Inventors
Nuclear
Fission/Nuclear Fusion
Part One: The
History of the Atomic Bomb
Fission (A-Bomb) &
Fusion (H-Bomb)
There are two 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, emitting 100 million to several
hundred million volts of energy. This energy is expelled explosively and
violently in the atomic bomb. A fusion reaction is usually started with
a fission reaction, but unlike the fission (atomic) bomb, the fusion (hydrogen)
bomb derives its power from the fusing of nuclei of various hydrogen isotopes
into helium nuclei. This article discusses the A-bomb or atomic bomb.
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 various numbers
and combinations of the three sub-atomic particles: protons, neutrons and
electrons. 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 the balance and arrangement of these particles that
determine the stability of the atom.
Most elements have very stable atoms
which are impossible to split except by bombardment in particle accelerators.
For all practical purposes, the only natural element whose atoms can be
split easily is uranium, a heavy metal with the largest atom of all natural
elements and an unusually high neutron-to-proton ratio. This higher ratio
does not enhance its "splitability," but it does have an important bearing
on its ability to facilitate an explosion, making uranium-235 an exceptional
candidate for nuclear fission.
There are two naturally-occurring
isotopes of uranium. Natural uranium consists mostly of isotope U-238,
with 92 protons and 146 neutrons (92+146=238) per atom. Mixed with this
is a 0.6% accumulation of U-235, with only 143 neutrons per atom. The atoms
of this lighter isotope can be split, thus it is "fissionable" and useful
in making atomic bombs. Neutron-heavy U-238 has a role to play in the atomic
bomb as well since its neutron-heavy atoms can deflect stray neutrons,
preventing an accidental chain reaction in a uranium bomb and keeping neutrons
contained in a plutonium bomb. [U-238 can also be "saturated" to produce
plutonium (Pu-239), a man-made, radioactive element also used in atomic
bombs.]
Both isotopes of uranium are naturally
radioactive; their bulky atoms disintegrating over time. Given enough time
(hundreds of thousands of years) uranium will eventually lose so many particles
that it will turn into lead. This process of decay can be greatly accelerated
in what is known as a chain reaction. Instead of disintegrating naturally
and slowly, the atoms are forcibly split by bombardment with neutrons.
A blow from a single neutron is enough
to split the less-stable U-235 atom, creating atoms of smaller elements
(often barium and krypton) and releasing heat and gamma radiation (the
most powerful and lethal form of radioactivity). The chain reaction occurs
when "spare" neutrons from this atom fly out with sufficient force to split
other U-235 atoms they come in contact with. In theory, it is necessary
to split only one U-235 atom, which will release neutrons which will split
other atoms, which will release neutrons ... and so on. This progression
is not arithmetic; it is geometric and takes place within a millionth of
a second.
The minimum amount to start a chain
reaction as described above is known as super critical mass. For pure U-235,
it is 110 pounds (50 kilograms). No uranium is ever quite pure, however,
so in reality more will be needed.
U-235, U-238 and Plutonium
Uranium is not the only material
used for making atomic bombs. Another material is the Pu-239 isotope of
the man-made element plutonium. Plutonium is only found naturally in minute
traces, so useable amounts must be produced from uranium. In a nuclear
reactor, uranium's heavier U-238 isotope can be forced to acquire extra
particles, eventually becoming the plutonium.
Plutonium will not start a fast chain
reaction by itself, but this difficulty is overcome by having a neutron
source, a highly radioactive material that gives off neutrons faster than
the Plutonium itself. In certain types of bombs, a mixture of the elements
Beryllium and Polonium is used to bring about this reaction. Only a small
piece is needed (super critical mass is about 32 pounds, though as little
as 22 can be used). The material is not fissionable in and of itself, but
merely acts as a catalyst to the greater reaction.
Related Links
Nuclear
Innovations
More detailed information on different
nuclear inventions and the history of nuclear physics. Timeline of nuclear
technology and major figures in radiation history.
Albert
Einstein
German-American physicist who developed
the special and general theories of relativity - the irony for this idealistic
man was that his famous postulation of an energy-mass equation, which states
that a particle of matter can be converted into an enormous quantity of
energy, had its spectacular proof in the creation of the atomic and hydrogen
bombs, the most destructive weapons ever known.
Plutonium
on the Internet
information
for parts of this article was taken from public domain material released
by Outlaw Labs
Important disclaimer information about this About site.
|