The Teller–Ulam design is the nuclear weapon design concept first developed and used by the United States and has since been used in most of the world's nuclear weapons.[1] It is colloquially referred to as "the secret of the hydrogen bomb" because it employs hydrogen fusion, though in most applications the bulk of its destructive energy comes fromuranium fission, not hydrogen fusion. Sony VAIO PCG-3B1M BatterySony VAIO PCG-3C1T Battery
It is named for its two chief contributors, Edward Teller and Stanisław Ulam, who developed it in 1951 for the United States, with certain concepts developed with the contribution of John von Neumann. It was first used in multi-megaton-range thermonuclear weapons. Sony VAIO PCG-3D1M Battery
As it is also the most efficient design concept for small nuclear weapons, today virtually all the nuclear weapons deployed by the five nuclear-weapon states under the NPT use the Teller–Ulam design.[3]
Its essential features, which officially remained secret for nearly three decades, Sony VAIO PCG-3G2M Battery
are: 1) separation of stages into a triggering "primary" explosive and a much more powerful "secondary" explosive, 2) compression of the secondary by X-rayscoming from nuclear fission in the primary, a process called the "radiation implosion" of the secondary, and 3) heating of the secondary, after cold compression, by a second fission explosion inside the secondary. Sony VAIO PCG-5R1M Battery
The radiation implosion mechanism is a heat engine exploiting the temperature difference between the secondary's hot, surrounding radiation channel and its relatively cool interior. This temperature difference is briefly maintained by a massive heat barrier called the "pusher", which also serves as an implosion tamper, increasing and prolonging the compression of the secondary. Sony VAIO PCG-7141M Battery
If made of uranium—and it usually is—it can capture neutrons produced by the fusion reaction and undergo fission itself, increasing the overall explosive yield. In many Teller–Ulam weapons, fission of the pusher dominates the explosion and produces radioactive fission product fallout. Sony VAIO PCG-7143M Battery
The first test of this principle was the "Ivy Mike" nuclear test in 1952, conducted by the United States. In the Soviet Union, the design was known as Andrei Sakharov's "Third Idea", first tested in 1955. Similar devices were developed by the United Kingdom, China, and France, though no specific code names are known for their designs. Sony VAIO PCG-7151M Battery
Detailed knowledge of fission and fusion weapons is classified to some degree in virtually every industrialized nation. In the United States, such "knowledge" can by default be classified as Restricted Data, even if it is created by persons who are not government employees or associated with weapons programs, Sony VAIO PCG-7154M Battery
in a legal doctrine known as "born secret" (though the constitutional standing of the doctrine has been at times called into question, see United States v. The Progressive). Born secret is rarely invoked for cases of private speculation. The official policy of the United States Department of Energy has been not to acknowledge the leaking of design information, Sony VAIO PCG-7162M Battery
as such acknowledgment would potentially validate the information as accurate. In a small number of prior cases, the U.S. government has attempted to censor weapons information in the public press, with limited success.
Though large quantities of vague data have been officially released, Sony VAIO PCG-7181M Battery
and larger quantities of vague data have been unofficially leaked by former bomb designers, most public descriptions of nuclear weapon design details rely to some degree on speculation,reverse engineering from known information, or comparison with similar fields of physics (inertial confinement fusion is the primary example). Sony VAIO PCG-41112M Battery
Such processes have resulted in a body of unclassified knowledge about nuclear bombs which is generally consistent with official unclassified information releases, related physics, and is thought to be internally consistent, though there are some points of interpretation which are still considered open. Sony VAIO PCG-7153M Battery
The state of public knowledge about the Teller–Ulam design has been mostly shaped from a few specific incidents outlined in a section below.
The basic principle of the Teller–Ulam configuration is the idea that different parts of a thermonuclear weapon can be chained together in "stages", Sony VAIO PCG-71312M Battery
with the detonation of each stage providing the energy to ignite the next stage. At a bare minimum, this implies a primary section which consists of a fission bomb (a "trigger"), and a secondary section which consists of fusion fuel. The energy released by the primary compresses the secondary through a process called "radiation implosion", Sony VAIO PCG-7144M Battery
at which point it is heated and undergoes nuclear fusion. Because of the staged design, it is thought that a tertiary section, again of fusion fuel, could be added as well, based on the same principle as the secondary; the AN602 "Tsar Bomba" is thought to have been a three-stage device. Sony VAIO PCG-7191L Battery
Surrounding the other components is a hohlraum or radiation case, a container which traps the first stage or primary's energy inside temporarily. The outside of this radiation case, which is also normally the outside casing of the bomb, is the only direct visual evidence publicly available of any thermonuclear bomb component's configuration. Sony VAIO PCG-3C1M Battery
Numerous photographs of various thermonuclear bomb exteriors have been declassified.[4]
The primary is thought to be a standard implosion method fission bomb, though likely with a core boosted by small amounts of fusion fuel (usually 50/50% deuterium/tritium gas) for extra efficiency; Sony VAIO PCG-3F1M Battery
the fusion fuel releases excess neutrons when heated and compressed, inducing additional fission. Generally, a research program with the capacity to create a thermonuclear bomb has already mastered the ability to engineer boosted fission. When fired, Sony VAIO PCG-3H1M Battery
the plutonium-239 (Pu-239) and/or uranium-235 (U-235) core would be compressed to a smaller sphere by special layers of conventional high explosives arranged around it in anexplosive lens pattern, initiating the nuclear chain reaction that powers the conventional "atomic bomb".Sony VAIO PCG-3J1M Battery
The secondary is usually shown as a column of fusion fuel and other components wrapped in many layers. Around the column is first a "pusher-tamper", a heavy layer of uranium-238 (U-238) or lead which serves to help compress the fusion fuel (and, in the case of uranium, may eventually undergo fission itself). Sony VAIO PCG-8141M Battery
Inside this is the fusion fuel itself, usually a form of lithium deuteride, which is used because it is easier to weaponize than liquified tritium/deuterium gas (compare the success of the cryogenic deuterium-based Ivy Mike experiment to the (over)success of the lithium deuteride-based Castle Bravo experiment). Sony VAIO PCG-8161M Battery
This dry fuel, when bombarded by neutrons, produces tritium, a heavy isotope of hydrogen which can undergo nuclear fusion, along with the deuterium present in the mixture. (See the article on nuclear fusion for a more detailed technical discussion of fusion reactions.) Sony VAIO PCG-3C2M Battery
Inside the layer of fuel is the "spark plug", a hollow column of fissile material (plutonium-239 or uranium-235) which, when compressed, can itself undergo nuclear fission (because of the shape, it is not acritical mass without compression). The tertiary, if one is present, would be set below the secondary and probably be made up of the same materials. Sony VAIO PCG-5N2M Battery
Separating the secondary from the primary is the interstage. The fissioning primary produces four types of energy: 1) expanding hot gases from high explosive charges which implode the primary; 2) superheated plasma that was originally the bomb's fissile material and its tamper; 3) Sony VAIO PCG-5P1M Battery
the electromagnetic radiation; and 4) the neutrons from the primary's nuclear detonation. The interstage is responsible for accurately modulating the transfer of energy from the primary to the secondary. It must direct the hot gases, plasma, electromagnetic radiation and neutrons toward the right place at the right time. Sony VAIO PCG-5S1M Battery
Less than optimal interstage designs have resulted in the secondary failing to work entirely on multiple shots, known as a "fissile fizzle". The Koon shot of Operation Castle is a good example; a small flaw allowed the neutron flux from the primary to prematurely begin heating the secondary, weakening the compression enough to prevent any fusion. Sony VAIO PCG-9Z1M Battery
There is very little detailed information in the open literature about the mechanism of the interstage. One of the best sources is a simplified diagram of a British thermonuclear weapon similar to the American W76 warhead. It was released by Greenpeace in a report titled "Dual Use Nuclear Technology".[7] Sony VAIO PCG-7171M Battery
The major components and their arrangement are in the diagram, though details are almost absent; what scattered details it does include likely have intentional omissions and/or inaccuracies. They are labeled "End-cap and Neutron Focus Lens" and "Reflector Wrap"; the former channels neutrons to the U-235/Pu-239 Spark Plug while the latter refers to an X-ray reflector; Sony VAIO PCG-7186M Battery
typically a cylinder made out of an X-ray opaque material such as uranium with the primary and secondary at either end. It does not reflect like a mirror; instead, it gets heated to a high temperature by the X-ray flux from the primary, then it emits more evenly spread X-rays which travel to the secondary, causing what is known as radiation implosion. Sony VAIO PCG-81112M Battery
In Ivy Mike, gold was used as a coating over the uranium to enhance the blackbody effect. [8]Next comes the "Reflector/Neutron Gun Carriage". The reflector seals the gap between the Neutron Focus Lens (in the center) and the outer casing near the primary. Sony VAIO PCG-31311M Battery
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