How Do They Work?
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answer to the above question.
Little Boy Fission Bomb dropped on
When the sub-atomic particles of an atom break apart they do so with
great speed. Much of this speed (or Kinetic energy) is converted to
heat. This heat can be harnessed and used in nuclear weapons.
make this energy available it is necessary to start a chain
reaction. A chain reaction occurs when the sub-atomic particles from
one atom smashes into another atom causing this to break apart and
nuclear weapon all the energy that is created by a chain reaction is
released almost instantaneously, which creates a tremendous,
Naturally occurring atoms do not explode in chain reactions. This is
because they do not contain enough fissile atoms to sustain a chain
reaction To create suitable atoms for the process to occur enriching
must take place.
Naturally occurring uranium 235 contains around 7 fissile atoms per
thousand. This is not enough to sustain a chain reaction.
Enriched nuclear fuel contains more fissile atoms, thus they are
better at sustaining a chain reaction. To enrich uranium, scientists
add plutonium to it.
Fission creates energy by breaking apart atoms.
Fusion works in the opposite way. It creates energy by joining
Although atomic bombs which work by fission are devastating weapons
(both the bombs dropped on Japan by America towards the end of WWII
were fission bombs) fusion weapons (or thermonuclear weapons – to
give them they proper name) are far more efficient. For example when
1 kg of uranium is converted into heat energy by fission it produces
6 times less energy than when 1kg of deuterium in converted to heat
energy by fusion.
Thermonuclear weapons produce energy in the same way in which the
Sun produces energy. Fast moving sub atomic particles of deuterium
(a type of hydrogen) smash into each other and bond together.
order for the particles to bond together they must be moving very
rapidly. To make the sub-atomic particles move at the required speed
they must be heated up. The temperature needed for this to occur is
not found naturally occurring on the Earth. It is around 10,000,000
deuterium atoms combine they eventually form helium. The effects of
this are to create a total mass of helium which is less than the
original mass of deuterium. This difference in mass is called the
mass defect. It is this, according to Einstein’s Law, which creates
the heat energy.
create the ignition temperature needed to start a fusion reaction,
scientists use a nuclear fission bomb within the thermonuclear
neutron bombs differs from other types of nuclear weapon in as much
as its primary lethal effects come from the radiation which it emits
after detonation. The neutron bomb is constructed in such a way that
the blast and heat effects are kept to a minimum. This weapon is
useful if enemy personnel, not structures are the intended target.
Little Boy Fission Bomb dropped on
A fission bomb uses an element such as Uranium 235. When an atom
split the amount of energy released in a very short period of time
is immense . A pound of highly enriched uranium , if used in a
nuclear bomb would create the same amount of energy as a million
gallon of petrol . When you consider a pound of uranium is about the
size of a cricket ball , and a million gallons of petrol would fill
a cube (50ft by 50ft building), you can see just how much energy is
available in a little bit of uranium.
fission bomb the fuel needs to be kept in two or more sub critical
masses. At the time of detonation these masses must be combined .
Free neutrons must be introduced to the super critical mass to start
the fission. To bring the sub critical masses together to form a
super critical mass 2 techniques are used.
These are :
Gun triggered fission bombs and
implosion triggered fission bombs.
Gun Triggered Fission
easiest way to bring 2 sub critical masses together to form a super
critical mass is to fire one into the other, A “bullet” of u-235 is
placed at one end of a tube. A sphere of sub critical mass is placed
at the other end of the tube. After the bomb is released a pressure
sensor determines the appropriate height for detonation. When the
correct altitude is reached explosives fire the bullet along the
barrel. The bullet strikes the sphere breaking a piece of foil
which, in turn allows a small pellet of polonium and beryllium to
begin emitting alpha particles . The alpha particles strike the
beryllium which frees neutrons. These neutrons then initiate
fission. This fission occurs inside a tamper, usually made from
u-238. The purpose of which is to reflect liberated neutrons back
into the fission core, increasing the efficiency of the reaction
process. Once the chain reaction is initiated providing there are
enough free neutrons to continue fission, the bomb explodes.
“Little Boy” was a gun triggered fission bomb. It was 1.5%
Although more complex to manufacture than gun triggered fission
bombs, the implosion triggered fission bomb was developed by the
Manhattan project scientists. It was found that such a device was
17% efficient, (over ten times more efficient than a gun triggered
fission bomb). Fat Man was an implosion triggered fission bomb.
Although fission bombs were devastatingly effective, scientists soon
realised that more efficient and hence, more powerful weapons, could
be designed. A number of difficulties had to be over come before a
fusion bomb could be built which actually worked. Research,
conducted largely by Edmond Teller, over came these problems. Teller
encased a fission bomb within a fusion bomb, thus creating
sufficiently high temperatures and pressures for fusion of deuterium
and tritium to occur causing vast amounts of heat and radiation to
be emitted. Fusion bombs, as well as being more efficient, could
also be made substantially smaller than fission triggered weapons.
The smaller devices could then be used in artillery shells and
smaller missiles fired from portable launchers. Thus, limited
nuclear war could be waged.
energy produced by fusion weapons is created in a similar manner to
the way which the Sun creates it’s energy. The reactions which occur
in both the Sun and fusion bombs are called Thermonuclear reactions.
neutron bomb, also known as a enhanced radiation weapon (erw), is a
small fission device. It's main purpose is to destroy living
material, whilst causing only limited damage by blast or heat.
primary effect of the weapon is emission of neutrons (hence the
name). These are lethal to living organisms within the blast area.
The design of the bomb is such, that physical structures are only
effected over a much smaller distant than conventional H-bombs.
These weapons are preferred by NATO as they limit, at least to a
small extent, the amount of collateral damage caused.