A dirty bomb or radiological dispersal device is a 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 not to be confused with a nuclear explosion, such as a fission bomb, which produces blast effects far in excess of what is achievable by the use of conventional explosives. Unlike the rain of radioactive material from a typical fission bomb, a dirty bomb's radiation can be dispersed only within a few hundred meters or a few miles of the explosion.
Dirty bombs have never been used, only tested. They are designed to disperse radioactive material over a certain area. They act through the effects of radioactive contamination on the environment and related health effects of radiation poisoning in the affected populations. The containment and decontamination of victims, as well as decontamination of the affected area require considerable time and expenses, rendering areas partly unusable and causing economic damage. Dirty bombs might be used to create mass panic as a weapon of terror.
Effect of a dirty bomb explosion When dealing with the implications of a dirty bomb attack, there are two main areas to be addressed: the civilian impact, not only dealing with immediate casualties and long term health issues, but also the psychological effect; and 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 radiological dispersal devices will neither sicken nor kill many people.Reshetin (2005); Dingle (2005)
Differences between dirty bombs and fission bombs Dirty bomb Explosives combined with radioactive materials Detonation vaporizes or aerosolizes radioactive material and propels it into the air Not a nuclear detonationFission bomb Caused by an uncontrolled nuclear chain reaction with highly enriched uranium or weapons-grade plutonium Sphere of fissile material (pit) surrounded by explosive lenses Initial explosion produces imploding shock wave that compresses pit inward, creating supercritical mass by increasing the density of fissile material. Neutrons from either modulated neutron initiator or external neutron generator start chain reaction in compressed pit Resulting fission chain reaction causes bomb to explode with tremendous force: nuclear detonation Source: Adapted from Levi MA, Kelly HC. "Weapons of mass disruption". Sci Am. 2002 Nov;287(5):76-81.
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 them had a swollen hand and diarrhea. A few days later one of the men punctured the 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 two 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 whom 20 people were seriously ill and five people died.King (2004); Zimmerman and Loeb (2004); Sohier and Hardeman (2006)
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.Zimmerman and Loeb (2004) This raises worries of terrorists using powdered alpha emitting material, that if ingested can pose a serious health risk,Mullen et al. (2002); Reshetin (2005) as in the case of Alexander Litvinenko, who was poisoned by tea with polonium-210. "Smoky bombs" based on alpha emitters might be just as dangerous as beta or gamma emitting dirty bombs.Zimmerman (2006)
Public perception of risks 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.Johnson (2003) 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 a radiological dispersal device 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,"The Lifeless Silence of Pripyat", Time, June 23, 1986. 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.Vantine and Crites (2002); Zimmerman and Loeb (2004); Weiss (2005) 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.
Dirty bombs and terrorism
Since the 9/11 attacks, the fear of terrorist groups using dirty bombs has increased, which has been frequently reported in the media.Petroff (2007) 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."
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 radiological dispersal device material could come from the millions of radioactive sources used worldwide in the industry, for medical purposes and in academic applications mainly for research.Ferguson et al. (2003); Frost (2005) 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,Frost (2005) and even from these it is possible that radium-226 and polonium-210 do not pose a significant threat.Ferguson et al. (2003) 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.Ferguson et al. (2003); Zimmerman and Loeb (2004) 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 potential high security concerns if used in a radiological dispersal device. 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. These include the beta-emitting strontium-90 sources used as radioisotope thermoelectric generators for beacons in lighthouses in remote areas of Russia.Burgess (2003); Van Tuyle and Mullen (2003); Sohier and Hardeman (2006) 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 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 ).
Although a terrorist organization might obtain radioactive material through the "black market",King (2004); Hoffman (2006) 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.Belyaninov (1994); Frost (2005) 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.Sohier and Hardeman (2006)
Possibility of use by terrorist groups The first attempt of radiological terror was reportedly 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.King (2004) 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.Edwards (2004)
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 terrorist 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.Ferguson et al. (2003); Hosenball et al. (2002) 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.Burgess (2003); King (2004)