailed animations of the
mechanisms of both types of fission reactions (gun assembly and implosion).
References
1. Miller, Richard L. Under the Cloud : The Decades of Nuclear Testing. New York:
Free P, 1999.
2. Petrucci, Ralph H., William S. Harwood, and Geoff E. Herring. General Chemistry
: Principles and Modern Applications. Upper Saddle River: Prentice Hall PTR,
2006. 1041-065.
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Outside Links
http://en.wikipedia.org/wiki/Uranium-235
http://en.wikipedia.org/wiki/Nuclear_fusion
http://en.wikipedia.org/wiki/Nuclear_chain_reaction
http://en.wikipedia.org/wiki/Nuclear_weapon
http://en.wikipedia.org/wiki/Nuclear_weapon_design
http://en.wikipedia.org/wiki/Critical_mass
http://www.atomicarchive.com/History/mp/index.shtml
http://en.wikipedia.org/wiki/Nuclear_fission
http://enviro.org.au/news-Sep20055.asp
http://www.nucleardarkness.org/nuclear/effectsofnuclearweapons/
http://www.fas.org/nuke/intro/nuke/effects.htm
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Problems
1. Given the following nuclear fusion reaction, what particle corresponds to x?
21H+21H -->X+energy
a)
4
2He
b)17587Fr
c)
14
6C
d)0-1e
e)none of the above
2. Which of the following best describes a Nuclear Fusion Reaction?
a) A nuclear reaction in which 2 small nuclei combine to form one large nucleus.
b) A reaction in which a large nucleaus splits into two smaller and fast moving
particles.
c) The combination of a nucleus and an electron.
d) The combination of a nucleus and a positron.
e) The combination of a nucleus and an alpha particle?
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3. Which of the folowing bect describes a Nuclear Fission Reaction?
a) A nuclear reaction in which 2 small nuclei combine to form one large nucleus.
4. The following nuclear reaction is carried out with the corresponding masses of
the reactants:
3
1H
7.556g
+
1
1
H
yields
2.143g
4
2
He + Energy
Xg
If 4.56 X1011 Joules of energy was released, what mass in grams of
produced?
4
2
He is
b) A reaction in which a large nucleus splits into two smaller and fast moving
particles.
c) The combination of a nucleus and an electron.
d) The combination of a nucleus and a positron.