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There are 2 types of atomic explosions that can be facilitated by
U-235; fission and fusion. Fission, simply put, is a nuclear reaction in
which an atomic nucleus splits into fragments, usually two fragments
of comparable mass, with the evolution of approximately 100 million to
several hundred million volts of energy. This energy is expelled
explosively and violently in the atomic bomb. A fusion reaction is
invariably started with a fission reaction, but unlike the fission
reaction, the fusion (Hydrogen) bomb derives its power from the fusing
of nuclei of various hydrogen isotopes in the formation of helium
nuclei. Being that the bomb in this file is strictly atomic, the other
aspects of the Hydrogen Bomb will be set aside for now.
The massive power behind the reaction in an atomic bomb arises from
the forces that hold the atom together. These forces are akin to, but
not quite the same as, magnetism.
Atoms are comprised of three sub-atomic particles. Protons and
neutrons cluster together to form the nucleus (central mass) of the
atom while the electrons orbit the nucleus much like planets around a
sun. It is these particles that determine the stability of the atom.
Most natural elements have very stable atoms which are impossible to
split except by bombardment by particle accelerators. For all practical
purposes, the one true element whose atoms can be split
comparatively easily is the metal Uranium. Uranium\'s atoms are
unusually large, henceforth, it is hard for them to hold together firmly.
This makes Uranium-235 an exceptional candidate for nuclear fission.
Uranium is a heavy metal, heavier than gold, and not only does it have
the largest atoms of any natural element, the atoms that comprise
Uranium have far more neutrons than protons. This does not enhance
their capacity to split, but it does have an important bearing on their
capacity to facilitate an explosion.
There are two isotopes of Uranium. Natural Uranium consists mostly
of isotope U-238, which has 92 protons and 146 neutrons
(92+146=238). Mixed with this isotope, one will find a 0.6%
accumulation of U-235, which has only 143 neutrons. This isotope,
unlike U-238, has atoms that can be split, thus it is termed
"fissionable" and useful in making atomic bombs. Being that U-238 is
neutron-heavy, it reflects neutrons, rather than absorbing them like its
brother isotope, U-235. (U-238 serves no function in an atomic
reaction, but its properties provide an excellent shield for the U-235 in
a constructed bomb as a neutron reflector. This helps prevent an
accidental chain reaction between the larger U-235 mass and its
\'bullet\' counterpart within the bomb. Also note that while U-238 cannot
facilitate a chain-reaction, it can be neutron-saturated to produce
Plutonium (Pu-239). Plutonium is fissionable and can be used in place
of Uranium-235 albeit, with a different model of detonator} in an
Both isotopes of Uranium are naturally radioactive. Their bulky atoms
disintegrate over a period of time. Given enough time, (over 100,000
years or more) Uranium will eventually lose so many particles that it
will turn into the metal lead. However, this process can be
accelerated. This process is known as the chain reaction. Instead of
disintegrating slowly, the atoms are forcibly split by neutrons forcing
their way into the nucleus. A U-235 atom is so unstable that a blow
from a single neutron is enough to split it and henceforth bring on a
chain reaction. This can happen even when a critical mass is present.
When this chain reaction occurs, the Uranium atom splits into two
smaller atoms of different elements, such as Barium and Krypton.
When a U-235 atom splits, it gives off energy in the form of heat and
Gamma radiation, which is the most powerful form of radioactivity and
the most lethal. When this reaction occurs, the split atom will also
give off two or three of its \'spare\' neutrons, which are not needed to
make either Barium or Krypton. These spare neutrons fly out with
sufficient force to split other atoms they come in contact with. [See
chart below] In theory, it is necessary to split only one U-235 atom,
and the neutrons from this will split other atoms, which will split
more...so on and so forth. This progression does not take place
arithmetically, but geometrically. All of this will happen within a
millionth of a second.
The minimum amount to start a chain reaction as described above is
known as SuperCritical Mass. The actual mass needed to facilitate
this chain reaction depends upon the purity of the material, but for
pure U-235, it is 110 pounds (50 kilograms), but Uranium is never
quite pure, so in reality
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Nuclear physics, Physics, Nature, Radioactivity, Actinides, Nuclear chemistry, Nuclear technology, Nuclear fission, Neutron, Uranium, Plutonium, Isotope
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