| Energy type | Proportion of total energy (%) | |
|---|---|---|
| Fission | Enhanced | |
| Blast | 50 | 40[1] to minimum 30[2] |
| Thermal energy | 35 | 25[1] to minimum 20[2] |
| Prompt radiation | 5 | 45 to minimum 30[1] |
| Residual radiation | 10 | 5[1] |
Aneutron bomb, officially defined as a type ofenhanced radiation weapon (ERW), is a low-yieldthermonuclear weapon designed to maximize lethalneutron radiation in the immediate vicinity of the blast while minimizing the physical power of the blast itself. The neutron release generated by anuclear fusion reaction is intentionally allowed to escape the weapon, rather than being absorbed by its other components.[3] The neutron burst, which is used as the primary destructive action of the warhead, is able to penetrate enemy armor more effectively than a conventional warhead, thus making it more lethal as a tactical weapon.
The concept was originally developed by the United States in the late 1950s and early 1960s. It was seen as a "cleaner" bomb for use against massedSoviet armored divisions. As these would be used over allied nations, notablyWest Germany, the reduced blast damage was seen as an important advantage.[4][5] During theCold War, China also developed a neutron bomb but refrained from deploying it on tactical delivery systems.[6]: 76
ERWs were first operationally deployed foranti-ballistic missiles (ABMs). In this role, the burst of neutrons would cause nearby warheads to undergo partial fission, preventing them from exploding properly. For this to work, the ABM would have to explode within approximately 100 metres (300 ft) of its target. The first example of such a system was theW66, used on theSprint missile used in the USNike-X system. It is believed the Soviet equivalent, theA-135's53T6 missile, uses a similar design.[7]
The weapon was once again proposed for tactical use by the United States in the 1970s and 1980s, and production of theW70 began for theMGM-52 Lance in 1981. This time, it led to protests as the growinganti-nuclear movement gained strength through this period. Opposition was so intense that European leaders refused to accept it on their territory. US PresidentRonald Reagan ordered the production of the W70-3, which remained in the US stockpile until they were retired in 1992. The last W70 was dismantled in February 1996.[8]
In a standard thermonuclear design, a smallfission bomb is placed close to a larger mass of thermonuclear fuel, usually lithium deuteride. The two components are then placed within a thickradiation case, usually made fromuranium,lead, or steel. The case traps the energy from the fission bomb for a brief period, allowing it to heat and compress the main thermonuclear fuel. The case is normally made ofdepleted uranium ornatural uranium metal, because the thermonuclear reactions give off extraordinarily large numbers of high-energyneutrons that can cause fission reactions in the casing material. These can add considerable energy to the reaction; in a typical design, as much as 50% of the total energy comes from fission events in the casing. For this reason, these weapons are technically known as fission-fusion-fission designs.
In a neutron bomb, the casing material is selected either to be transparent to neutrons or to actively enhance their production. The burst of neutrons created in the thermonuclear reaction is then free to escape the bomb, outpacing the physical explosion. By designing the thermonuclear stage of the weapon carefully, the neutron burst can be maximized while minimizing the blast itself. This makes the lethal radius of the neutron burst greater than that of the explosion itself. Since the neutrons are absorbed or decay rapidly, such a burst over an enemy column would kill the crews but leave the area able to be quickly reoccupied.
Compared to a purefission bomb with an identical explosive yield, a neutron bomb would emit about ten times[9] the amount of neutron radiation. In a fission bomb, at sea level, the total radiation pulse energy which is composed of bothgamma rays and neutrons is approximately 5% of the entire energy released; in neutron bombs, it would be closer to 40%, with the percentage increase coming from the higher production of neutrons. Furthermore, the neutrons emitted by a neutron bomb have a much higher average energy level (close to 14 MeV) than those released during a fission reaction (1–2 MeV).[10]
Technically speaking, every low-yield nuclear weapon is a radiation weapon, including non-enhanced variants. All nuclear weapons up to about 10 kilotons in yield have prompt neutron radiation[2] as their furthest-reaching lethal component. For standard weapons above about 10 kilotons of yield, the lethal blast and thermal effects radius begins to exceed the lethalionizing radiation radius.[11][12][13] Enhanced radiation weapons also fall into this same yield range and simply enhance the intensity and range of the neutron dose for a given yield.
The conception of neutron bombs is generally credited toSamuel T. Cohen of theLawrence Livermore National Laboratory, who developed the concept in 1958.[14] Initial development was carried out as part of projects Dove and Starling, and an early device was tested underground in early 1962. Designs for a "weaponized" version were developed in 1963.[15][16]
Development of two production designs for the Army'sMGM-52 Lance short-range missile began in July 1964, theW63 at Livermore and theW64 atLos Alamos. Both entered phase three testing in July 1964, and the W64 was cancelled in favor of the W63 in September 1964. The W63 was in turn cancelled in November 1965 in favor of theW70 (Mod 0), a conventional design.[15] By this time, the same concepts were being used to develop warheads for theSprint missile, ananti-ballistic missile (ABM), with Livermore designing theW65 and Los Alamos theW66. Both entered phase three testing in October 1965, but the W65 was cancelled in favor of the W66 in November 1968. Testing of the W66 was carried out in the late 1960s, and it entered production in June 1974,[15] the first neutron bomb to do so. Approximately 120 were built, with about 70 of these being on active duty during 1975 and 1976 as part of theSafeguard Program. When that program was shut down they were placed in storage, and eventually decommissioned in the early 1980s.[15]
Development of ER warheads for Lance continued, but in the early 1970s, attention had turned to using modified versions of the W70, the W70 Mod 3.[15] Development was subsequently postponed by PresidentJimmy Carter in 1978 following protests against his administration's plans to deploy neutron warheads to ground forces in Europe.[17] OnNovember 17, 1978, in a test, theUSSR detonated its first similar-type bomb.[citation needed] PresidentRonald Reagan restarted production in 1981.[17] The Soviet Union renewed apropaganda campaign against the US's neutron bomb in 1981 following Reagan's announcement. In 1983, Reagan then announced theStrategic Defense Initiative, which surpassed neutron bomb production in ambition and vision and with that, neutron bombs quickly faded from the center of the public's attention.[citation needed]
| Initial | Enhanced | Gun caliber |
|---|---|---|
| W48 | W82 | 155 mm |
| W33 | W79 | 203mm |
Three types of enhanced radiation weapons (ERW) were deployed by the United States.[18] The W66 warhead, for the anti-ICBM Sprint missile system, was deployed in 1975 and retired the next year, along with the missile system. The W70 Mod 3 warhead was developed for the short-range, tactical MGM-52 Lance missile, and theW79 Mod 0 was developed fornuclear artillery shells. The latter two types were retired by PresidentGeorge H. W. Bush in 1992, following the end of theCold War.[19][20] The last W70 Mod 3 warhead was dismantled in 1996,[citation needed] and the last W79 Mod 0 was dismantled by 2003, when the dismantling of all W79 variants was completed.[21]
According to theCox Report, as of 1999, the United States had never deployed a neutron weapon. The nature of this statement is not clear; it reads, "The stolen information also includes classified design information for an enhanced radiation weapon (commonly known as the "neutron bomb"), which neither the United States, nor any other nation, has ever deployed."[22] However, the fact that neutron bombs had been produced by the US was well known at this time and part of the public record. Cohen suggests the report is playing with the definitions; while the US bombs were never deployedto Europe, they remained stockpiled in the US.[23]
In addition to the two superpowers, France and China are known to have tested neutron or enhanced radiation bombs. France conducted an early test of the technology in 1967[24] and tested an actual neutron bomb in 1980.[25] China conducted a successful test of neutron bomb principles in 1984 and a successful test of a neutron bomb in 1988. However, neither of those countries chose to deploy neutron bombs. Chinese nuclear scientists stated before the 1988 test that China had no need for neutron bombs, but it was developed to serve as a "technology reserve", in case the need arose in the future.[26]
In May 1998, Senior Pakistani Scientist, Dr. N. M. Butt, stated that "PAEC built a sufficient number of neutron bombs—a battlefield weapon that is essentially a low yield device".[27]
In August 1999, the Indian government stated that India was capable of producing a neutron bomb.[28]
Although no country is currently known to deploy them in an offensive manner, all thermonucleardial-a-yield warheads that have about 10 kiloton and lower as one dial option, with a considerable fraction of that yield derived from fusion reactions, can be considered able to be neutron bombs in use, if not in name. The only country definitely known to deploy dedicated (that is, not dial-a-yield) neutron warheads for any length of time is the Soviet Union/Russia,[7] which inherited the USSR's neutron warhead equippedABM-3 Gazelle missile program. This ABM system contains at least 68 neutron warheads with a 10-kiloton yield each and it has been in service since 1995, with inert missile testing approximately every other year since then (2014). The system is designed to destroy incoming endoatmospheric nuclear warheads aimed atMoscow and other targets and is the lower-tier/last umbrella of theA-135 anti-ballistic missile system (NATO reporting name: ABM-3).[citation needed]
By 1984, according toMordechai Vanunu, Israel was mass-producing neutron bombs.[29]
Considerable controversy arose in the US and Western Europe following a June 1977Washington Post exposé describing US government plans to equip US Armed Forces with neutron bombs. The article focused on the fact that it was the first weapon specifically intended to kill humans with radiation.[30][31] Lawrence Livermore National Laboratory directorHarold Brown and Soviet General SecretaryLeonid Brezhnev both described neutron bombs as a "capitalist bomb", because it was designed to destroy people while preserving property.[32][33][need quotation to verify]
Neutron bombs are purposely designed with explosive yields lower than other nuclear weapons. Since neutrons are scattered and absorbed by air,[2] neutron radiation effects drop off rapidly with distance in air. As such, there is a sharper distinction, relative to thermal effects, between areas of high lethality and areas with minimal radiation doses.[3] No high yield (more than c. 10 kiloton) nuclear bombs, including the extreme example of the 50megatonTsar Bomba, are able to radiate sufficient neutrons beyond their lethal blast range when detonated as a surface burst or low altitudeair burst and so are not classified as neutron bombs, thus limiting the yield of neutron bombs to a maximum of about 10 kilotons. The intensepulse of high-energy neutrons generated by a neutron bomb is the principal killing mechanism, not the fallout, heat or blast.
The inventor of the neutron bomb, Sam Cohen, criticized the description of the W70 as a neutron bomb since it could be configured to yield 100 kilotons:
the W-70 ... is not even remotely a "neutron bomb." Instead of being the type of weapon that, in the popular mind, "kills people and spares buildings" it is one that both kills and physically destroys on a massive scale. The W-70 is not a discriminate weapon, like the neutron bomb—which, incidentally, should be considered a weapon that "kills enemy personnel while sparing the physical fabric of the attacked populace, and even the populace too."[36]
Although neutron bombs are commonly believed to "leave the infrastructure intact", with current designs that have explosive yields in the low kiloton range,[37] detonation in (or above) a built-up area would still cause a sizable degree of building destruction, through blast and heat effects out to a moderate radius, albeit considerably less destruction, than when compared to a standard nuclear bomb of theexact same total energy release or "yield".[38]
TheWarsaw Pact tank strength was over twice that of NATO, andSoviet deep battle doctrine was likely to be to use this numerical advantage to rapidly sweep across continental Europe if the Cold War ever turned hot. Any weapon that could break up their intended mass tank formation deployments and force them to deploy their tanks in a thinner, moreeasily dividable manner,[4] would aid ground forces in the task of hunting down solitary tanks and usinganti-tank missiles against them,[41] such as the contemporaryM47 Dragon andBGM-71 TOW missiles, of which NATO had hundreds of thousands.[4]
Rather than making extensive preparations for battlefield nuclear combat in Central Europe, the Soviet military leadership believed that conventional superiority provided the Warsaw Pact with the means to approximate the effects of nuclear weapons and achieve victory in Europe without resort to those weapons.[42]
Neutron bombs, or more precisely, enhanced [neutron] radiation weapons were also to find use as strategic anti-ballistic missile weapons,[38] and in this role, they are believed to remain in active service within Russia's Gazelle missile.[7]
Upon detonation, a near-groundairburst of a 1-kiloton neutron bomb would produce a large blast wave and a powerful pulse of both thermal radiation andionizing radiation in the form of fast (14.1 MeV) neutrons. The thermal pulse would causethird degree burns to unprotected skin out to approximately 500 meters. The blast would create pressures of at least 4.6 psi (32 kPa) out to a radius of 600 meters, which would severely damage all non-reinforced concrete structures. At the conventional effective combat range against modernmain battle tanks andarmored personnel carriers (< 690–900 m), the blast from a 1 kt neutron bomb would destroy or damage to the point of nonusability almost all un-reinforced civilian buildings.[citation needed]
Using neutron bombs to stop an enemy armored attack by rapidly incapacitating crews with a dose of 80+Gy of radiation[43] would require exploding large numbers of them to blanket the enemy forces, destroying all normal civilian buildings within c. 600 meters of the immediate area.[43][44]Neutron activation from the explosions could make many building materials in the city radioactive, such asgalvanized steel (seearea denial use below).
Because liquid-filled objects like the human body are resistant to gross overpressure, the 4–5 psi (28-34 kPa) blastoverpressure would cause very few direct casualties at a range of c. 600 m. The powerful winds produced by this overpressure, however, could throw bodies into objects or throw debris at high velocity, including window glass, both with potentially lethal results. Casualties would be highly variable depending on surroundings, including potential building collapses.[45]
The pulse of neutron radiation would cause immediate and permanent incapacitation to unprotected outdoor humans in the open out to 900 meters,[9] with death occurring in one or two days. Themedian lethal dose (LD50) of 6 Gray would extend to between 1350 and 1400 meters for those unprotected and outdoors,[43] where approximately half of those exposed would die of radiation sickness after several weeks.
A human residing within, or simply shielded by, at least one concrete building with walls and ceilings 30 cm (12 in) thick, or alternatively of dampsoil 24 inches (60 cm) thick, would receive a neutron radiation exposure reduced by a factor of 10.[46] Even near ground zero, basement sheltering or buildings with similar radiation shielding characteristics would drastically reduce the radiation dose.[4]
Furthermore, theneutron absorption spectrum of air is disputed by some authorities, and depends in part on absorption byhydrogen fromwater vapor. Thus, absorption might vary exponentially with humidity, making neutron bombs far more deadly indesert climates than in humid ones.[43]
The questionable effectiveness of ER weapons against modern tanks is cited as one of the main reasons that these weapons are no longer fielded orstockpiled. With the increase in average tank armor thickness since the first ER weapons were fielded, it was argued in the March 13, 1986,New Scientist magazine that tank armor protection was approaching the level where tank crews would be almost fully protected from radiation effects. Thus, for an ER weapon to incapacitate a modern tank crew through irradiation, the weapon must be detonated at such proximity to the tank that thenuclear explosion's blast would now be equally effective at incapacitating it and its crew.[47]
However, although the author did note that effectiveneutron absorbers andneutron poisons such asboron carbide can be incorporated into conventional armor and strap-onneutron moderating hydrogenous material (substances containing hydrogen atoms), such as explosivereactive armor, increasing the protection factor, the author holds that in practice, combined withneutron scattering, the actual average total tank area protection factor is rarely higher than 15.5 to 35.[48] According to theFederation of American Scientists, the neutron protection factor of a "tank" can be as low as 2,[2] without qualifying whether the statement implies alight tank,medium tank, ormain battle tank.
A compositehigh-density concrete, or alternatively, a laminatedgraded-Z shield, 24 units thick of which 16 units are iron and 8 units arepolyethylene containing boron (BPE), and additional mass behind it to attenuate neutron capture gamma rays, is more effective than just 24 units of pure iron or BPE alone, due to the advantages of both iron and BPE in combination. Duringneutron transport, iron is effective in slowing down/scattering high-energy neutrons in the 14-MeV energy range and attenuating gamma rays, while the hydrogen in polyethylene is effective in slowing down these now slowerfast neutrons in the few MeV range, and boron 10 has a high absorption cross section forthermal neutrons and a low production yield of gamma rays when it absorbs a neutron.[49][50][51] The SovietT-72 tank, in response to the neutron bomb threat, is cited as having fitted a boronated[52] polyethylene liner, which has had its neutron shielding properties simulated.[46][53]
However, some tank armor material containsdepleted uranium (DU), common in the US'sM1A1 Abrams tank, which incorporates steel-encased depleted uranium armor,[54] a substance that will fast fission when itcaptures a fast, fusion-generated neutron, and thus on fissioning will producefission neutrons andfission products embedded within the armor, products which emit, among other things, penetrating gamma rays. Although the neutrons emitted by the neutron bomb may not penetrate to the tank crew in lethal quantities, the fast fission of DU within the armor could still ensure a lethal environment for the crew and maintenance personnel by fission neutron and gamma ray exposure[dubious –discuss],[55][unreliable source?] largely depending on the exact thickness and elemental composition of the armor—information usually hard to attain. Despite this,Ducrete—which has an elemental composition similar (but not identical) to the ceramicsecond-generation heavy metal Chobham armor of the Abrams tank—is an effective radiation shield, to bothfission neutrons and gamma rays due to it being a graded-Z material.[56][57] Uranium, being about twice as dense as lead, is thus nearly twice as effective at shielding gamma ray radiation per unit thickness.[58]
As an anti-ballistic missile weapon, the first fielded ER warhead, the W66, was developed for the Sprint missile system as part of the Safeguard Program to protect United States cities andmissile silos from incoming Soviet warheads.
A problem faced by Sprint and similar ABMs was that the blast effects of their warheads change greatly as they climb and the atmosphere thins out. At higher altitudes, starting around 60,000 feet (18,000 m) and above, the blast effects begin to drop off rapidly as the air density becomes very low. This can be countered by using a larger warhead, but then it becomes too powerful when used at lower altitudes. An ideal system would use a mechanism that was less sensitive to changes in air density.
Neutron-based attacks offer one solution to this problem. The burst of neutrons released by an ER weapon can induce fission in the fissile materials of primary in the target warhead. The energy released by these reactions may be enough to melt the warhead, but even at lower fission rates, the "burning up" of some of the fuel in the primary can cause it to fail to explode properly, or "fizzle".[59] Thus, a small ER warhead can be effective across a wide altitude band, using blast effects at lower altitudes and the increasingly long-ranged neutrons as the engagement rises.
The use of neutron-based attacks was discussed as early as the 1950s, with the USAtomic Energy Commission mentioning weapons with a "clean, enhanced neutron output" for use as "antimissile defensive warheads."[60] Studying, improving and defending against such attacks was a major area of research during the 1950s and '60s. A particular example of this is the USPolaris A-3 missile, which delivered three warheads travelling on roughly the same trajectory, and thus with a short distance between them. A single ABM could conceivably destroy all three through neutron flux. Developing warheads that were less sensitive to these attacks was also a major area of research in the US and UK during the 1960s.[59]
Some sources claim that the neutron flux attack was also the main design goal of the various nuclear-tipped anti-aircraft weapons like theAIM-26 Falcon andCIM-10 Bomarc. OneF-102 pilot noted:
GAR-11/AIM-26 was primarily a weapon-killer. The bomber(s, if any) was collateral damage. The weapon was proximity-fused to ensure detonation close enough so an intense flood of neutrons would result in an instantaneous nuclear reaction (NOT full-scale) in the enemy weapon's pit; rendering it incapable of functioning as designed ... [O]ur first "neutron bombs" were the GAR-11 and MB-1 Genie.[60]
It has also been suggested that neutron flux's effects on the warhead electronics are another attack vector for ER warheads in the ABM role.Ionization greater than 50Gray insilicon chips delivered over seconds to minutes will degrade the function ofsemiconductors for long periods.[61] However, while such attacks might be useful against guidance systems, which used relatively advanced electronics, in the ABM role, these components have long ago separated from the warheads by the time they come within range of the interceptors. The electronics in the warheads themselves tend to be very simple, and hardening them was one of the many issues studied in the 1960s.[59]
Lithium-6 hydride (Li6H) is cited as being used as a countermeasure to reduce the vulnerability and "harden" nuclear warheads from the effects of externally generated neutrons.[62][63]Radiation hardening of the warhead's electronic components as a countermeasure to high altitude neutron warheads somewhat reduces the range that a neutron warhead could successfully cause an unrecoverableglitch by thetransient radiation effects on electronics (TREE) effects.[64][65]
At very high altitudes, at the edge of the atmosphere and above it, another effect comes into play. At lower altitudes, theX-rays generated by the bomb are absorbed by the air and havemean free paths on the order of meters. But as the air thins out, the X-rays can travel further, eventually outpacing the area of effect of the neutrons. Inexoatmospheric explosions, this can be on the order of 10 kilometres (6.2 mi) in radius. In this sort of attack, it is the X-rays promptly delivering energy on the warhead surface that is the active mechanism; the rapid ablation (or "blowoff") of the surface creates shock waves that can break up the warhead.[66]
In November 2012, British Labour peerLord Gilbert suggested that multiple enhanced radiation reduced blast (ERRB) warheads could be detonated in the mountain region of the Afghanistan-Pakistan border to prevent infiltration.[67] He proposed to warn the inhabitants to evacuate, then irradiate the area, making it unusable and impassable.[68] Used in this manner, the neutron bomb(s), regardless of burst height, would releaseneutron activated casing materials used in the bomb, and depending on burst height, create radioactive soilactivation products.
In much the same fashion as thearea denial effect resulting from fission product (the substances that make up mostfallout) contamination in an area following a conventionalsurface-burst nuclear explosion, as considered in the Korean War byDouglas MacArthur, it would thus be a form ofradiological warfare—with the difference that neutron bombs produce half, or less, of the quantity of fission products relative to the same-yield purefission bomb. Radiological warfare with neutron bombs that rely onfission primaries would thus still produce fission fallout, albeit a comparativelycleaner and shorter-lasting version of it in the area than if air bursts were used, as little to no fission products would be deposited on the direct immediate area, instead becoming diluted globalfallout.
A militarily useful use of a neutron bomb with respect to area denial would be to encase it in a thick shell of material that could be neutron activated, and use a surface burst. In this manner, the neutron bomb would be turned into asalted bomb; for example,zinc-64, produced as a byproduct ofdepleted zinc oxide enrichment, would when neutron activated become zinc-65, which is a gamma emitter with ahalf-life of 244 days.[70][improper synthesis?]
With considerable overlap between the two devices, the prompt radiation effects of apure fusion weapon would similarly be much higher than that of a pure-fission device: approximately twice the initial radiation output of current standard fission–fusion-based weapons. In common with all neutron bombs that must presently derive a small percentage of trigger energy from fission, in any given yield, a 100% pure fusion bomb would likewise generate a smaller atmospheric blast wave than apure-fission bomb. The latter fission device has a higher kinetic energy-ratio per unit of reaction energy released, which is most notable in the comparison with the D-T fusion reaction. A larger percentage of the energy from a D-T fusion reaction is inherently put into uncharged neutron generation as opposed to charged particles, such as thealpha particle of the D-T reaction, the primary species, that is most responsible for thecoulomb explosion/fireball.[71]
Anti-ballistic missile warheads
Ballistic missile warheads
Artillery
{{cite web}}:|author= has generic name (help){{cite book}}:|first1= has generic name (help)[permanent dead link]{{cite book}}:|first1= has generic name (help)[permanent dead link]{{cite web}}: CS1 maint: archived copy as title (link) Paper Summary Submitted to Spectrum 2000, Sept 24-28, 2000, Chattanooga, TN. Ducrete: A Cost Effective Radiation Shielding Material. Quote- "The Ducrete/DUAGG replaces the conventional aggregate in concrete producing concrete with a density of 5.6 to 6.4 g/cm3 (compared to 2.3 g/cm3 for conventional concrete). This shielding material has the unique feature of having both high Z and low Z elements in a single matrix. Consequently, it is very effective for the attenuation of gamma and neutron radiation ..."{{cite magazine}}:Cite magazine requires|magazine= (help)Due to moderating ability and light weight, used to harden weapons against outside neutron fluxes (especially in combination with Li-6) ...The very high cross section of this reaction for thermalized neutrons, combined with the light weight of the Li-6 atom, make it useful in the form of lithium hydride for hardening of nuclear weapons against external neutron fluxes.
The fact that Li6H is used in unspecified weapons for hardening
Nuclear weapon-generated X-rays are the chief threat to the survival of strategic missiles in-flight above the atmosphere and to satellites ... The Neutron and gamma ray effects dominate at lower altitudes where the air absorbs most of the X-rays.
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