Because a terrorist dirty bomb is unlikely to cause many deaths, 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 panic-stricken victims, as well as decontamination of the affected area might require considerable time and expense, rendering affected areas partly unusable and causing economic damage.
It is thought that during the 1960s the UK Ministry of Defence evaluated RDDs, deciding that a far better effect was achievable by simply using more high explosive in place of the radioactive material.
Up until now, no dirty bomb has ever been found or used.
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. 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.
Since the 9/11 attacks the fear of terrorist groups using dirty bombs has increased significantly, which has been frequently reported in the media . The meaning of the term terrorism used here, can be 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" . Although there exists an increased fear of terrorists deploying dirty bombs, there has only ever been two cases of such, and neither was detonated. Both involved Chechnya. The first ever 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, 10 miles east of the Chechen capital of Grozny. The same Chechen separatist group as above was suspected to be involved in the incident . It should be noted that despite the enhanced fear of a dirty bombing attack, it is very 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, will be based mainly on statistics, qualified guessing and a few comparable scenarios.
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 new worries of terrorists using powdered alpha emitting material, that if ingested can pose a serious health risk , as in the case of now 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 .
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:
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 to adhere the radioactive particles before they penetrate into the building materials . These procedures are the current state of the art for radioactive contamination cleanup, but some experts claim 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 the cleanup period, but even after the procedures have been accomplished and the radiation levels reduced 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.
In order for a terrorist organization to construct and detonate a dirty bomb, they must first acquire radioactive material either by stealing it or buying through legal or illegal channels. 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 every day of the year either because they are lost, abandoned or stolen. Within the European Union the annual estimate is 70 . There exists 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 very strong Russian beta emitting strontium-90 sources used as thermoelectric power generators for beacons in lighthouses in remote areas . 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 an amount of strontium equivalent to the amount of radiation released immediately after the Chernobyl accident.
Although there exists a worry that terrorist organizations might obtain radioactive material through a "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 real 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 manoeuvre. 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.
Because of the three above mentioned constraints in making an effective dirty bomb, RDDs might still be defined as "high-tech" weapons and this is probably why they have not been used up to now.
The present assessment of the possibility of terrorists using a dirty bomb is based on cases involving one terrorist organization, namely Al-Qaeda. This is because the attempts by this group to acquire a dirty bomb are the most well-described in the literature, in part due to the attention this group received for their involvement in the 9/11 attacks. Other groups may also be working on acquiring a dirty bomb, but they are not considered here due to the lack of publicly available information.
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 any 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 the alleged plotter, José Padilla, was preparing such an attack, and 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.
More recently 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."