These are the easiest nuclear
weapons to design and manufacture, and the capability to do so
is a prerequisite for developing any of the other weapon
types. In addition to the five declared nuclear powers (the
U.S., the USSR/Russia, Britain, France, and China) which have
all acquired and tested these weapons, they have also been
acquired by Israel, India, South Africa, and Pakistan. India
has tested a fission bomb for sure, while Israel and South Africa are
suspected of having tested one.
Truman authorized the research and
development of a Hydrogen Bomb. Once developed, the first
Hydrogen Bomb was detonated at Eniwetok.
The Warheads themselves are only about the size
of a basketball but they pack a mighty 10 megatons worth of
This warhead is only 15 Kilotons but is still
small. Photo source:
U.S. Government /Los Alamos National Laboratory
The Mark 17 hydrogen bomb: the largest bomb ever made by the
United States. Over 24 feet long, 42,000 pounds, and with an
explosive power of 15-20 megatons (equivalent to over 1,000
Hiroshima size bombs). This one is on display at the National
Atomic Museum. CLUI photo
Neutron bombs, more formally referred to
as "enhanced radiation (ER) warheads", are small
thermonuclear weapons in which the burst of neutrons generated
by the fusion reaction is intentionally not absorbed inside
the weapon, but allowed to escape.
Neutron bombs differ from other
thermonuclear weapons in that a deuterium-tritium gas mixture
is the only fusion fuel. There are 2 reasons: the D-T
thermonuclear reaction releases 80% of its energy as neutron
kinetic energy, and it is also the easiest of all fusion
reactions to ignite. This means that only 20% of the fusion
energy is available for blast and thermal radiation
production, that the neutron flux produced consists of
extremely penetrating 14.7 Mev neutrons, and that a very small
fission explosion (250-400 tons) can be used for igniting the
reaction. The more typical lithium deuteride fuel would
produce much more blast and flash for each unit of neutron
flux, and would require a much larger fission explosion to set
it off. The disadvantage of using D-T fuel is that tritium is
very expensive, and decays at a rate of 5.5% a year. Combined
with its increased complexity this makes ER warheads more
expensive to build and maintain than other tactical nuclear
weapons. To produce a 1 Kt fusion yield 12.5 g of tritium and
5 g of deuterium are required.
The U.S. developed and produced three
neutron warheads, a fourth was cancelled prior to production.
All have been retired and dismantled.
The Soviet Union, China, and France are all
known to have developed neutron bomb designs and may have them
in service. A number of reports have claimed that Israel has
developed neutron bombs which, though they could be valuable
on an armor battleground like the Golan Heights, are difficult
to develop and require significant testing. This makes it
unlikely that Israel has in fact acquired them.