NUCLEAR WEAPONS
Paul Sneller
History
1905 – Einstein’s Theory of Special Relativity.
1932 – The Neutron is Discovered by James Chadwick.
1938 – Otto Hahn and Fritz Strassman are able to split a
uranium atom by bombarding it with neutrons.
1942 – First self sustaining nuclear reaction is produced by
scientists at the University of Chicago.
1945 – First Nuclear Weapon detonated at Trinity, New
Mexico.
1945 – Nuclear Weapons are dropped on the cities of
Hiroshima and Nagasaki.
1952 – First Teller-Ulam hydrogen bomb detonated.
Nuclear Fission
A nuclear reaction in which an atomic nucleus splits into
fragments.
Fission occurs readily in U-235 and Pu-239 when bombarded
with neutrons.
The sum of the product masses is less than the mass of the
original atom.
The lost mass is converted directly into energy.
The fission of a single Uranium-235 nucleus generates about
3.36E-11J
Nuclear Fusion
The combination of two nuclei to form a single atom.
The product’s mass is less than the mass of the original
atoms.
Fusion occurs most readily in a combination of the hydrogen
isotopes deuterium and tritium.
Temperature in the millions of degrees is required to initiate
fusion.
A Deuterium-Tritium fusion generates about 2.8E-12J of
energy
Criticality
In order for a nuclear reaction to be self-sustaining, there
must be a “critical mass” of fissile material.
This is the mass necessary so that, on average, at least one
neutron produced by every fission goes on to trigger another
fission.
Having less than critical mass will cause the bomb to “fizzle”
and have a very low efficiency.
Actual mass required for criticality depends on the density of
the mass, the shape of its configuration, and the
presence/effectiveness of the neutron reflector.
Due to natural emission of neutrons, any critical mass has a
chance of beginning a nuclear chain reaction.
The Fission Bomb
To prevent premature detonation of a weapon, the nuclear
material must be separated into two or more sub critical
masses.
The mechanism which combines these masses is the most
important part of the weapon.
The mechanism must combine the sub critical masses into
one supercritical mass fast enough that the mass is fully
assembled before there is any chance of the chain reaction
blowing the fissile material apart and causing the bomb to
fizzle.
The Neutron Generator
In order to ensure that a chain reaction begins, there has to
be free neutrons present in the fissile material when the
critical mass is assembled.
A combination of Po-210 which emits alpha particles, and
Beryllium, which emits neutrons when struck by an alpha
particle.
The two substances can be separated by a foil which blocks
alpha particles and is designed to break when the bomb is
triggered.
The Tamper
The tamper is a thick layer of heavy material which is
designed to produce pressure on the fissionable core as the
bomb detonates, allowing more fissions to occur before the
materials are blown apart by the energy release.
The tamper is usually constructed out of U-238 and doubles
as a neutron reflector, redirecting neutrons back into the core
and increasing the efficiency of the reaction.
The most effective tamper is Be-9 which actually produces
two neutrons when struck by a single neutron.
Weapon Designs
Gun-triggered fission
Implosion-triggered fission
Fusion Bombs
Gun-triggered
This is the simplest form of nuclear weapon.
A bullet of U-235 is propelled by explosives into a U-235
sphere.
Because of the relatively slow combination of the critical
mass, this method works only with U-235.
This is the type of bomb that destroyed the Japanese city of
Hiroshima.
Gun-triggered
Implosion-triggered
A sub critical sphere of plutonium is surrounded by
explosives, when the explosives detonate they create a
shockwave which compresses the core.
The increased density of the core causes it to become
supercritical, and the nuclear reaction begins.
This method can be used with both U-235 and Pu-239.
This is the type of weapon detonated at the Trinity site, and
on the Japanese city of Nagasaki.
To properly compress instead of blowing it apart, it is
necessary to use explosive lenses, which create a concave
shockwave that fits the surface of the core.
Implosion Triggered
Teller-Ulam Bomb
The first true fusion bomb design.
Utilizes a fission weapon to provide the necessary energy to
cause fusion.
The massive amount of X-rays released by the fission, which
travel much faster than the actual explosion, are contained by
a thick tamper and used to provide the heat to initiate a
fusion reaction before the explosion has a chance to blow
apart the bomb.
Uses lithium deuterate as a fuel.
When lithium is struck by a neutron it produces an alpha
particle and tritium, which readily fuses with the deuterium in
the extreme temperature created by the fission bomb.
Can be scaled to nearly limitless power.
Teller-Ulam Bomb
Teller-Ulam Bomb
The Effects
Standard Nuclear weapons emit approximately 50% of their
total energy as blast energy, 35% as thermal energy, and
15% as radiation.
The actual effects of the weapon vary greatly depending on
the yield, and the detonation point.
Detonation in the upper atmosphere can create massive
EMPs, severely damaging many electronics.
Detonation in the lower atmosphere results in enormous
pressure damage over a larger area.
Surface Detonation results in blast and thermal damage, and
large amounts of fallout.
Subterranean detonation results in large shockwaves, but
minimizes most of the effects, provided the blast does not
break the surface
10 Kiloton Surface Blast
1/3 mile radius: All but the sturdiest of buildings are
completely destroyed, those that remain are merely empty
shells, fatality rate is nearly 100%
3/4 mile radius: Anyone directly exposed to the blast receives
a lethal radiation dose, all buildings suffer heavy damages,
fatality rate is approximately 50% with 45% injured.
1 mile radius: Heat wave causes widespread fires and the
area is ravaged by radiation. Approximately 5% of the
population is killed, with 45% injured.
25 Megaton Airburst
6.5 mile radius: All but the sturdiest of buildings are
destroyed, fatality rate is nearly 100%
10.7 mile radius: Buildings suffer heavy damage,
approximately 50% of the population is dead and 45%
injured.
20 mile radius: Windows, and many of the occupants of large
buildings are blown out, small buildings are heavily damaged
or destroyed, approximately 5% dead and 45% injured.
30.4 mile radius: Buildings are slightly damaged,
approximately 25% of the population is injured.
Construction Feasibility
To produce a functional gun-triggered nuclear weapon, there
are only 4 main requirements.
Access to a sufficient quantity of weapons grade material, or
the equipment needed to enrich uranium ore.
Precision machine tools.
Safety equipment to protect against radiation.
High explosives.
Construction Feasibility
Due to the widespread availability of resources such as
explosives, machine tools, and protective gear, sufficient
monetary resources make such items trivial.
The only real impediment to non-nuclear nations and
terrorists is the availability of weapons grade Uranium.
Uranium Acquisition
Although Uranium is actually fairly common in nature,
Uranium-235, the isotope required for nuclear weapons,
accounts for only .71% of all naturally occurring Uranium.
Any sizable amount of Uranium-235 is closely monitored by
international agencies, therefore the most feasible means of
obtaining weapons grade uranium is to enrich uranium ore.
Uranium Enrichment
There are several methods to enriching Uranium
The most efficient method is by combining uranium with
fluorine to Uranium hexafluoride and then using a gas
centrifuge to separate the isotopes.
Other methods include electromagnetic isotope separation
(EMIS) and gaseous diffusion.
All of these methods require a significant amount of
electricity, some specialized equipment, a larger supply of
uranium ore, and a good deal of time, as each process only
slightly increases the percentage of U-235, and concentrations
of over 90% are necessary for nuclear weapons.
Conclusion
Nuclear weapons are one of modern science’s greatest
achievements, harnessing the conversion of mass to energy.
They range from fairly simple, to extremely complex, but they
all are extremely powerful and deadly.
Although construction of a basic nuclear weapon is fairly
straightforward, the logistical problems involved with
obtaining sufficient nuclear fuel, the careful monitoring of
nuclear development should prevent terrorists and third world
nations from constructing them for quite some time.