What is an atomic bomb?
There are two basic types of nuclear weapons: those that get
most of their energy from nuclear fission
reactions alone, and those that use fission reactions to begin
nuclear fusion reactions that produce a huge
The fission type bombs are called atomic bombs or atom bombs
(abbreviated as A-bombs).
In fission weapons, a mass enriched uranium or plutonium is brought
to a supercritical mass (the
amount of material needed to start a nuclear chain reaction) either
by shooting one piece
of sub-critical material into another (the "gun" method) or by
squeezing together sub-critical spheres
by using chemical explosives (the "implosion" method).
The fission way can be only be used if the fissile material is
A major challenge in all nuclear weapon designs is to make sure
that a very large fraction of the fuel is consumed before the
weapon destroys itself.
The amount of energy released by fission bombs can range from the
equivalent of just under
a ton of TNT, to upwards of 500,000 tons (500 kilotons) of
All fission reactions produce radioactive remains. Many fission
products are either highly radioactive (but short-lived) or
moderately radioactive (but long-lived). That makes them a form of
radioactive contamination if not fully contained.
Fission products are the principal radioactive component of nuclear
The most commonly used fissile materials for nuclear weapons have
been uranium-235 and plutonium-239. Less commonly used has been
uranium-233. Neptunium-237 and some isotopes of americium may be
An atomic bomb is any bomb which obtains its destructive energy
from the excess binding energy of atomic nuclei. The term is
most commonly applied to bombs that release the excess binding
energy of heavy atoms by fissioning them to form lighter atoms, but
can equally correctly be applied to bombs that release the excess
binding energy of light atoms by fusing them to form heavier atoms
(however such bombs are most commonly called hydrogen bombs).
The fine details of this are somewhat blurred as most modern
nuclear weapons use some combination of both fission and fusion,
regardless of what they are called (e.g. dial-a-yield tritium gas
fusion boosted atomic bombs, conventionally built hydrogen fusion
bombs usually get more than 90% of their yield from fast fission of
their depleted uranium tamper) to optimize their