Pit (nuclear weapon) - AbsoluteAstronomy.com

The pit is the core of an implosion weapon – the fissile material and any neutron reflector

Neutron reflector

A neutron reflector is any material that reflects neutrons. This refers to elastic scattering rather than to a specular reflection. The material may be graphite, beryllium, steel, and tungsten carbide, or other materials...

or tamper bonded to it. Some weapons tested during the 1950s used pits made with U-235

Uranium-235

- References :* .* DOE Fundamentals handbook: Nuclear Physics and Reactor theory , .* A piece of U-235 the size of a grain of rice can produce energy equal to that contained in three tons of coal or fourteen barrels of oil. -External links:* * * one of the earliest articles on U-235 for the...

alone, or in composite

Composite material

Composite materials, often shortened to composites or called composition materials, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or...

with plutonium

Plutonium

Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...

, but all-plutonium pits are the smallest in diameter and have been the standard since the early 1960s.

Pit designs

The pits of the first nuclear weapons were solid, with an urchin

Urchin (detonator)

A modulated neutron initiator is a neutron source capable of producing a burst of neutrons on activation. It is a crucial part of some nuclear weapons, as its role is to "kick-start" the chain reaction at the optimal moment when the configuration is prompt critical. It is also known as an internal...

neutron initiator in their center. The gadget and Fat Man

Fat Man

"Fat Man" is the codename for the atomic bomb that was detonated over Nagasaki, Japan, by the United States on August 9, 1945. It was the second of the only two nuclear weapons to be used in warfare to date , and its detonation caused the third man-made nuclear explosion. The name also refers more...

used pits made of solid hot pressed

Hot pressing

Hot pressing is a high-pressure, low-strain-rate powder metallurgy process for forming of a powder or powder compact at a temperature high enough to induce sintering and creep processes. This is achieved by the simultaneous application of heat and pressure....

material (at 400°C and 200 MPa in steel dies) half-spheres of 9.2 cm diameter, with a 2.5 cm internal cavity for the initiator. The gadget's pit was electroplated

Electroplating

Electroplating is a plating process in which metal ions in a solution are moved by an electric field to coat an electrode. The process uses electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material, such as a metal...

with 0.13 mm of silver; the layer, however, developed blistering and the blisters had to be ground and plated with gold leaf before the test. The Fat Man pit, and those of subsequent models, were all plated with nickel. A hollow pit was considered but ultimately rejected due to higher requirements for implosion accuracy.

Later designs used TOM initiators of similar design but with diameters of only about 1 cm. The internal neutron initiators were later phased out and replaced with pulsed neutron source

Neutron source

A Neutron source is a device that emits neutrons. There is a wide variety of different sources, ranging from hand-held radioactive sources to neutron research facilities operating research reactors and spallation sources...

s, and with boosted fission weapons.

Efficiency of the implosion can be increased by leaving an empty space between the tamper and the pit, causing a rapid acceleration of the shock wave before it impacts the pit. This method is known as levitated-pit implosion. Levitated pits were tested in 1948 with Fat Man style bombs, and became obsolete with the advent of hollow pits.

The early weapons with a levitated pit had a removable pit, called an open pit. It was stored separately, in a special capsule called a birdcage.

During implosion of a hollow pit, the plutonium layer accelerates inwards, colliding in the middle and forming a supercritical highly dense sphere. Due to the added momentum, the plutonium itself plays part of the role of the tamper, requiring a smaller amount of uranium in the tamper layer, reducing the warhead weight and size.

The efficiency of the hollow pits can be further increased by injecting a 50%/50% mixture of deuterium

Deuterium

Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

and tritium

Tritium

Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...

into the cavity immediately before the implosion, so called "boosting"

Boosted fission weapon

A boosted fission weapon usually refers to a type of nuclear bomb that uses a small amount of fusion fuel to increase the rate, and thus yield, of a fission reaction. The neutrons released by the fusion reactions add to the neutrons released in the fission, as well as inducing the fission reactions...

; this also lowers the minimum amount of plutonium for achieving a successful explosion. The higher degree of control of the initiation, both by the amount of deuterium-tritium mixture injection and by timing and intensity of the neutron pulse from the external generator, facilitated the design of variable yield

Variable yield

Variable yield — or dial-a-yield — is an option available on most modern nuclear weapons. It allows the operator to specify a weapon's yield, or explosive power, allowing a single design to be used in different situations...

weapons.

The yield of a weapon can also be controlled by selecting among a choice of pits. For example, the Mark 4 nuclear bomb

Mark 4 nuclear bomb

The Mark 4 nuclear bomb was an American nuclear bomb design produced starting in 1949 and in use until 1953.The Mark 4 was based on the earlier Mark 3 Fat Man design, used in the Trinity test and the bombing of Nagasaki...

can be equipped with three different pits: 49-LTC-C (levitated uranium-235), 49-LCC-C (levitated composite uranium-plutonium), and 50-LCC-C (levitated composite). This approach is not suitable for field selectability of the yield of the more modern weapons with nonremovable pits, but allows production of multiple weapon subtypes with different yields for different tactical uses.

The early US designs were based on standardized Type C and Type D pit assemblies. The Mark 4

Mark 4 nuclear bomb

bomb used the Type C and Type D pits, which were insertable manually in flight. The Mark 5

Mark 5 nuclear bomb

The Mark 5 nuclear bomb and W5 nuclear warhead were a common core nuclear weapon design, designed in the early 1950s and which saw service from 1952 to 1963....

bomb used Type D pits, with automated in-flight insertion; the W-5 warhead used the same. Its successor, the Mark 6

Mark 6 nuclear bomb

The Mark 6 nuclear bomb was an American nuclear bomb based on the earlier Mark 4 nuclear bomb and its predecessor, the Mark 3 Fat Man nuclear bomb design.The Mark 6 was produced from 1951-1955 and saw service until 1962...

bomb, presumably used the same or similar pits.

The pit can be composed of plutonium-239, plutonium-239/uranium-235 composite, or uranium-235 only. Plutonium is the most common choice, but e.g. the Violet Club

Violet Club

Violet Club was a nuclear weapon deployed by the United Kingdom during the cold war. It was Britain's first operational "high yield" weapon, and was intended to provide an emergency capability until a thermonuclear weapon could be developed from the 1956-1958 Operation Grapple thermonuclear tests...

bomb and Orange Herald

Orange Herald

- Technical :Orange Herald was a fusion boosted British fission nuclear weapon, comprising a U-235 primary surrounded by lithium deuteride. 'Herald' was suitable for mounting on a missile, utilizing 117 kg of U-235...

warhead used massive hollow pits, consisting of 87 and 117 kg (98 and 125 kg according to other sources) of highly enriched uranium. The Green Grass fission core consisted of a sphere of highly enriched uranium, with inner diameter of 560 mm, wall thickness of 3.6 mm and mass of 70–86 kg; the pit was completely supported by the surrounding natural uranium tamper. Such massive pits, consisting of more than one critical mass of fissile material, present a significant safety risk, as even an asymmetrical detonation of the implosion shell may cause a kiloton-range explosion. The largest-yield pure-fission weapon, the 500-kiloton Mark 18 nuclear bomb

Mark 18 nuclear bomb

The Mark 18 nuclear bomb, also known as the SOB or Super Oralloy Bomb, was an American nuclear bomb design which was the highest yield fission bomb produced by the US. The Mark 18 had a design yield of 500 kilotons...

, used a hollow pit composed of more than 60 kg of highly enriched uranium, about four critical masses; the safing was done with an aluminium

Aluminium

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

–boron

Boron

Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...

chain inserted in the pit.

A sealed pit means that a solid metal barrier is formed around the pit inside a nuclear weapon, with no openings. This protects the nuclear materials from environmental degradation and helps reduce the chances of their release in case of an accidental fire or minor explosion. The first US weapon employing a sealed pit was the W25 warhead. The metal is often stainless steel

Stainless steel

In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....

, but beryllium

Beryllium

Beryllium is the chemical element with the symbol Be and atomic number 4. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl and chrysoberyl...

, aluminium

Aluminium

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

, and possibly vanadium

Vanadium

Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery gray, ductile and malleable transition metal. The formation of an oxide layer stabilizes the metal against oxidation. The element is found only in chemically combined form in nature...

are also used. Beryllium is brittle, toxic and expensive, but is an attractive choice due to its role as a neutron reflector

Neutron reflector

, lowering the needed critical mass of the pit. There is probably a layer of interface metal between plutonium and beryllium, capturing the alpha particles from decay of plutonium (and americium and other contaminants) which would otherwise react with the beryllium and produce neutrons. Beryllium tampers/reflectors came into use in the mid-1950s; the parts were machined from pressed powder beryllium blanks in the Rocky Flats Plant

Rocky Flats Plant

The Rocky Flats Plant was a United States nuclear weapons production facility near Denver, Colorado that operated from 1952 to 1992. It was under the control of the United States Atomic Energy Commission until 1977, when it was replaced by the Department of Energy .-1950s:Following World War II,...

.

More modern plutonium pits are hollow. An often-cited specification applicable to some modern pits describes a hollow sphere of a suitable structural metal, of the approximate size and weight of a bowling ball

Bowling ball

A bowling ball is a spherical ball made from plastic, reactive resin, urethane or a combination of these materials which is used in the sport of bowling. Ten-pin bowling balls generally have a set of three holes drilled in them, one each for the ring and middle finger, and one for the thumb;...

, with a channel for injection of tritium

Tritium

Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...

(in the case of boosted fission weapon

Boosted fission weapon

s), with the internal surface lined with plutonium. The size, usually between a bowling ball and a tennis ball

Tennis ball

A tennis ball is a ball designed for the sport of tennis,approximately 6.7 cm in diameter. Tennis balls are generally bright green, but in recreational play can be virtually any color. Tennis balls are covered in a fibrous fluffy felt which modifies their aerodynamic properties...

, accuracy of sphericity, and weight and isotopic composition of the fissile material, the principal factors influencing the weapon properties, are often classified. The hollow pits can be made of half shells with three joint weld

Weld

Weld most commonly refers to a joint formed by welding.Weld may also refer to:-People:* Weld family, an extended family of New England** Theodore Dwight Weld** Tuesday Weld* Weld-Blundell family* Cecil Weld-Forester, 1st Baron Forester...

s around the equator, and a tube brazed

Brazing

Brazing is a metal-joining process whereby a filler metal is heated above and distributed between two or more close-fitting parts by capillary action. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere, usually a flux...

(to beryllium or aluminium shell) or electron beam

Electron beam welding

Electron beam welding is a fusion welding process in which a beam of high-velocity electrons is applied to the materials being joined. The workpieces melt as the kinetic energy of the electrons is transformed into heat upon impact, and the filler metal, if used, also melts to form part of the weld...

or TIG-welded (to stainless steel shell) for injection of the boost gas. Beryllium-clad pits are more vulnerable to fracture, more sensitive to temperature fluctuations, more likely to require cleaning, susceptible to corrosion

Corrosion

Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...

with chlorides and moisture, and can expose workers to toxic beryllium.

Newer pits contain about 3 kilograms of plutonium. Older pits used about 4-5 kilograms.

Further miniaturization was achieved by linear implosion. An elongated subcritical solid pit, reshaped into a supercritical spherical shape by two opposite shock waves, and later a hollow pit with more precisely shaped shock waves, allowed construction of relatively very small nuclear warheads. The configuration was, however, considered prone to accidental high-yield detonation when the explosive gets accidentally initiated, unlike a spherical implosion assembly where asymmetric implosion just scatters the pit around. This necessitated special design precautions, and a series of safety tests, including one-point safety. Non-spherical pits are a significant technological advancement, making it possible to design smaller, lighter nuclear devices, suitable for e.g. multiple independently targetable reentry vehicle

Multiple independently targetable reentry vehicle

A multiple independently targetable reentry vehicle warhead is a collection of nuclear weapons carried on a single intercontinental ballistic missile or a submarine-launched ballistic missile . Using a MIRV warhead, a single launched missile can strike several targets, or fewer targets redundantly...

s. Miniaturized warheads that employ linear implosion design, e.g. the W88

W88

The W88 is a United States thermonuclear warhead, with an estimated yield of 475 kiloton , and is small enough to fit on MIRVed missiles. The W88 was designed at the Los Alamos National Laboratory in the 1970s. In 1999 the director of Los Alamos who had presided over its design described it as...

, frequently use non-spherical, oblate spheroid pits. This configuration was first used in W47

W47

The W47 was an American thermonuclear warhead used on the Polaris A-1 sub-launched ballistic missile system. Various models were in service from 1960 through the end of 1974...

.

In September 1992, China allegedly performed a successful nuclear test of a non-spherical pit, a crucial technological advancement.

Pits can be shared between weapon designs. For example, the W89

W89

The W89 was an American thermonuclear warhead design intended for use on the AGM-131 SRAM II air to ground nuclear missile.What was to become the W89 design was awarded to the Lawrence Livermore National Laboratory in the mid-1980s. It entered Phase 2A technical definition and cost study in...

warhead is said to reuse pits from the W68

W68

The W68 warhead was the warhead used on the UGM-73 Poseidon SLBM missile. It was developed in the late 1960s at Lawrence Livermore National Laboratory.-Specifications:The W68 weighs...

s. Many pit designs are standardized and shared between different physics packages; the same physics packages are often used in different warheads. Pits can be also reused; the sealed pits extracted from disassembled weapons are commonly stockpiled for direct reuse. Due to low aging rates of the plutonium-gallium alloy, the shelf life of pits is estimated to be a century or more. The oldest pits in the US arsenal are still less than 50 years old.

The sealed pits can be classified as bonded or non-bonded. Non-bonded pits can be disassembled mechanically; a lathe

Lathe

A lathe is a machine tool which rotates the workpiece on its axis to perform various operations such as cutting, sanding, knurling, drilling, or deformation with tools that are applied to the workpiece to create an object which has symmetry about an axis of rotation.Lathes are used in woodturning,...

is sufficient for separating the plutonium. Recycling of bonded pits requires chemical processing.

Pits of modern weapons are said to have radii of about 5 cm.

Weapons and pit types

Weapons and pit types
Design lab	Weapon	Pit type	Status	Used in	Comment
LANL	B61 B61 nuclear bomb The B61 nuclear bomb is the primary thermonuclear weapon in the U.S. Enduring Stockpile following the end of the Cold War. It is an intermediate yield strategic and tactical nuclear weapon featuring a two-stage radiation implosion design.... -3,4,10	123	Enduring Stockpile Enduring Stockpile The "Enduring Stockpile" is the United States's arsenal of nuclear weapons following the end of the Cold War.During the Cold War the United States produced over 70,000 nuclear weapons. By its end the U.S. stockpile was about 23,000 weapons of 26 different types...	bomb
LANL	B61 B61 nuclear bomb The B61 nuclear bomb is the primary thermonuclear weapon in the U.S. Enduring Stockpile following the end of the Cold War. It is an intermediate yield strategic and tactical nuclear weapon featuring a two-stage radiation implosion design.... -7,11	125	Enduring Stockpile	bomb
LANL	B61 B61 nuclear bomb The B61 nuclear bomb is the primary thermonuclear weapon in the U.S. Enduring Stockpile following the end of the Cold War. It is an intermediate yield strategic and tactical nuclear weapon featuring a two-stage radiation implosion design.... -4	118	Enduring Stockpile	bomb
LANL	W76 W76 The W76 is a United States thermonuclear warhead. It was manufactured from 1978-1987, and is still in service .The W-76 is carried inside a Mk-4 re-entry vehicle. U.S...	116	Enduring Stockpile	Trident I and Trident II SLBM	most heat-sensitive LANL design
LANL	W78 W78 The W78 thermonuclear warhead is the warhead used on most of the United States LGM-30G Minuteman III intercontinental ballistic missiles , along with the MK-12A reentry vehicle which carried the warhead. Minuteman III's initially deployed with the older W62 warhead; the W78 was deployed starting...	117	Enduring Stockpile	LGM-30 Minuteman LGM-30 Minuteman The LGM-30 Minuteman is a U.S. nuclear missile, a land-based intercontinental ballistic missile . As of 2010, the version LGM-30G Minuteman-III is the only land-based ICBM in service in the United States... ICBM
LANL	W80	124	Enduring Stockpile	very similar to W84, modification of B61; AGM-86, AGM-129, BGM-109 Tomahawk BGM-109 Tomahawk The Tomahawk is a long-range, all-weather, subsonic cruise missile. Introduced by General Dynamics in the 1970s, it was designed as a medium- to long-range, low-altitude missile that could be launched from a surface platform. It has been improved several times and, by way of corporate divestitures...	responsibility being transferred to LLNL
LANL	W80	119	Enduring Stockpile	very similar to W84, modification of B61; AGM-86, AGM-129, BGM-109 Tomahawk BGM-109 Tomahawk The Tomahawk is a long-range, all-weather, subsonic cruise missile. Introduced by General Dynamics in the 1970s, it was designed as a medium- to long-range, low-altitude missile that could be launched from a surface platform. It has been improved several times and, by way of corporate divestitures...
LANL	W80-0		Enduring Stockpile	BGM-109 Tomahawk BGM-109 Tomahawk The Tomahawk is a long-range, all-weather, subsonic cruise missile. Introduced by General Dynamics in the 1970s, it was designed as a medium- to long-range, low-altitude missile that could be launched from a surface platform. It has been improved several times and, by way of corporate divestitures...	supergrade plutonium, low radiation, for submarines
LANL	W88 W88 The W88 is a United States thermonuclear warhead, with an estimated yield of 475 kiloton , and is small enough to fit on MIRVed missiles. The W88 was designed at the Los Alamos National Laboratory in the 1970s. In 1999 the director of Los Alamos who had presided over its design described it as...	126	Enduring Stockpile	Trident II SLBM	linear implosion, non-spherical pit
LLNL	B83 B83 nuclear bomb The B83 nuclear weapon is a variable yield gravity bomb developed by the United States in the late 1970s, entering service in 1983. With a maximum yield of 1.2 megatons, it is currently the most powerful atomic weapon in the US arsenal...	MC3350	Enduring Stockpile	gravity bomb	heaviest pit, fire-resistant pit
LLNL	W62 W62 The W62 is an American thermonuclear warhead designed in the late 1960s and manufactured from 1970 to 1976, used on some Minuteman III ICBMs and retired in 2010....	MC2406	Enduring Stockpile	LGM-30 Minuteman LGM-30 Minuteman The LGM-30 Minuteman is a U.S. nuclear missile, a land-based intercontinental ballistic missile . As of 2010, the version LGM-30G Minuteman-III is the only land-based ICBM in service in the United States... ICBM
LLNL	W84 W84 The W84 is an American thermonuclear warhead designed for use on the BGM-109G Gryphon Ground Launched Cruise Missile . It is a derivative of the B61 nuclear bomb design and a close relative of the W80 warhead used on the AGM-86 ALCM, AGM-129 ACM, and BGM-109 Tomahawk SLCM cruise missiles.The W84...	?	Enduring Stockpile	very similar to W80; BGM-109G GLCM	fire-resistant pit
LLNL	W87 W87 The W87 is an American thermonuclear missile warhead. It was created for use on the MX or Peacekeeper ICBM, 50 of which, with up to 12 warheads per missile, were deployed during the 1986-2005 period...	MC3737	Enduring Stockpile	LGM-118A Peacekeeper LGM-118A Peacekeeper The LGM-118A Peacekeeper, also known as the MX missile , was a land-based ICBM deployed by the United States starting in 1986. A total of 50 missiles were deployed. They have since been deactivated....	fire-resistant pit
LANL	B28 B28 nuclear bomb The B28, originally Mark 28, was a thermonuclear bomb carried by U.S. tactical fighter bombers and bomber aircraft. From 1962 to 1972 under the NATO nuclear weapons sharing program, American B28s also equipped six Europe-based Canadian CF-104 squadrons known as the RCAF Nuclear Strike Force...	83	retired	bomb
LANL	B28-0 B28 nuclear bomb The B28, originally Mark 28, was a thermonuclear bomb carried by U.S. tactical fighter bombers and bomber aircraft. From 1962 to 1972 under the NATO nuclear weapons sharing program, American B28s also equipped six Europe-based Canadian CF-104 squadrons known as the RCAF Nuclear Strike Force...	93	retired	bomb	minimum decay heat Decay heat Decay heat is the heat released as a result of radioactive decay. This is when the radiation interacts with materials: the energy of the alpha, beta or gamma radiation is converted into the thermal movement of atoms.-Natural occurrence:...
LANL	B43 B43 nuclear bomb The B43 was a United States air-dropped variable yield nuclear weapon used by a wide variety of fighter bomber and bomber aircraft.The B43 was developed from 1956 by Los Alamos National Laboratory, entering production in 1959. It entered service in April 1961. Total production was 2,000 weapons,...	79	retired	bomb	beryllium-clad
LANL	B43-1 B43 nuclear bomb The B43 was a United States air-dropped variable yield nuclear weapon used by a wide variety of fighter bomber and bomber aircraft.The B43 was developed from 1956 by Los Alamos National Laboratory, entering production in 1959. It entered service in April 1961. Total production was 2,000 weapons,...	101	retired	Tsetse primary Tsetse primary The Tsetse was the common design nuclear fission bomb core for several Cold War designs for American nuclear and thermonuclear weapons, according to researcher Chuck Hansen.... ; bomb	beryllium-clad
LANL	W33	?	retired	8" nuclear artillery Nuclear artillery Nuclear artillery is a subset of limited-yield tactical nuclear weapons, in particular those weapons that are launched from the ground at battlefield targets... shell
LANL	W44 W44 The W44 was an American nuclear warhead used on the ASROC tactical anti-submarine missile system.The W44 had basic dimensions of 13.75 inches diameter and 25.3 inches length, a weight of 170 pounds, and a yield of 10 kilotons....	74	retired	Tsetse primary Tsetse primary The Tsetse was the common design nuclear fission bomb core for several Cold War designs for American nuclear and thermonuclear weapons, according to researcher Chuck Hansen.... ; RUR-5 ASROC antisubmarine	beryllium-clad
LANL	W44 W44 The W44 was an American nuclear warhead used on the ASROC tactical anti-submarine missile system.The W44 had basic dimensions of 13.75 inches diameter and 25.3 inches length, a weight of 170 pounds, and a yield of 10 kilotons.... -1	100	retired	Tsetse primary Tsetse primary The Tsetse was the common design nuclear fission bomb core for several Cold War designs for American nuclear and thermonuclear weapons, according to researcher Chuck Hansen....	beryllium-clad
LANL	W50-1 W50 (atomic weapon) The W-50 or W50 thermonuclear warhead was a nuclear bomb used on the MGM-31 Pershing intermediate range nuclear missile.There were two major variants produced , in three yield options .All variants were in diameter and long, weighing .The W50 used the Tsetse primary design...	103	retired	Tsetse primary Tsetse primary The Tsetse was the common design nuclear fission bomb core for several Cold War designs for American nuclear and thermonuclear weapons, according to researcher Chuck Hansen.... ; MGM-31 Pershing IRBM
LANL	B54	81	retired	bomb	require cleaning before long-term storage
LANL	B54-1	96	retired	bomb	require cleaning before long-term storage
LANL	B57 B57 nuclear bomb The B57 nuclear bomb was a tactical nuclear weapon developed by the United States during the Cold War.Entering production in 1963 as the Mk 57, the bomb was designed to be dropped from high-speed tactical aircraft. It had a streamlined casing to withstand supersonic flight. It was 3 m long, with a...	104	retired	Tsetse primary Tsetse primary The Tsetse was the common design nuclear fission bomb core for several Cold War designs for American nuclear and thermonuclear weapons, according to researcher Chuck Hansen.... ; bomb
LANL	W59 W59 The W59 was an American thermonuclear warhead used on some Minuteman I ICBM missiles from 1962-1969.The W59 was 16.3 inches in diameter and 47.8 inches long, and it weighed 550 pounds...	90	retired	Tsetse primary Tsetse primary The Tsetse was the common design nuclear fission bomb core for several Cold War designs for American nuclear and thermonuclear weapons, according to researcher Chuck Hansen.... ; Minuteman I ICBM
LANL	B61-0 B61 nuclear bomb The B61 nuclear bomb is the primary thermonuclear weapon in the U.S. Enduring Stockpile following the end of the Cold War. It is an intermediate yield strategic and tactical nuclear weapon featuring a two-stage radiation implosion design....	110	retired	bomb
LANL	B61 B61 nuclear bomb The B61 nuclear bomb is the primary thermonuclear weapon in the U.S. Enduring Stockpile following the end of the Cold War. It is an intermediate yield strategic and tactical nuclear weapon featuring a two-stage radiation implosion design.... -2,5	114	retired	bomb
LANL	W66 W66 The W66 thermonuclear warhead was used on the Sprint anti-ballistic missile system, designed to be a short range interceptor to shoot down incoming ICBM warheads....	112	retired	Sprint Sprint (missile) The Sprint was a two-stage, solid-fuel anti-ballistic missile, armed with a W66 enhanced radiation thermonuclear warhead. It was designed as the short-range high-speed counterpart to the longer-range LIM-49 Spartan as part of the Sentinel program. Sentinel never became operational, but the... antiballistic missile
LANL	W69 W69 W69 is a United States nuclear warhead used in AGM-69 SRAM Short-Range Attack Missiles.It was designed in the early 1970s and produced from 1974 to 1976. It remained in service until 1991, with the last units being retired in 1996...	111	retired	AGM-69 SRAM AGM-69 SRAM The Boeing AGM-69 SRAM was a nuclear air-to-surface missile designed to replace the older AGM-28 Hound Dog stand-off missile....
LANL	W85 W85 The W85 was a thermonuclear warhead developed by the United States of America to arm the Pershing II missile. It had a variable yield— often referred to as "dial-a-yield" — which could be set between 5 and 80 kilotons.-Overview:...	128	retired	Pershing II
LLNL	W48 W48 The W48 was an American nuclear artillery shell, fired from a standard 155 mm howitzer e.g. the M114 or M198. It was manufactured starting in 1963, and all units were retired in 1992....	MC1397	retired	6.1" nuclear artillery Nuclear artillery Nuclear artillery is a subset of limited-yield tactical nuclear weapons, in particular those weapons that are launched from the ground at battlefield targets... shell	beryllium-clad, require cleaning before long-term storage
LLNL	W55 W55 The W55 was an American thermonuclear warhead used as the warhead for the SUBROC antisubmarine rocket system. The W55 was designed in the early-1960s, and produced from 1964 to 1968. The last units were retired from service in 1990. A total of 285 W55 weapons were produced.The W55 had a yield...	MC1324	retired	UUM-44 SUBROC UUM-44 SUBROC The UUM-44 SUBROC was a type of submarine-launched rocket deployed by the United States Navy as an anti-submarine weapon.-Development:... antisubmarine missile	beryllium-clad?
LLNL	W56 W56 The W56 is an American thermonuclear warhead produced starting in 1963 which saw service until 1993, on the Minuteman I and II ICBMs.The W56 was manufactured in a series of models, all the same rough size and 1.2 megaton yield. The Mod-1, Mod-2, and Mod-3 variants weighed 600 pounds, with the...	MC1801	retired	Minuteman I, Minuteman II	high radiation, require cleaning before long-term storage
LLNL	W68 W68 The W68 warhead was the warhead used on the UGM-73 Poseidon SLBM missile. It was developed in the late 1960s at Lawrence Livermore National Laboratory.-Specifications:The W68 weighs...	MC1978	retired	UGM-73 Poseidon UGM-73 Poseidon The Poseidon missile was the second US Navy ballistic missile system, powered by a two-stage solid fuel rocket. It succeeded the Polaris missile beginning in 1972, bringing major advances in warheads and accuracy... SLBM
LLNL	W70 W70 W70 is the designation for a tactical nuclear warhead developed by the United States in the early 1970s. The Lawrence Livermore National Laboratory designed W70 was used on the MGM-52 Lance. About 1250 were built in total. The warhead had a variable yield of between 1 and 100 kilotons, selectable... -0	MC2381	retired	MGM-52 Lance
LLNL	W70 W70 W70 is the designation for a tactical nuclear warhead developed by the United States in the early 1970s. The Lawrence Livermore National Laboratory designed W70 was used on the MGM-52 Lance. About 1250 were built in total. The warhead had a variable yield of between 1 and 100 kilotons, selectable... -1	MC2381a	retired	MGM-52 Lance
LLNL	W70 W70 W70 is the designation for a tactical nuclear warhead developed by the United States in the early 1970s. The Lawrence Livermore National Laboratory designed W70 was used on the MGM-52 Lance. About 1250 were built in total. The warhead had a variable yield of between 1 and 100 kilotons, selectable... -2	MC2381b	retired	MGM-52 Lance
LLNL	W70 W70 W70 is the designation for a tactical nuclear warhead developed by the United States in the early 1970s. The Lawrence Livermore National Laboratory designed W70 was used on the MGM-52 Lance. About 1250 were built in total. The warhead had a variable yield of between 1 and 100 kilotons, selectable... -3	MC2381c	retired	MGM-52 Lance, enhanced-radiation Neutron bomb A neutron bomb or enhanced radiation weapon or weapon of reinforced radiation is a type of thermonuclear weapon designed specifically to release a large portion of its energy as energetic neutron radiation rather than explosive energy...
LLNL	W71 W71 The W-71 nuclear warhead was a US thermonuclear warhead developed at Lawrence Livermore National Laboratory in California and deployed on the LIM-49A Spartan Anti-ballistic missile...	?	retired	LIM-49 Spartan antiballistic missile	require cleaning before long-term storage
LLNL	W79 W79 The W79 was an American nuclear artillery shell, fired from any standard 8 inch howitzer e.g. the M115.The W79 was produced in two models, the "W79 Mod 0" and "W79 Mod 1"...	MC2574	retired	8" nuclear artillery Nuclear artillery Nuclear artillery is a subset of limited-yield tactical nuclear weapons, in particular those weapons that are launched from the ground at battlefield targets... shell	beryllium-clad?

Safety considerations

The first weapons had removable pits, which were installed into the bomb shortly before its deployment. The ongoing miniaturization process led to design changes, whereby the pit could be inserted in the factory during the device assembly. This necessitated safety testing to make sure that accidental detonation of the high explosives would not cause a full-scale nuclear explosion; Project 56

Project 56 (nuclear test)

Project 56 was a series of one-point safety tests conducted in Area 11 of the Nevada Test Site between 1955 and 1956.- Introduction :The purpose of these experiments was to determine whether a weapon or warhead damaged in an accident would detonate with a nuclear yield, even if some or all of the...

was one of such a series of tests.

Accidental high-yield detonation was always a concern. The levitated pit design made it practical to allow in-flight insertion of pits to the bombs, separating the fissile core from the explosives around it. Many cases of accidental bomb losses and explosions therefore led only to dispersal of uranium from the bomb's tamper. Later hollow-pit designs, where there is no space between the pit and the tamper, however, made this impossible.

The pits of earlier weapons had accessible inner cavities. For safety, objects were inserted into the pit and removed only when needed. Some larger pits, e.g. the British Green Grass, had their inner cavity lined with rubber and filled with metal balls; this design was improvised and far from optimal, for example in that subjecting the safed pit with balls inside to vibration, e.g. in an airplane, could lead to its damage. A fine metal chain from a neutron-absorbing material (the same used for reactor control rod

Control rod

A control rod is a rod made of chemical elements capable of absorbing many neutrons without fissioning themselves. They are used in nuclear reactors to control the rate of fission of uranium and plutonium...

s, e.g. cadmium

Cadmium

Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...

), can be used instead. The W47

W47

The W47 was an American thermonuclear warhead used on the Polaris A-1 sub-launched ballistic missile system. Various models were in service from 1960 through the end of 1974...

warhead had its pit filled with a cadmium-boron

Boron

wire when it was manufactured; on arming the weapon, the wire was pulled out to a spool by a small motor and could not be reinserted. However, the wire tended to become brittle and break during removal, making its complete removal impossible and rendering the warhead a dud.

The switch from solid to hollow pits caused a work safety issue; the larger surface-to-mass ratio led to comparatively higher emission of gamma rays and necessitated the installation of better radiation shielding in the Rocky Flats production facility. The increased amount of rolling and machining required led to higher consumption of machining oil and tetrachloromethane, used for degreasing the parts afterwards and creating a large amount of contaminated waste. The pyrophoric plutonium shavings also posed a risk of self-ignition.

Sealed pits require a different method of safing. Many techniques are used, including Permissive Action Link

Permissive Action Link

A Permissive Action Link is a security device for nuclear weapons. Its purpose is to prevent unauthorized arming or detonation of the nuclear weapon.The United States Department of Defense definition is:...

s and strong link weak link

Strong link weak link

A Strong link/weak link and Exclusion zone nuclear detonation mechanism is a type of safety mechanism employed in the arming and firing mechanisms of modern nuclear weapons. It is a form of automatic safety interlock...

systems, designed to fail in case of an accident or improper arming sequence; these include mechanical interlocks, critical parts designed to malfunction in case of fire or impact, etc.

Beryllium cladding, while advantageous technically, poses risk for the weapon plant employees. Machining the tamper shells produces beryllium and beryllium oxide

Beryllium oxide

Beryllium oxide , also known as beryllia, is an inorganic compound with the formula BeO. This colourless solid is a notable electrical insulator with a higher thermal conductivity than any other non-metal except diamond, and actually exceeds that of some metals. As an amorphous solid, beryllium...

dust; its inhalation can cause berylliosis

Berylliosis

Berylliosis, or chronic beryllium disease , is a chronic allergic-type lung response and chronic lung disease caused by exposure to beryllium and its compounds. As an occupational lung disease, it is most classically associated with beryllium mining or manufacturing of fluorescent light bulbs...

. By the 1996, the US Department of Energy identified more than 50 cases of chronic berylliosis among nuclear industry employees, including three dozen in the Rocky Flats Plant; several died.

After the 1966 Palomares B-52 crash and the 1968 Thule Air Base B-52 crash, the safety of weapons against accidental plutonium dispersal became a concern of US military.

Fire-resistant pits (FRP) are a safety feature of modern nuclear weapons, reducing plutonium dispersal in case of fire. The current pits are designed to contain molten plutonium in temperatures up to 1000°C, the approximate temperature of a burning aircraft fuel, for several hours. Fire-resistant pits would be of no help in cases where pits were scattered around by an explosion; they are used therefore together with insensitive high explosives, which should be resistant to accidental detonation by impact or fire, and undetonable propellants when used in missiles. Vanadium cladding was tested for design of fire-resistant pits, but it is unknown if it is in use or only experimental. The W87

W87

The W87 is an American thermonuclear missile warhead. It was created for use on the MX or Peacekeeper ICBM, 50 of which, with up to 12 warheads per missile, were deployed during the 1986-2005 period...

warhead is an example of a FRP-employing assembly. FRP does not, however, provide protection if the pit cladding is mechanically damaged, and may fail if subjected to missile fuel fire, which has a higher burning temperature (about 2000 °C) than does aircraft fuel. Severe weight and size constraints may preclude the use of both FRP and insensitive explosives. SLBMs, with their size considerations and more energetic and vulnerable fuel, tend to be less safe than ICBMs.

Other energetic material

Energetic material

Energetic materials are a class of material with high amount of stored chemical energy that can be released.Typical classes of energetic materials are e.g. explosives, pyrotechnic compositions, propellants , and fuels ....

s in the vicinity of the pit also influence its safety. US missile propellants come in two general classes. The class 1.3, fire hazard but very difficult to impossible to detonate; an example is 70% ammonium perchlorate

Ammonium perchlorate

Ammonium perchlorate is an inorganic compound with the formula NH4ClO4. It is the salt of perchloric acid and ammonia. It is a powerful oxidizer, which is why its main use is in solid propellants...

, 16% aluminium

Aluminium

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

, and 14% binder. The class 1.1, both fire and detonation hazard, is a double-base propellant based on cross-linked polymer, containing 52% HMX

HMX

HMX, also called octogen, is a powerful and relatively insensitive nitroamine high explosive, chemically related to RDX. Like RDX, the name has been variously listed as High Melting eXplosive, Her Majesty's eXplosive, High-velocity Military eXplosive, or High-Molecular-weight rdX.The molecular...

, 18% nitroglycerine, 18% aluminium, 4% ammonium perchlorate, and 8% binder. The 1.1 propellant has 4% higher specific impulse (about 270 s versus 260 s), giving an 8% longer range for constant burning time. The insensitive high explosives are also less powerful, necessitating larger and heavier warheads, which reduces the missile range - or sacrificing some yield. The safety/performance tradeoff is especially important for e.g. submarine

Submarine

A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

s. As of 1990, the Trident SLBMs used both detonable fuel and non-insensitive explosives.

Material considerations

Casting and then machining plutonium is difficult not only because of its toxicity, but because plutonium has many different metallic phase

Allotropes of plutonium

Even at ambient pressure, plutonium occurs in a variety of allotropes. These allotropes differ widely in crystal structure and density; the α and δ allotropes differ in density by more than 25% at constant pressure....

s, also known as allotropes. As plutonium cools, changes in phase result in distortion and cracking. This distortion is normally overcome by alloying it with 3–3.5 molar% (0.9–1.0% by weight) gallium

Gallium

Gallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...

, forming a plutonium-gallium alloy

Plutonium-gallium alloy

Plutonium-gallium alloy is an alloy of plutonium and gallium, used in nuclear weapon pits – the component of a nuclear weapon where the fission chain reaction is started....

, which causes it to take up its delta phase over a wide temperature range. When cooling from molten it then suffers only a single phase change, from epsilon to delta, instead of the four changes it would otherwise pass through. Other trivalent

Valence (chemistry)

In chemistry, valence, also known as valency or valence number, is a measure of the number of bonds formed by an atom of a given element. "Valence" can be defined as the number of valence bonds...

metals would also work, but gallium has a small neutron absorption cross section

Absorption cross section

Absorption cross section is a measure for the probability of an absorption process. More generally, the term cross section is used in physics to quantify the probability of a certain particle-particle interaction, e.g., scattering, electromagnetic absorption, etc...

and helps protect the plutonium against corrosion

Corrosion

. A drawback is that gallium compounds themselves are corrosive and so if the plutonium is recovered from dismantled weapons for conversion to plutonium dioxide

Plutonium dioxide

Plutonium oxide is the chemical compound with the formula PuO2. This high melting point solid is a principal compound of plutonium. It can vary in color from yellow to olive green, depending on the particle size, temperature and method of production....

for power reactor

Nuclear reactor

A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...

s, there is the difficulty of removing the gallium.

Because plutonium is chemically reactive it is common to plate the completed pit with a thin layer of inert metal, which also reduces the toxic hazard. The gadget used galvanic silver plating; afterwards, nickel

Nickel

Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

deposited from nickel tetracarbonyl vapors was used, but gold

Gold

Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...

is now preferred.

To produce the first pits, hot pressing

Hot pressing

was used to optimally employ the scarce plutonium. Later designs used machined

Machining

Conventional machining is a form of subtractive manufacturing, in which a collection of material-working processes utilizing power-driven machine tools, such as saws, lathes, milling machines, and drill presses, are used with a sharp cutting tool to physical remove material to achieve a desired...

pits, but turning

Turning

Turning is the process whereby a single point cutting tool is parallel to the surface. It can be done manually, in a traditional form of lathe, which frequently requires continuous supervision by the operator, or by using a computer controlled and automated lathe which does not. This type of...

produces a large amount of waste, both as pyrophoric turnings of plutonium and plutonium-contaminated oils and cutting fluid

Cutting fluid

Cutting fluid is a type of coolant and lubricant designed specifically for metalworking and machining processes. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, aerosols , and air or other gases. They may be made from petroleum distillates, animal...

s. The goal for the future is direct casting

Casting

In metalworking, casting involves pouring liquid metal into a mold, which contains a hollow cavity of the desired shape, and then allowing it to cool and solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process...

of the pit. In the absence of nuclear testing, however, the slightly different nature of cast and machined surfaces may cause difficult to predict performance differences.

Corrosion issues

Both uranium and plutonium are very susceptible to corrosion

Corrosion

. A number of the problem-plagued W47

W47

The W47 was an American thermonuclear warhead used on the Polaris A-1 sub-launched ballistic missile system. Various models were in service from 1960 through the end of 1974...

UGM-27 Polaris

The Polaris missile was a two-stage solid-fuel nuclear-armed submarine-launched ballistic missile built during the Cold War by Lockheed Corporation of California for the United States Navy....

warheads had to be replaced after corrosion of the fissile material was discovered during routine maintenance. The W58

W58

The W58 was an American thermonuclear warhead used on the Polaris A-3 submarine launched ballistic missile. Three W58 warheads were fitted as multiple warheads on each Polaris A-3 missile....

pits also suffered corrosion problems. The W45

W45

The W45 was a multipurpose American nuclear warhead developed in the early 1960s, first built in 1962 and fielded in some applications until 1988. It had a diameter of 11.5 inches , a length of 27 inches and weighed 150 pounds . The yields of different W45 versions were 0.5, 1, 5, 8, 10, and 15...

pit was prone to corrosion that could alter its geometry. The Green Grass pit was also corrosion-prone. The radioactivity of the materials used can also cause radiation corrosion in the surrounding materials. Plutonium is highly susceptible to humidity; moist air increases corrosion rate about 200 times. Hydrogen has strong catalytic effect on corrosion; its presence can accelerate corrosion rate by 13 orders of magnitude. Hydrogen can be generated from moisture and nearby organic materials (e.g. plastics) by radiolysis

Radiolysis

Radiolysis is the dissociation of molecules by nuclear radiation. It is the cleavage of one or several chemical bonds resulting from exposure to high-energy flux...

. These factors cause issues with storage of plutonium. The volume increase during oxidation can cause rupture of storage containers or deformation of pits.

Contamination of the pit with deuterium and tritium, whether accidental or if filled by design, can cause a hydride corrosion, which manifests as pitting corrosion

Pitting corrosion

Pitting corrosion, or pitting, is a form of extremely localized corrosion that leads to the creation of small holes in the metal. The driving power for pitting corrosion is the depassivation of a small area, which becomes anodic while an unknown but potentially vast area becomes cathodic, leading...

and a growth of a surface coating of pyrophoric plutonium hydride

Plutonium hydride

Plutonium hydride is the chemical compound with the formula PuH2. It is one of two characterised hydrides of plutonium, the other is PuH3. PuH2 is non-stoichiometric with a composition range of PuH2 – PuH2.7. Additionally metastable stoichiometries with an excess of hydrogen can be formed. PuH2...

. It also greatly accelerates the corrosion rates by atmospheric oxygen. Deuterium and tritium also cause hydrogen embrittlement

Hydrogen embrittlement

Hydrogen embrittlement is the process by which various metals, most importantly high-strength steel, become brittle and fracture following exposure to hydrogen...

in many materials.

Improper storage can promote corrosion of the pits. The AL-R8 containers used in the Pantex

Pantex

The Pantex plant is America's only nuclear weapons assembly and disassembly facility and is charged with maintaining the safety, security and reliability of the nation’s nuclear weapons stockpile. The facility is located on a 16,000 acre site 17 miles northeast of Amarillo, in Carson County,...

facility for storage of the pits are said to promote instead of hinder corrosion, and tend to corrode themselves. The decay heat released by the pits is also a concern; some pits in storage can reach temperatures as high as 150°C, and the storage facilities for larger numbers of pits may require active cooling. Humidity control can also present problems for pit storage.

Beryllium cladding can be corroded by some solvents used for cleaning of the pits. Research shown that trichloroethylene

Trichloroethylene

The chemical compound trichloroethylene is a chlorinated hydrocarbon commonly used as an industrial solvent. It is a clear non-flammable liquid with a sweet smell. It should not be confused with the similar 1,1,1-trichloroethane, which is commonly known as chlorothene.The IUPAC name is...

(TCE) causes beryllium corrosion, while trichloroethane

Trichloroethane

Trichloroethane can refer to either of two isomeric chemical compounds:* 1,1,1-Trichloroethane * 1,1,2-Trichloroethane...

(TCA) does not. Pitting corrosion

Pitting corrosion

of beryllium cladding is a significant concern during prolonged storage of pits in the Pantex

Pantex

facility.

Isotopic composition issues

The presence of plutonium-240

Plutonium-240

Plutonium-240 is an isotope of the metal plutonium formed when plutonium-239 captures a neutron. About 62% to 73% of the time when Pu-239 captures a neutron it undergoes fission; the rest of the time it forms Pu-240. The longer a nuclear fuel element remains in a nuclear reactor the greater the...

in the pit material causes increased production of heat and neutrons, impairs fission efficiency and increases the risk of predetonation and fizzle. Weapon-grade plutonium therefore has plutonium-240 content limited to less than 7%. Supergrade plutonium has less than 4% of the 240 isotope, and is used in systems where the radioactivity is a concern, e.g. in the US Navy weapons which have to share confined spaces on ships and submarines with the crews.

Plutonium-241

Plutonium-241

Plutonium-241 is an isotope of plutonium formed when plutonium-240 captures a neutron. Like Pu-239 but unlike 240Pu, 241Pu is fissile, with a neutron absorption cross section about 1/3 greater than 239Pu, and a similar probability of fissioning on neutron absorption, around 73%. In the non-fission...

, commonly comprising about 0.5% of weapon-grade plutonium, decays to americium-241, which is a powerful gamma radiation emitter. After several years, americium builds up in the plutonium metal, leading to increased gamma activity that poses occupational hazard for workers. Americium should therefore be separated, usually chemically, from newly produced and reprocessed plutonium. However in around 1967 the Rocky Flats Plant

Rocky Flats Plant

stopped this separation, blending up to 80% of old americium-containing pits directly to the foundry instead, in order to reduce costs and increase productivity; this led to higher exposition of workers to gamma radiation.

Production and inspections

The Radiation Identification System is among a number of methods developed for nuclear weapons inspections. It allows the fingerprinting of the nuclear weapons so that their identity and status can be verified. Various physics methods are used, including gamma spectroscopy

Gamma spectroscopy

Gamma-ray spectroscopy is the quantitative study of the energy spectra of gamma-ray sources, both nuclear laboratory, geochemical, and astrophysical. Gamma rays are the highest-energy form of electromagnetic radiation, being physically exactly like all other forms except for higher photon energy...

with high-resolution germanium

Germanium

Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. The isolated element is a semiconductor, with an appearance most similar to elemental silicon....

detectors. The 870.7 keV line in the spectrum, corresponding to the first excited state of oxygen-17

Oxygen-17

Oxygen-17 is a low abundant isotope of oxygen . Being the only stable isotope of oxygen possessing a nuclear spin and the unique characteristic of field-independent relaxation it enables NMR studies of metabolic pathways of compounds incorporating oxygen at high magnetic fields Oxygen-17 is a low...

, indicates the presence of plutonium(IV) oxide in the sample. The age of the plutonium can be established by measuring the ratio of plutonium-241

Plutonium-241

and its decay product, americium-241. However, even passive measurements of gamma spectrums may be a contentious issue in international weapon inspections, as it allows determination of e.g. the isotopic composition of plutonium, which can be considered a secret.

Between 1954 and 1989, pits for US weapons were produced at the Rocky Flats Plant

Rocky Flats Plant

; the plant was later closed due to numerous safety issues. The Department of Energy

United States Department of Energy

The United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...

attempted to restart pit production there, but repeatedly failed. In 1993, the DOE relocated beryllium

Beryllium

production operations from defunct Rocky Flats Plant to Los Alamos National Laboratory

Los Alamos National Laboratory

Los Alamos National Laboratory is a United States Department of Energy national laboratory, managed and operated by Los Alamos National Security , located in Los Alamos, New Mexico...

; in 1996 the pit production was also relocated there. The reserve and surplus pits, along with pits recovered from disassembled nuclear weapons, totalling over 12,000 pieces, are stored in the Pantex

Pantex

plant. 5,000 of them, comprising about 15 tons of plutonium, are designated as strategic reserve; the rest is surplus to be withdrawn. The current LANL production of new pits is limited to about 20 pits per year, though NNSA is pushing to increase the production, for the Reliable Replacement Warhead

Reliable Replacement Warhead

The Reliable Replacement Warhead was a proposed new American nuclear warhead design and bomb family that was intended to be simple, reliable and to provide a long-lasting, low maintenance future nuclear force for the United States...

program. The US Congress however has repeatedly declined funding.

Up until around 2010, Los Alamos National Laboratory had the capacity to produce 10 to 20 pits a year. The Chemistry and Metallurgy Research Replacement Facility

Chemistry and Metallurgy Research Replacement Facility

The Chemistry and Metallurgy Research Replacement Facility, usually referred to as the CMRR, is a facility under construction at Los Alamos National Laboratory in New Mexico which is part of the United States' nuclear stockpile stewardship program. The facility will replace the aging Chemistry and...

(CMMR) will expand this capability, but it is not known by how much. An Institute for Defense Analyses

Institute for Defense Analyses

The Institute for Defense Analyses is a non-profit corporation that administers three federally funded research and development centers to assist the United States government in addressing important national security issues, particularly those requiring scientific and technical expertise...

report written before 2008 estimated a “future pit production requirement of 125 per year at the CMRR, with a surge capability of 200."

Russia stores the material from decommissioned pits in the Mayak

Mayak

Mayak Production Association refers to an industrial complex that is one of the biggest nuclear facilities in the Russian Federation. It housed plutonium production reactors and a reprocessing plant...

facility.

Pit recycling

Recovery of plutonium from decommissioned pits can be achieved by numerous means, both mechanical (e.g. removal of cladding by a lathe

Lathe

) and chemical. A hydride method is commonly used; the pit is cut in half, a half of the pit is laid inside-down above a funnel and a crucible in a sealed apparatus, and an amount of hydrogen is injected into the space. The hydrogen reacts with the plutonium producing plutonium hydride

Plutonium hydride

, which falls to the funnel and the crucible, where it is melted while releasing the hydrogen. Plutonium can also be converted to a nitride or oxide. Practically all plutonium can be removed from a pit this way. The process is complicated by the wide variety of the constructions and alloy compositions of the pits, and the existence of composite uranium-plutonium pits. Weapons-grade plutonium must also be blended with other materials to alter its isotopic composition enough to hinder its reuse in weapons.

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