Variable yield, or dial-a-yield, is an option available on most modern
nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear exp ...
s. It allows the operator to specify a weapon's
yield, or explosive power, allowing a single design to be used in different situations. For example, the
Mod-10 B61 bomb had selectable explosive yields of 0.3, 5, 10 or 80 kilotons, depending on how the ground crew set a dial inside the casing when it was loaded onto an aircraft.
Technology
Variable yield technology has existed since at least the late 1950s. Examples of variable yield weapons include the
B61 nuclear bomb
The B61 nuclear bomb is the primary thermonuclear weapon, thermonuclear gravity bomb in the United States Enduring Stockpile following the end of the Cold War. It is a low-to-intermediate yield strategic nuclear weapon, strategic and tactical nuc ...
family,
B83,
B43,
W80,
W85, and
WE177A warheads.
Most modern nuclear weapons are
Teller–Ulam design
A thermonuclear weapon, fusion weapon or hydrogen bomb (H-bomb) is a second-generation nuclear weapon design. Its greater sophistication affords it vastly greater destructive power than first-generation nuclear bombs, a more compact size, a lowe ...
type
thermonuclear weapon
A thermonuclear weapon, fusion weapon or hydrogen bomb (H-bomb) is a second-generation nuclear weapon design. Its greater sophistication affords it vastly greater destructive power than first-generation nuclear bombs, a more compact size, a lowe ...
s, with a
fission ''primary'' stage and a
fusion ''secondary stage'' that is collapsed by the energy from the primary. These offer at least three methods to vary yield:
* Varying primary yield by
boosting with
fusion, using small amounts of
deuterium
Deuterium (hydrogen-2, symbol H or D, also known as heavy hydrogen) is one of two stable isotopes of hydrogen; the other is protium, or hydrogen-1, H. The deuterium nucleus (deuteron) contains one proton and one neutron, whereas the far more c ...
/
tritium
Tritium () or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with a half-life of ~12.33 years. The tritium nucleus (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus of the ...
(DT) gas inside the primary fission bomb to increase its yield by supplying additional neutrons from DT fusion at the beginning of the fission process. Typically, the gas is injected a few seconds before detonation and the amount used can be preset{{snde.g., zero, 25%, 50%, or all of the gas.
* Changing the primary yield by varying the timing or use of
external neutron initiator
Neutron generators are neutron source devices which contain compact linear particle accelerators and that produce neutrons by fusing isotopes of hydrogen together. The fusion reactions take place in these devices by accelerating either deuter ...
s (ENIs).
[4.1.8.2 External Neutron Initiators (ENIs)](_blank)
Nuclear Weapons FAQ, accessed 2009-06-17 These are small particle accelerators that cause a brief fusion reaction by accelerating deuterium into a tritium target (or potentially vice versa), producing a short pulse of energetic neutrons. Precise timing of the ENI pulse as the nuclear primary's pit is collapsing can significantly affect yield, and the rate of neutron injection can also be controlled.
* Shutting down the thermonuclear secondary, either by firing the primary at low enough yield that it does not compress the secondary sufficiently to ignite, or by blocking energy transport inside the warhead briefly as the primary is firing using shutters or a similar mechanism. If the primary's energy starts to disperse through the radiation case before being focused on the secondary then the secondary will likely never detonate.
All current
British nuclear warheads incorporate variable yield technology as standard.
Summary of UK Arsenal report
/ref>
See also
*Nuclear weapon design
Nuclear weapons design are physical, chemical, and engineering arrangements that cause the physics package of a nuclear weapon to detonate. There are three existing basic design types:
# Pure fission weapons are the simplest, least technically de ...
References
External links
nuclear weapons archive
Nuclear weapons