Neutron bomb

From Wikipedia, the free encyclopedia

A neutron bomb, officially defined as a type of enhanced radiation weapon (ERW), is a low yield thermonuclear weapon designed to maximize lethal neutron radiation in the immediate vicinity of the blast while minimizing the physical power of the blast itself. The neutron release generated by a nuclear fusion reaction is intentionally allowed to escape the weapon, rather than being absorbed by its other components. 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 US in the late 1950s and early 1960s. It was seen as a "cleaner" bomb for use against massed Soviet armored divisions. As these would be used over allied nations, notably West Germany, the reduced blast damage was seen as an important advantage.

ERWs were first operationally deployed for anti-ballistic missiles (ABM). 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 ca. 100 metres (300 ft) of its target. The first example of such a system was the W66, used on the Sprint missile used in the US's Nike-X system. It is believed the Soviet equivalent, the A-135's 53T6 missile, uses a similar design.

The weapon was once again proposed for tactical use by the US in the 1970s and 1980s, and production of the W70 began for the MGM-52 Lance in 1981. This time it experienced a firestorm of protest as the growing anti-nuclear movement gained strength through this period. Opposition was so intense that European leaders refused to accept it on their territory. President Ronald Reagan bowed to pressure and the built examples of the W70-3 remained stockpiled in the US until they were retired in 1992. The last W70 was dismantled in 2011.

Basic concept

In a standard thermonuclear design, a small fission bomb is placed close to a larger mass of thermonuclear fuel. The two components are then placed within a thick radiation case, usually made from uranium, 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 of depleted uranium or natural uranium metal, because the thermonuclear reactions give off massive numbers of high-energy neutrons 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 disappear from the environment rapidly, such a burst over an enemy column would kill the crews and leave the area able to be quickly reoccupied. 

Compared to a pure fission bomb with an identical explosive yield, a neutron bomb would emit about ten times the amount of neutron radiation. In a fission bomb, at sea level, the total radiation pulse energy which is composed of both gamma 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).

Technically speaking, every low yield nuclear weapon is a radiation weapon, including non-enhanced variants. Up to about 10 kilotons in yield, all nuclear weapons have prompt neutron radiation as their furthest-reaching lethal component, after which yield in regular nuclear weapons, the lethal blast and thermal effects radius begins to out-range the lethal ionizing radiation radius. 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.

History and deployment to present

The conception of neutron bombs is generally credited to Samuel T. Cohen of the Lawrence Livermore National Laboratory, who developed the concept in 1958. Initial development was carried out as part of projects Dove and Starling, and an early device was tested underground in early 1962. Designs of a "weaponized" version were carried out in 1963.

Development of two production designs for the army's MGM-52 Lance short-range missile began in July 1964, the W63 at Livermore and the W64 at Los 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 the W70 (Mod 0), a conventional design. By this time, the same concepts were being used to develop warheads for the Sprint missile, an anti-ballistic missile (ABM), with Livermore designing the W65 and Los Alamos the W66. 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 entered production in June 1974, 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 the Safeguard Program. When that program was shut down they were placed in storage, and eventually decommissioned in the early 1980s.

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. Development was subsequently postponed by President Jimmy Carter in 1978 following protests against his administration's plans to deploy neutron warheads to ground forces in Europe. On November 17, 1978, in a test the USSR detonated its first similar-type bomb. President Ronald Reagan restarted production in 1981. The Soviet Union renewed a propaganda campaign against the US's neutron bomb in 1981 following Reagan's announcement. In 1983 Reagan then announced the Strategic 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.

Three types of enhanced radiation weapons (ERW) were deployed by the United States. 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 the W79 Mod 0 was developed for nuclear artillery shells. The latter two types were retired by President George H. W. Bush in 1992, following the end of the Cold War. The last W70 Mod 3 warhead was dismantled in 1996, and the last W79 Mod 0 was dismantled by 2003, when the dismantling of all W79 variants was completed.

According to the Cox 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." 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 deployed to Europe, they remained stockpiled in the US.

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 and tested an "actual" neutron bomb in 1980. 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.

In August, 1999, the Indian government disclosed that India was capable of producing a neutron bomb.

Although no country is currently known to deploy them in an offensive manner, all thermonuclear dial-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, which inherited the USSR's neutron warhead equipped ABM-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 level nuclear warheads aimed at Moscow and other targets and is the lower-tier/last umbrella of the A-135 anti-ballistic missile system (NATO reporting name: ABM-3).

By 1984, according to Mordechai Vanunu, Israel was mass-producing neutron bombs.

Considerable controversy arose in the US and Western Europe following a June 1977 Washington Post exposé describing US government plans to purchase the bomb. The article focused on the fact that it was the first weapon specifically intended to kill humans with radiation. Lawrence Livermore National Laboratory director Harold Brown and Soviet General Secretary Leonid Brezhnev both described neutron bombs as a "capitalist bomb", because it was designed to destroy people while preserving property.

Use

The 1979 Soviet/Warsaw Pact invasion plan, "Seven Days to the River Rhine" to seize West Germany. Soviet analysts had correctly assumed that the NATO response would be to use regular tactical nuclear weapons to stop such a massive Warsaw Pact invasion. According to proponents, neutron bombs would blunt an invasion by Soviet tanks and armored vehicles without causing as much damage or civilian deaths as the older nuclear weapons would. Neutron bombs would have been used if the REFORGER conventional response of NATO to the invasion was too slow or ineffective.

 

Neutron bombs are purposely designed with explosive yields lower than other nuclear weapons. Since neutrons are scattered and absorbed by air, 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. All high yield (more than c. 10 kiloton) nuclear bombs, such as the extreme example of a device that derived 97% of its energy from fusion, the 50 megaton Tsar Bomba, are not able to radiate sufficient neutrons beyond their lethal blast range when detonated as a surface burst or low altitude air burst and so are no longer classified as neutron bombs, thus limiting the yield of neutron bombs to a maximum of about 10 kilotons. The intense pulse 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."

Although neutron bombs are commonly believed to "leave the infrastructure intact", with current designs that have explosive yields in the low kiloton range, 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 the exact same total energy release or "yield".

U.S. Army M110 howitzers in a 1984 REFORGER staging area before transport. Variants of this "dual capable" nuclear artillery howitzer would launch the W79 neutron bomb.

 

The Warsaw Pact tank strength was over twice that of NATO, and Soviet 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, more easily dividable manner, would aid ground forces in the task of hunting down solitary tanks and using anti-tank missiles against them, such as the contemporary M47 Dragon and BGM-71 TOW missiles, of which NATO had hundreds of thousands.

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."

Neutron bombs, or more precisely, enhanced [neutron] radiation weapons were also to find use as strategic anti-ballistic missile weapons, and in this role they are believed to remain in active service within Russia's Gazelle missile.

Effects

Wood frame house in 1953 nuclear test, 5 pounds per square inch (psi) overpressure, full collapse.

 

Upon detonation, a near-ground airburst of a 1 kiloton neutron bomb would produce a large blast wave and a powerful pulse of both thermal radiation and ionizing radiation, and non-ionizing radiation in the form of fast (14.1 MeV) neutrons. The thermal pulse would cause third degree burns to unprotected skin out to approximately 500 meters. The blast would create pressures of at least 4.6 psi out to a radius of 600 meters, which would severely damage all non-reinforced concrete structures. At the conventional effective combat range against modern main battle tanks and armored 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.

Using neutron bombs to stop an enemy armored attack by rapidly incapacitating crews with a dose of 8000+ rads of radiation 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. Neutron activation from the explosions could make many building materials in the city radioactive, such as zinc coated steel/galvanized steel (see area denial use below). 

Because liquid-filled objects like the human body are resistant to gross overpressure, the 4–5 psi blast overpressure 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.

The pulse of neutron radiation would cause immediate and permanent incapacitation to unprotected outdoor humans in the open out to 900 meters, with death occurring in one or two days. The median lethal dose (LD₅₀) of 600 rads would extend to between 1350 and 1400 meters for those unprotected and outdoors, 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 damp soil 24 inches thick, would receive a neutron radiation exposure reduced by a factor of 10. Even near ground zero, basement sheltering or buildings with similar radiation shielding characteristics would drastically reduce the radiation dose.

Furthermore, the neutron absorption spectrum of air is disputed by some authorities, and depends in part on absorption by hydrogen from water vapor. Thus, absorption might vary exponentially with humidity, making neutron bombs far more deadly in desert climates than in humid ones.

Effectiveness in modern anti-tank role

The neutron cross section and absorption probability in barns of the two natural boron isotopes found in nature (top curve is for 10 B and bottom curve for 11 B. As neutron energy increases to 14 MeV, the absorption effectiveness, in general, decreases. Thus, for boron-containing armor to be effective, fast neutrons must first be slowed by another element by neutron scattering.

 

The questionable effectiveness of ER weapons against modern tanks is cited as one of the main reasons that these weapons are no longer fielded or stockpiled. 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 the nuclear explosion's blast would now be equally effective at incapacitating it and its crew. However this assertion was regarded as dubious in the 12 June, 1986 New Scientist reply by C.S. Grace, a member of the Royal Military College of Science, as neutron radiation from a 1 kiloton neutron bomb would incapacitate the crew of a tank with a protection factor of 35 out to a range of 280 meters, but the incapacitating blast range, depending on the exact weight of the tank, is much less, from 70 to 130 meters. However although the author did note that effective neutron absorbers and neutron poisons such as boron carbide can be incorporated into conventional armor and strap-on neutron moderating hydrogenous material (substances containing hydrogen atoms), such as explosive reactive armor, can both increase the protection factor, the author holds that in practice combined with neutron scattering, the actual average total tank area protection factor is rarely higher than 15.5 to 35. According to the Federation of American Scientists, the neutron protection factor of a "tank" can be as low as 2, without qualifying whether the statement implies a light tank, medium tank, or main battle tank. 

A composite high density concrete, or alternatively, a laminated graded-Z shield, 24 units thick of which 16 units are iron and 8 units are polyethylene 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. During Neutron 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 slower fast neutrons in the few MeV range, and boron 10 has a high absorption cross section for thermal neutrons and a low production yield of gamma rays when it absorbs a neutron. The Soviet T72 tank, in response to the neutron bomb threat, is cited as having fitted a boronated polyethylene liner, which has had its neutron shielding properties simulated.

The radiation weighting factor for neutrons of various energy has been revised over time and certain agencies have different weighting factors, however despite the variation amongst the agencies, from the graph, for a given energy, A fusion neutron (14.1 MeV) although more energetic, is less biologically harmful as rated in Sieverts, than a fission generated thermal neutron or a fusion neutron slowed to that energy, c. 0.8 MeV.

 

However, some tank armor material contains depleted uranium (DU), common in the US's M1A1 Abrams tank, which incorporates steel-encased depleted uranium armor, a substance that will fast fission when it captures a fast, fusion-generated neutron, and thus on fissioning will produce fission neutrons and fission 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, 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 ceramic second generation heavy metal Chobham armor of the Abrams tank—is an effective radiation shield, to both fission neutrons and gamma rays due to it being a graded Z material. Uranium, being about twice as dense as lead, is thus nearly twice as effective at shielding gamma ray radiation per unit thickness.

Use against ballistic missiles

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 and missile 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". 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 US Atomic Energy Commission mentioning weapons with a "clean, enhanced neutron output" for use as "antimissile defensive warheads." 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 US Polaris 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 a major area of research in the US and UK during the 1960s.

Some sources claim that the neutron flux attack was also the main design goal of the various nuclear-tipped anti-aircraft weapons like the AIM-26 Falcon and CIM-10 Bomarc. One F-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.

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 5,000 rads in silicon chips delivered over seconds to minutes will degrade the function of semiconductors for long periods. 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.

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. 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 unrecoverable glitch by the transient radiation effects on electronics (TREE) effects.

At very high altitudes, at the edge of the atmosphere and above it, another effect comes into play. At lower altitudes, the x-rays generated by the bomb are absorbed by the air and have mean 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. In exoatmospheric 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 "blow off") of the surface creates shock waves that can break up the warhead.

Use as an area denial weapon

In November 2012, during the planning stages of Operation Hammer of God, British Labour peer Lord 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. He proposed to warn the inhabitants to evacuate, then irradiate the area, making it unusable and impassable. Used in this manner, the neutron bomb(s), regardless of burst height, would release neutron activated casing materials used in the bomb, and depending on burst height, create radioactive soil activation products. 

In much the same fashion as the area denial effect resulting from fission product (the substances that make up most fallout) contamination in an area following a conventional surface burst nuclear explosion, as considered in the Korean War by Douglas MacArthur, it would thus be a form of radiological warfare—with the difference that neutron bombs produce half, or less, of the quantity of fission products relative to the same-yield pure fission bomb. Radiological warfare with neutron bombs that rely on fission primaries would thus still produce fission fallout, albeit a comparatively cleaner 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 global fallout.

The easiest to achieve fusion reaction, of deuterium ("D) with tritium (T") creating helium-4, freeing a neutron, and releasing only 3.5 MeV in the form of kinetic energy as the charged alpha particle that will inherently generate heat(which manifests as blast and thermal effects), while the majority of the energy of the reaction(14.1 MeV) is carried away by the uncharged fast neutron. Devices with a higher proportion of yield derived from this reaction would be more efficient in the stand-off asteroid impact avoidance role, due to the penetrative depth of fast-neutrons and the resulting higher momentum transfer that is produced in this "scabbing" of a much larger mass of material free from the main body, as opposed to the shallower surface penetration and ablation of regolith, that is produced by thermal/soft X-rays.

 

However the most effective 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 a salted bomb; a case of zinc-64, produced as a byproduct of depleted zinc oxide enrichment, would for example probably be the most attractive for military use, as when activated, the zinc-65 so formed is a gamma emitter, with a half life of 244 days.

Hypothetical effects of a pure fusion bomb

With considerable overlap between the two devices, the prompt radiation effects of a pure 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 more diminutive atmospheric blast wave than a pure-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 the alpha particle of the D-T reaction, the primary species, that is most responsible for the coulomb explosion/fireball.

Cobalt bomb

From Wikipedia, the free encyclopedia

A cobalt bomb is a type of "salted bomb": a nuclear weapon designed to produce enhanced amounts of radioactive fallout, intended to contaminate a large area with radioactive material. The concept of a cobalt bomb was originally described in a radio program by physicist Leó Szilárd on February 26, 1950. His intent was not to propose that such a weapon be built, but to show that nuclear weapon technology would soon reach the point where it could end human life on Earth, a doomsday device. Such "salted" weapons were requested by the U.S. Air Force and seriously investigated, but not deployed. In the 1964 edition of the U.S. Department of Defense book The Effects of Nuclear Weapons, a new section titled radiological warfare clarified the "Doomsday device" issue.

The Russian Federation has allegedly developed cobalt warheads for use with their Status-6 Oceanic Multipurpose System nuclear torpedoes. However many commentators doubt that this is a real project, and see it as more likely to be a staged leak to intimidate the United States. Amongst other comments on it, Edward Moore Geist wrote a paper in which he says that "Russian decision makers would have little confidence that these areas would be in the intended locations" and Russian military experts are cited as saying that "robotic torpedoes could have other purposes, such as delivering deep-sea equipment or installing surveillance devices."

The Operation Antler/Round 1 test by the British at the Tadje site in the Maralinga range in Australia on September 14, 1957, tested a bomb using cobalt pellets as a radiochemical tracer for estimating yield. This was considered a failure and the experiment was not repeated. In Russia, the triple "taiga" nuclear salvo test, as part of the preliminary March 1971 Pechora–Kama Canal project, produced relatively high amounts of Co-60 from the steel that surrounded the Taiga devices, with this fusion generated neutron activation product being responsible for about half of the gamma dose now (2011) at the test site. This high percentage contribution is largely because the devices did not rely much at all on fission reactions and thus the quantity of gamma emitting caesium-137 fallout, is therefore comparatively low. Photosynthesizing vegetation exists all around the lake that was formed.

Mechanism

A cobalt bomb could be made by placing a quantity of ordinary cobalt metal (⁵⁹Co) around a thermonuclear bomb. When the bomb explodes, the neutrons produced by the fusion reaction in the secondary stage of the thermonuclear bomb's explosion would transmute the cobalt to the radioactive cobalt-60 (⁶⁰Co), which would be vaporized by the explosion. The cobalt would then condense and fall back to Earth with the dust and debris from the explosion, contaminating the ground. 

The deposited cobalt-60 would have a half-life of 5.27 years, decaying into ⁶⁰Ni and emitting two gamma rays with energies of 1.17 and 1.33 MeV, hence the overall nuclear equation of the reaction is: 

⁵⁹
₂₇Co
+ n → ⁶⁰
₂₇Co
→ ⁶⁰
₂₈Ni
+ e⁻ + gamma rays.

Nickel-60 is a stable isotope and undergoes no further decays after emitting the gamma rays. 

The 5.27 year half life of the ⁶⁰Co is long enough to allow it to settle out before significant decay has occurred, and to render it impractical to wait in shelters for it to decay, yet short enough that intense radiation is produced. Many isotopes are more radioactive (gold-198, tantalum-182, zinc-65, sodium-24, and many more), but they would decay faster, possibly allowing some population to survive in shelters.

Fallout from cobalt bombs vs. other nuclear weapons

Fission products are more deadly than neutron-activated cobalt in the first few weeks following detonation. After one to six months, the fission products from even a large-yield thermonuclear weapon decay to levels tolerable by humans. The large-yield three-stage (fission–fusion–fission) thermonuclear weapon is thus automatically a weapon of radiological warfare, but its fallout decays much more rapidly than that of a cobalt bomb. A cobalt bomb's fallout on the other hand would render affected areas effectively stuck in this interim state for decades: habitable, but not safe for constant habitation.

Initially, gamma radiation from the fission products of an equivalent size fission-fusion-fission bomb are much more intense than Co-60: 15,000 times more intense at 1 hour; 35 times more intense at 1 week; 5 times more intense at 1 month; and about equal at 6 months. Thereafter fission product fallout radiation levels drop off rapidly, so that Co-60 fallout is 8 times more intense than fission at 1 year and 150 times more intense at 5 years. The very long-lived isotopes produced by fission would overtake the ⁶⁰Co again after about 75 years.

Theoretically, a device containing 510 metric tons of Co-59 can spread 1 g of the material to each square km of the Earth's surface (510,000,000 km²). If one assumes that all of the material is converted to Co-60 at 100 percent efficiency and if it is spread evenly across the Earth's surface, it is possible for a single bomb to kill every person on Earth. However, in fact, complete 100% conversion into Co-60 is unlikely; a 1957 British experiment at Maralinga showed that Co-59's neutron absorption ability was much lower than predicted, resulting in a very limited formation of Co-60 isotope in practice. 

In addition, another important point in considering the effects of cobalt bombs is that deposition of fallout is not even throughout the path downwind from a detonation, so that there are going to be areas relatively unaffected by fallout and places where there is unusually intense fallout, so that the Earth would not be universally rendered lifeless by a cobalt bomb. The fallout and devastation following a nuclear detonation does not scale upwards linearly with the explosive yield (equivalent to tons of TNT). As a result, the concept of "overkill"—the idea that one can simply estimate the destruction and fallout created by a thermonuclear weapon of the size postulated by Leo Szilard's "cobalt bomb" thought experiment by extrapolating from the effects of thermonuclear weapons of smaller yields—is fallacious.

Example of radiation levels vs. time

Assume a cobalt bomb deposits intense fallout causing a dose rate of 10 sieverts (Sv) per hour. At this dose rate, any unsheltered person exposed to the fallout would receive a lethal dose in about 30 minutes (assuming a median lethal dose of 5 Sv). People in well-built shelters would be safe due to radiation shielding. 

After one half-life of 5.27 years, only half of the cobalt-60 will have decayed, and the dose rate in the affected area would be 5 Sv/hour. At this dose rate, a person exposed to the radiation would receive a lethal dose in 1 hour. 

After 10 half-lives (about 53 years), the dose rate would have decayed to around 10 mSv/hour. At this point, a healthy person could spend 1 to 4 days exposed to the fallout with no immediate effects. 

After 20 half-lives (about 105 years), the dose rate would have decayed to around 10 μSv/hour. At this stage, humans could remain unsheltered full-time since their yearly radiation dose would be about 80 mSv. However, this yearly dose rate is on the order of 30 times greater than the peacetime exposure rate of 2.5 mSv/year. As a result, the rate of cancer incidence in the survivor population would likely increase. 

After 25 half-lives (about 130 years), the dose rate from cobalt-60 would have decayed to less than 0.4 μSv/hour (natural background radiation) and could be considered negligible.

Decontamination

In practice it is unlikely that people would simply sit and wait for nuclear decay to go to completion, as in all historical fallout cases, decontamination of valuable land has occurred. This is most commonly done with the use of simple equipment such as lead glass covered excavators and bulldozers, similar to those employed in the Lake Chagan project. By skimming off the thin layer of fallout on the topsoil surface and burying it in the likes of a deep trench along with isolating it from ground water sources, the gamma air dose is cut by orders of magnitude. The decontamination after the Goiânia accident in Brazil 1987 and the possibility of a "dirty bomb" with Co-60, which has similarities with the environment that one would be faced with after a nuclear yielding cobalt bomb's fallout had settled, has prompted the invention of "Sequestration Coatings" and cheap liquid phase sorbents for Co-60 that would further aid in decontamination, including that of water.

Russian "Status-6"

In 2015, a page from an apparent Russian nuclear-armed torpedo design was accidentally or deliberately leaked. The design was titled "Oceanic Multipurpose System Status-6". The document stated the torpedo would create "wide areas of radioactive contamination, rendering them unusable for military, economic or other activity for a long time". Its payload would be "many tens of megatons in yield". Russian government newspaper Rossiiskaya Gazeta speculated that the warhead would be a cobalt bomb. It is not known whether the Status-6 is a real project, or whether it is Russian disinformation. In 2018 the Pentagon's annual Nuclear Posture Review stated Russia is developing a system called the "Status-6 Oceanic Multipurpose System". If Status-6 does exist, it is not publicly known whether the leaked 2015 design is accurate, nor whether the 2015 claim that the torpedo might be a cobalt bomb is genuine. Status-6 was officially disclosed and confirmed by Vladimir Putin in 2018 during his display of new Russian offensive weapons, including the Satan-2, Air Launched Iskander, Nuclear cruise-missile, and hypersonic glider.

In popular culture

In the 4th act of the classic Star Trek episode "Obsession", Ensign Garrovick refers to 10,000 cobalt bombs not equaling the power of less than one ounce of antimatter. 

In Beneath the Planet of the Apes (1970) the main character, upon seeing that the underground people worship a giant bomb that can wipe out the world, comments "They finally built one with a cobalt casing" in reference to a cobalt bomb that could wipe out the world. Similarly, in the bestselling On the Beach (1957) the cobalt bomb was a symbol of man's hubris.

In the black comedy Dr. Strangelove, or: How I Learned to Stop Worrying and Love the Bomb (1964), a type of cobalt-salted bomb is employed, with a Dead Hand mechanism, by the Soviet Union as a nuclear deterrent: if the system detects any nuclear attack, the doomsday device will be automatically unleashed. With unfortunate timing, a mentally ill American officer orders an attack on the USSR. One American bomber piloted by a hapless and unknowing crew gets through to their target; the Dead Hand mechanism works as designed and initiates a worldwide nuclear holocaust. The Russian Ambassador says "If you take, say, fifty H-bombs in the hundred megaton range and jacket them with cobalt thorium G, when they are exploded they will produce a doomsday shroud. A lethal cloud of radioactivity which will encircle the earth for ninety-three years!"

In the Spectreman episodes "Smash Alien Igorl!!" and "Enigma of the Cobalt Monster", the villainous Dr. Gori and race of Igorl aliens create a cobalt bomb from a heavy amount of cobalt found beneath a small village and place it within a monster, planning for it to destroy the world due to it reacting strongly to Earth's polluted atmosphere.

In the 2019 video game Metro Exodus the player visits the Russian city of Novosibirsk which was hit with at least one cobalt warhead during a worldwide nuclear war in the year 2014, resulting in catastrophic levels of radiation, and easily the most irradiated area visited in the three Metro games. While the city is left largely standing even twenty years after the cobalt warhead's detonation, the radiation in the city is so lethal that even with lead-lined full enclosure suits, the player can only spend a few minutes on the surface before receiving lethal amounts of radiation poisoning. During their visit, the player discovers that the survivors of the attack survived underground for nineteen years, but only due to constant injections of anti-radiation medicine.

Dirty bomb

From Wikipedia, the free encyclopedia

A dirty bomb or radiological dispersal device (RDD) is a speculative radiological weapon that combines radioactive material with conventional explosives. The purpose of the weapon is to contaminate the area around the dispersal agent/conventional explosion with radioactive material, serving primarily as an area denial device against civilians. It is, however, not to be confused with a nuclear explosion, such as a fission bomb, which by releasing nuclear energy produces blast effects far in excess of what is achievable by the use of conventional explosives. 

Though an RDD would be designed to disperse radioactive material over a large area, a bomb that uses conventional explosives and produces a blast wave would be far more lethal to people than the hazard posed by radioactive material that may be mixed with the explosive. At levels created from probable sources, not enough radiation would be present to cause severe illness or death. A test explosion and subsequent calculations done by the United States Department of Energy found that assuming nothing is done to clean up the affected area and everyone stays in the affected area for one year, the radiation exposure would be "fairly high" but not fatal. Recent analysis of the nuclear fallout from the Chernobyl disaster confirms this, showing that the effect on many people in the surrounding area, although not those in proximity, was almost negligible.

Since a dirty bomb is unlikely to cause many deaths by radiation exposure, many do not consider this to be a weapon of mass destruction. Its purpose would presumably be to create psychological, not physical, harm through ignorance, mass panic, and terror. For this reason dirty bombs are sometimes called "weapons of mass disruption". Additionally, containment and decontamination of thousands of victims, as well as decontamination of the affected area might require considerable time and expense, rendering areas partly unusable and causing economic damage.

Dirty bombs and terrorism

Since the 9/11 attacks the fear of terrorist groups using dirty bombs has increased immensely, which has been frequently reported in the media. The meaning of terrorism used here, is described by the U.S. Department of Defense's definition, which is "the calculated use of unlawful violence or threat of unlawful violence to inculcate fear; intended to coerce or to intimidate governments or societies in the pursuit of goals that are generally political, religious, or ideological objectives". There have only ever been two cases of caesium-containing bombs, and neither was detonated. Both involved Chechnya. The first attempt of radiological terror was carried out in November 1995 by a group of Chechen separatists, who buried a caesium-137 source wrapped in explosives at the Izmaylovsky Park in Moscow. A Chechen rebel leader alerted the media, the bomb was never activated, and the incident amounted to a mere publicity stunt.

In December 1998, a second attempt was announced by the Chechen Security Service, who discovered a container filled with radioactive materials attached to an explosive mine. The bomb was hidden near a railway line in the suburban area Argun, ten miles east of the Chechen capital of Grozny. The same Chechen separatist group was suspected to be involved. Despite the increased fear of a dirty bombing attack, it is hard to assess whether the actual risk of such an event has increased significantly. The following discussions on implications, effects and probability of an attack, as well as indications of terror groups planning such, are based mainly on statistics, qualified guessing and a few comparable scenarios.

Effect of a dirty bomb explosion

When dealing with the implications of a dirty bomb attack, there are two main areas to be addressed: (i) the civilian impact, not only dealing with immediate casualties and long term health issues, but also the psychological effect and then (ii) the economic impact. With no prior event of a dirty bomb detonation, it is considered difficult to predict the impact. Several analyses have predicted that RDDs will neither sicken nor kill many people.

Accidents with radioactives

The effects of uncontrolled radioactive contamination have been reported several times.

One example is the radiological accident occurring in Goiânia, Brazil, between September 1987 and March 1988: Two metal scavengers broke into an abandoned radiotherapy clinic and removed a teletherapy source capsule containing powdered caesium-137 with an activity of 50 TBq. They brought it back to the home of one of the men to take it apart and sell as scrap metal. Later that day both men were showing acute signs of radiation illness with vomiting and one of the men had a swollen hand and diarrhea. A few days later one of the men punctured the 1 mm thick window of the capsule, allowing the caesium chloride powder to leak out and when realizing the powder glowed blue in the dark, brought it back home to his family and friends to show it off. After 2 weeks of spread by contact contamination causing an increasing number of adverse health effects, the correct diagnosis of acute radiation sickness was made at a hospital and proper precautions could be put into procedure. By this time 249 people were contaminated, 151 exhibited both external and internal contamination of which 20 people were seriously ill and 5 people died.

The Goiânia incident to some extent predicts the contamination pattern if it is not immediately realized that the explosion spread radioactive material, but also how fatal even very small amounts of ingested radioactive powder can be. This raises worries of terrorists using powdered alpha emitting material, that if ingested can pose a serious health risk, as in the case of deceased former K.G.B. spy Alexander Litvinenko, who either ate, drank or inhaled polonium-210. "Smoky bombs" based on alpha emitters might easily be just as dangerous as beta or gamma emitting dirty bombs.

Public perception of risks

For the majority involved in an RDD incident, the radiation health risks (i.e. increased probability of developing cancer later in life due to radiation exposure) are comparatively small, comparable to the health risk from smoking five packages of cigarettes on a daily basis. The fear of radiation is not always logical. Although the exposure might be minimal, many people find radiation exposure especially frightening because it is something they cannot see or feel, and it therefore becomes an unknown source of danger. Dealing with public fear may prove the greatest challenge in case of an RDD event. Policy, science and media may inform the public about the real danger and thus reduce the possible psychological and economic effects.

Statements from the U.S. government after 9/11 may have contributed unnecessarily to the public fear of a dirty bomb. When United States Attorney General John Ashcroft on June 10, 2002, announced the arrest of José Padilla, allegedly plotting to detonate such a weapon, he said:

[A] radioactive "dirty bomb" (...) spreads radioactive material that is highly toxic to humans and can cause mass death and injury.

— Attorney General John Ashcroft

This public fear of radiation also plays a big role in why the costs of an RDD impact on a major metropolitan area (such as lower Manhattan) might be equal to or even larger than that of the 9/11 attacks. Assuming the radiation levels are not too high and the area does not need to be abandoned such as the town of Pripyat near the Chernobyl reactor, an expensive and time consuming cleanup procedure will begin. This will mainly consist of tearing down highly contaminated buildings, digging up contaminated soil and quickly applying sticky substances to remaining surfaces so that radioactive particles adhere before radioactivity penetrates the building materials. These procedures are the current state of the art for radioactive contamination cleanup, but some experts say that a complete cleanup of external surfaces in an urban area to current decontamination limits may not be technically feasible. Loss of working hours will be vast during cleanup, but even after the radiation levels reduce to an acceptable level, there might be residual public fear of the site including possible unwillingness to conduct business as usual in the area. Tourist traffic is likely never to resume.

There is also a psychological warfare element to radioactive substances. Visceral fear is not widely aroused by the daily emissions from coal burning, for example, even though a National Academy of Sciences study found this causes 10,000 premature deaths a year in the US population of 317,413,000. Medical errors leading to death in U.S. hospitals are estimated to be between 44,000 and 98,000. It is "only nuclear radiation that bears a huge psychological burden — for it carries a unique historical legacy".

Constructing and obtaining material for a dirty bomb

In order for a terrorist organization to construct and detonate a dirty bomb, it must acquire radioactive material. Possible RDD material could come from the millions of radioactive sources used worldwide in the industry, for medical purposes and in academic applications mainly for research. Of these sources, only nine reactor produced isotopes stand out as being suitable for radiological terror: americium-241, californium-252, caesium-137, cobalt-60, iridium-192, plutonium-238, polonium-210, radium-226 and strontium-90, and even from these it is possible that radium-226 and polonium-210 do not pose a significant threat. Of these sources the U.S. Nuclear Regulatory Commission has estimated that within the U.S., approximately one source is lost, abandoned or stolen every day of the year. Within the European Union the annual estimate is 70. There exist thousands of such "orphan" sources scattered throughout the world, but of those reported lost, no more than an estimated 20 percent can be classified as a potential high security concern if used in a RDD. Especially Russia is believed to house thousands of orphan sources, which were lost following the collapse of the Soviet Union. A large but unknown number of these sources probably belong to the high security risk category. Noteworthy are the beta emitting strontium-90 sources used as radioisotope thermoelectric generators for beacons in lighthouses in remote areas of Russia. In December 2001, three Georgian woodcutters stumbled over such a power generator and dragged it back to their camp site to use it as a heat source. Within hours they suffered from acute radiation sickness and sought hospital treatment. The International Atomic Energy Agency (IAEA) later stated that it contained approximately 40 kilocuries (1.5 PBq) of strontium, equivalent to the amount of radioactivity released immediately after the Chernobyl accident (though the total radioactivity release from Chernobyl was 2500 times greater at around 100 MCi (3,700 PBq)).

Although a terrorist organization might obtain radioactive material through the "black market", and there has been a steady increase in illicit trafficking of radioactive sources from 1996 to 2004, these recorded trafficking incidents mainly refer to rediscovered orphan sources without any sign of criminal activity, and it has been argued that there is no conclusive evidence for such a market. In addition to the hurdles of obtaining usable radioactive material, there are several conflicting requirements regarding the properties of the material the terrorists need to take into consideration: First, the source should be "sufficiently" radioactive to create direct radiological damage at the explosion or at least to perform societal damage or disruption. Second, the source should be transportable with enough shielding to protect the carrier, but not so much that it will be too heavy to maneuver. Third, the source should be sufficiently dispersible to effectively contaminate the area around the explosion.

An example of a worst-case scenario is a terror organization possessing a source of very highly radioactive material, e.g. a strontium-90 thermal generator, with the ability to create an incident comparable to the Chernobyl accident. Although the detonation of a dirty bomb using such a source might seem terrifying, it would be hard to assemble the bomb and transport it without severe radiation damage and possible death of the perpetrators involved. Shielding the source effectively would make it almost impossible to transport and a lot less effective if detonated. 

Due to the three constraints of making a dirty bomb, RDDs might still be defined as "high-tech" weapons and this is probably why they have not been used up to now.

Possibility of terrorist groups using dirty bombs

The present assessment of the possibility of terrorists using a dirty bomb is based on cases involving ISIS. This is because the attempts by this group to acquire a dirty bomb coming to light in all forms of media, in part due to the attention this group received for their involvement in the London bridge attack. 

On 8 May 2002, José Padilla (a.k.a. Abdulla al-Muhajir) was arrested on suspicion that he was an Al-Qaeda terrorist planning to detonate a dirty bomb in the U.S. This suspicion was raised by information obtained from an arrested top Al-Qaeda official in U.S. custody, Abu Zubaydah, who under interrogation revealed that the organization was close to constructing a dirty bomb. Although Padilla had not obtained radioactive material or explosives at the time of arrest, law enforcement authorities uncovered evidence that he was on reconnaissance for usable radioactive material and possible locations for detonation. It has been doubted whether José Padilla was preparing such an attack, and it has been claimed that the arrest was highly politically motivated, given the pre-9/11 security lapses by the CIA and FBI.

Later, these charges against José Padilla were dropped. Although there was no hard evidence for Al-Qaeda possessing a dirty bomb, there is a broad agreement that Al-Qaeda poses a potential dirty bomb attack threat because they need to overcome the alleged image that the U.S. and its allies are winning the war against terror. A further concern is the argument, that "if suicide bombers are prepared to die flying airplanes into building, it is also conceivable that they are prepared to forfeit their lives building dirty bombs". If this would be the case, both the cost and complexity of any protective systems needed to allow the perpetrator to survive long enough to both build the bomb and carry out the attack, would be significantly reduced.

Several other captives were alleged to have played a role in this plot. Guantanamo captive Binyam Mohammed has alleged he was subjected to extraordinary rendition, and that his confession of a role in the plot was coerced through torture. He sought access through the American and United Kingdom legal systems to provide evidence he was tortured. Guantanamo military commission prosecutors continue to maintain the plot was real, and charged Binyam for his alleged role in 2008. However they dropped this charge in October 2008, but maintain they could prove the charge and were only dropping the charge to expedite proceedings. US District Court Judge Emmet G. Sullivan insisted that the administration still had to hand over the evidence that justified the dirty bomb charge, and admonished United States Department of Justice lawyers that dropping the charge "raises serious questions in this court's mind about whether those allegations were ever true."

In 2006, Dhiren Barot from North London pleaded guilty of conspiring to murder innocent people within the United Kingdom and United States using a radioactive dirty bomb. He planned to target underground car parks within the UK and buildings in the U.S. such as the International Monetary Fund, World Bank buildings in Washington D.C., the New York Stock Exchange, Citigroup buildings and the Prudential Financial buildings in Newark, New Jersey. He also faces 12 other charges including, conspiracy to commit public nuisance, seven charges of making a record of information for terrorist purposes and four charges of possessing a record of information for terrorist purposes. Experts say if the plot to use the dirty bomb was carried out "it would have been unlikely to cause deaths, but was designed to affect about 500 people."

In January 2009, a leaked FBI report described the results of a search of the Maine home of James G. Cummings, a white supremacist who had been shot and killed by his wife. Investigators found four one-gallon containers of 35 percent hydrogen peroxide, uranium, thorium, lithium metal, aluminum powder, beryllium, boron, black iron oxide and magnesium as well as literature on how to build dirty bombs and information about cesium-137, strontium-90 and cobalt-60, radioactive materials. Officials confirmed the veracity of the report but stated that the public was never at risk.

In April 2009, the Security Service of Ukraine announced the arrest of a legislator and two businessmen from the Ternopil Oblast. Seized in the undercover sting operation was 3.7 kilograms of what was claimed by the suspects during the sale as plutonium-239, used mostly in nuclear reactors and nuclear weapons, but was determined by experts to be probably americium, a "widely used" radioactive material which is commonly used in amounts of less than 1 milligram in smoke detectors, but can also be used in a dirty bomb. The suspects reportedly wanted US$ 10 million for the material, which the Security Service determined was produced in Russia during the era of the Soviet Union and smuggled into Ukraine through a neighboring country.

In July 2014, ISIS militants seized 88 pounds (40 kg) of uranium compounds from Mosul University. The material was unenriched and so could not be used to build a conventional fission bomb, but a dirty bomb is a theoretical possibility. However, uranium's relatively low radioactivity makes it a poor candidate for use in a dirty bomb.

Little is known about civil preparedness to respond to a dirty bomb attack. The Boston Marathon appeared to many to be a situation with high potential for use of a dirty bomb as a terrorist weapon. However, the bombing attack that occurred on April 15, 2013 did not involve use of dirty bombs. Any radiological testing or inspections that may have occurred following the attack were either conducted sub rosa or not at all. Also, there was no official dirty bomb "all clear" issued by the Obama administration. Massachusetts General Hospital had, apparently under their own disaster plan, issued instructions to their emergency room to be prepared for incoming radiation poisoning cases.

Terrorist organizations may also capitalize on the fear of radiation to create weapons of mass disruption rather than weapons of mass destruction. A fearful public response may in itself accomplish the goals of a terrorist organization to gain publicity or destabilize society. Even simply stealing radioactive materials may trigger a panic reaction from the general public. Similarly, a small-scale release of radioactive materials or a threat of such a release may be considered sufficient for a terror attack. Particular concern is directed towards the medical sector and healthcare sites which are "intrinsically more vulnerable than conventional licensed nuclear sites". Opportunistic attacks may range to even kidnapping patients whose treatment involve radioactive materials. Of note is the public reaction to the Goiânia accident, in which over 100,000 people admitted themselves to monitoring, while only 49 were admitted to hospitals. Other benefits to a terrorist organization of a dirty bomb include economic disruption in the area affected, abandonment of affected assets (such a buildings, subways) due to public concern, and international publicity useful for recruitment.

Dirty bomb tests

Israel carried out a four-year series of tests on nuclear explosives to measure the effects were “hostile forces” ever to use them against Israel, Israel’s Haaretz daily newspaper reported June 8, 2015.

Detection and prevention

Dirty bombs may be prevented by detecting illicit radioactive materials in shipping with tools such as a Radiation Portal Monitor. Similarly, unshielded radioactive materials may be detected at checkpoints by Geiger Counters, gamma-ray detectors, and even Customs and Border Patrol (CBS) pager-sized radiation detectors. Hidden materials may also be detected by x-ray inspection and heat emitted may be picked up by infrared detectors. Such devices, however, may be circumvented by simply transporting materials across unguarded stretches of coastline or other barren border areas.

One proposed method for detecting shielded Dirty Bombs is Nanosecond Neutron Analysis (NNA). Designed originally for the detection of explosives and hazardous chemicals, NNA is also applicable to fissile materials. NNA determines what chemicals are present in an investigated device by analyzing emitted γ-emission neutrons and α-particles created from a reaction in the neutron generator. The system records the temporal and spatial displacement of the neutrons and α-particles within separate 3D regions. A prototype dirty-bomb detection device created with NNA is demonstrated to be able to detect uranium from behind a 5 cm-thick lead wall. Other radioactive material detectors include Radiation Assessment and Identification (RAID) and Sensor for Measurement and Analysis of Radiation Transients, both developed by Sandia National Laboratories.

The International Atomic Energy Agency (IAEA) recommends certain devices be used in tandem at country borders to prevent transfer of radioactive materials, and thus the building of dirty bombs. They define the four main goals of radiation detection instruments as detection, verification, assessment and localization, and identification as a means to escalate a potential radiological situation. The IAEA also defines the following types of instruments:

• Pocket-Type Instruments: these instruments provide a low-power, mobile option to detection that allows for security officers to passively scan an area for radioactive materials. These devices should be easily worn, should have an alarm threshold of three times normal radiation levels, and should have a long battery life - over 800 hours.
• Handheld Instruments: these instruments may be used to detect all types of radiation (including neutron) and may be used to search specific targets flexibly. These instruments should aim for ease of use and speed, ideally weighing less than 2 kg and being able to make measurements in less than a second.
• Fixed, installed instruments: these instruments provide a continuous, automatic detection system that can monitor pedestrians and vehicles that pass through. To work effectively pedestrians and vehicles should be led close to the detectors, as performance is directly related to range.

Legislative and regulatory actions can also be used to prevent access to materials needed to create a dirty bomb. Examples include the 2006 U.S. Dirty Bomb Bill, the Yucca Flats proposal, and the Nunn-Lungar act. Similarly, close monitoring and restrictions of radioactive materials may provide security for materials in vulnerable private-sector applications, most notably in the medical sector where such materials are used for treatments. Suggestions for increased security include isolation of materials in remote locations and strict limitation of access.

One way to mitigate a major effect of a radiological weapons may also be to educate the public on the nature of radioactive materials. As one of the major concerns of a dirty bomb is the public panic proper education may prove a viable counter-measure. Education on radiation is considered by some to be "the most neglected issue related to radiological terrorism".

Personal safety

The Dirty Bomb Fact Sheet from FEMA states that the main danger of a dirty bomb comes from the initial blast rather than the radioactive materials. To mitigate the risk of radiation exposure, however, FEMA suggests the following guidelines:

• Covering the mouth/nose with cloth to reduce risk of breathing in radioactive materials.
• Avoiding touching materials touched by the explosion.
• Quickly relocating inside to shield from radiation.
• Remove and pack up clothes. Keep clothes until instructed by authorities how to dispose of them.
• Keep radioactive dust outside.
• Remove all dust possible by showering with soap and water.
• Avoid taking potassium iodide, as it only prevents effects from radioactive iodine and may instead cause a dangerous reaction.

Other uses of the term

The term has also been used historically to refer to certain types of nuclear weapons. Due to the inefficiency of early nuclear weapons, only a small amount of the nuclear material would be consumed during the explosion. Little Boy had an efficiency of only 1.4%. Fat Man, which used a different design and a different fissile material, had an efficiency of 14%. Thus, they tended to disperse large amounts of unused fissile material, and the fission products, which are on average much more dangerous, in the form of nuclear fallout. During the 1950s, there was considerable debate over whether "clean" bombs could be produced and these were often contrasted with "dirty" bombs. "Clean" bombs were often a stated goal and scientists and administrators said that high-efficiency nuclear weapon design could create explosions which generated almost all of their energy in the form of nuclear fusion, which does not create harmful fission products. 

But the Castle Bravo accident of 1954, in which a thermonuclear weapon produced a large amount of fallout which was dispersed among human populations, suggested that this was not what was actually being used in modern thermonuclear weapons, which derive around half of their yield from a final fission stage of the fast fissioning of the uranium tamper of the secondary. While some proposed producing "clean" weapons, other theorists noted that one could make a nuclear weapon intentionally "dirty" by "salting" it with a material, which would generate large amounts of long-lasting fallout when irradiated by the weapon core. These are known as salted bombs; a specific subtype often noted is a cobalt bomb.

In popular culture

• In the 1964 British movie Goldfinger, both Auric Goldfinger and James Bond refer to the nuclear device being smuggled into Fort Knox as "dirty."
• The crime drama television series Numb3rs has an episode that revolves around a dirty bomb (season 1, episode 10).
• In a two-part 2011 episode of Castle, former US soldiers plot to detonate a dirty bomb in New York City and frame a Syrian immigrant for the crime.
• In the 2012 series finale of Flashpoint, an officer is poisoned by caesium from a dirty bomb and is administered Prussian blue to assist in recovery.
• In the 2013 Indian movie Vishwaroopam, the plot revolves around a dirty bomb developed by scraping caesium from oncological equipment to trigger a blast in New York City.
• In the 2014 movie, Batman: Assault on Arkham, the Joker has a dirty bomb which he plans on detonating in Gotham.
• In the January 14, 2016 Republican presidential debates, Ben Carson referenced dirty bombs twice when speaking on US foreign policy.
• In the June 1, 2015 game by Splash Damage, Dirty Bomb, the game is played in a dirty bomb fallout area in London.
• In the Madam Secretary episode "Right of the Boom", a dirty bomb is detonated at a women's education conference in Washington, D.C.
• The American political drama web television series House of Cards has an episode that revolves around a dirty bomb (season 5, episode 7).
• In the 2006 movie Right At Your Door multiple dirty bombs are detonated in Los Angeles.
• In the 2018 video game Detroit: Become Human one of the endings has a character setting off a dirty bomb in southern Detroit.
• In the 2019 video game Metro Exodus one of Russia's major cities, Novosibirsk, has been struck by a dirty bomb during the end of World War III.