Dirty Bombs and Other Radiological Weapons

by Wm. Robert Johnston
last updated 15 September 2005


So-called "dirty bombs" are one type of radiological weapon. Radiological weapons disperse radioactive material with conventional explosives, by fire, or otherwise by dilution (as in water or air).

Dirty bombs have been the topic of much public discussion since the Al Qaeda attacks of September 11, 2001. The quality of this discussion has varied considerably. Consider some common misconceptions contrasted with facts:

  • Myth: Dirty bombs would cause large numbers of casualities.
    Fact: In general, radiological weapons would not be effective at producing casualties, although the economic and psychological impact could be severe.
  • Myth: The longer the half-life of a radioactive material, the deadlier it is.
    Fact: Radioactive material is not necessarily more dangerous if it has a longer half-life. For a given number of radioactive atoms, a longer half-life means the quantity is less radioactive.
  • Myth: A devastating dirty bomb could be made with low-level nuclear waste or weapons-grade materials.
    Fact: Nuclear wastes are less likely options for weapon source material. Commercial radioactive sources are a security concern because of the combination of their activity levels and accessibility.
  • Myth: Terrorists need only attack a nuclear reactor to cause large numbers of casualties.
    Fact: The containment structure as well as the reactor design for U.S. commercial nuclear power plants make a deadly radiation release, even through sabotage or attack, exceedingly difficult to produce.
  • Myth: Available radioactive sources could be easily blown up to disperse high radiation over large areas.
    Fact: Some recent expert testimony does not address the fact that the effects of a dirty bomb are highly dependent on the size of the radioactive particles produced.
  • Myth: Current federal radiation standards represent safe levels that radiation clean-up must attain.
    Fact: Under current policy, clean-up after a radiological attack would be governed by EPA guidelines --guidelines which are far in excess of anything justified by health considerations.
  • Description

    Nuclear weapons (such as atomic bombs or thermonuclear bombs) induce nuclear reactions in certain materials--materials less radioactive than the products of the reactions. This produces large energy releases along with radioactive daughter products more radioactive than the original material. In contrast, radiological weapons disperse material that is already radioactive. In such weapons there is no energy release from nuclear reactions and no increase in radioactivity.

    This means that in order for a radiological weapon to disperse large amounts of radiation, it must contain highly radioactive material to begin with. Consequently, such weapons are very dangerous to work with and relatively easy to detect--by remote detection of radiation--although the ease of detection depends on specific properties of the radioactive material.

    Radiological weapons are generally not effective weapons, as will be seen. A few countries have pursued the development of radiological military weapons, only to abandon these efforts in favor of more practical and effective weapons. By 1953 the USSR developed a radiological warhead for the R-2 ballistic missile, which was retired as nuclear warheads became available. In 1987 Iraq pursued development of a radiological weapon, but this was discontinued as Iraq concentrated on chemical, nuclear, and biological weapons programs.


    Some radioactive materials pose a limited threat because of relatively low activity levels. Low-level nuclear waste, such as that generated by hospitals and industry, is found at many locations. However, the radioactivity in such waste is not concentrated enough to pose much practical health risk. Indeed, much of this material likely poses greater chemical or biological risks than radiation risks.

    This also applies to some fissile material. Fissile material is material capable of undergoing nuclear chain reactions; in different forms, it fuels nuclear reactors or nuclear weapons. Enriched uranium does not pose a significant risk. Plutonium is a greater concern. However, such material is tightly guarded since in sufficent quantities it could be used in a nuclear weapon.

    Possible radioactive source material includes commercially used isotopes. These are generally found in small quantities, except for source manufacturing sites where controls are stricter.

    High level nuclear waste, such as spent fuel, is unlikely to be used. Such material is hard to obtain, hard to work with, and hard to hide. Security for spent fuel is significant and has been for years, given the fact that it contains fissile material useful for nuclear weapons. Additionally, the safeguards that are used to deal with the hazardous nature of such waste makes theft difficult.


    The factor of the effectiveness of dispersing radioactive material has been poorly addressed by much recent testimony.

    Radioactive material in the form of very small particles or vapor will disperse more outdoors, diluting any effects. Very large particles will not travel far from the point of dispersion. It has often been asserted that "dirty bombs" are relatively simple to devise. This ignores the technical challenge of devising a weapon that will produce an optimum particle size resulting in an effective weapon.

    Consider the dispersion of material by the Chernobyl nuclear accident. Only about 5% of the radioactive inventory of the reactor was released into the atmosphere: about 12,000,000 curies was released in the initial explosion and another 40,000,000 curies by the fire during the next 9 days. (In contrast, a 20-kt nuclear explosion results in radioactive daughter products with radioactivity of 600,000,000 curies one minute after detonation and 5,000,000 curies one hour after detonation.)

    Spent nuclear reactor fuel rods contain thousands to millions of curies of radioactivity, but these are too dangerous handle and are kept under high security anyway. Some cobalt rods used in industrial applications contain 10,000 curies; such rods have been cited as illustrative sources for radiological weapons.

    Biological effects

    In the short term, radiation exposure of sufficient levels can cause radiation sickness or death. In the long term, radiation exposure may increase the risk of various types of cancer.

    Some specific isotopes pose a particular health risk. Biological processes tend to concentrate certain chemicals in certain organs. For example, radioactive iodine, if absorbed into the body, would tend to concentrate in the thyroid gland, causing radiation injury.

    The consequences of some past radiation accidents illustrate the risks. In 1987 a 1,400-curie cesium-137 source was spilled from a discared x-ray machine in a junkyard in Goiania, Brazil. Several people played with the powder, spreading throughout the area. Eventually four people died and about 30 others suffered radiation injuries. Similar but less severe accidents occurred in Mexico in 1983, Turkey in 1998, and Egypt in 2000. Contaimination and injury were so severe, in part, because the radiation release went unrecognized for so long and often because people involved took the material into their houses. One fatality from the Goiania case was a young girl who rubbed the cesium all over her body. Thus even though these were accidents, not intentional attacks, they involved circumstances which permitted doses to accumulate over a longer period of time--circumstances unlikely for a radiological attack. While a radiological weapon would likely involve a more effective means of dispersal, the release is unlikely to go undetected for any significant period of time. Still, such cases do demonstrate that the potential of prompt radiation casualties cannot be excluded.


    If a radiological attack occurs, the response will be seriously hampered by the lack of public education and the lack of civil defense efforts. The American public is not merely uninformed, but misinformed regarding radiation, its effects, and methods of protection. Given current concerns about nuclear terrorism, it is unfortunate that public authorities have not seriously attempted to correct this.

    Current plans apparently assume the application of Environmental Protection Agency (EPA) standards for clean-up of contamination. These standards will result in massive unnecessary economic impact. Consider that EPA standards are 30 times stricter than those for civilian radiation workers, 100 times stricter than the threshold for detectable long term effects, 10,000 times stricter than the threshold for short term effects, and 100 times stricter than the standards applied at the Chernobyl site.

    In fact the EPA's standards are unrealistic: they fail to realistically appraise radiation risks relative to other risks; they apply an unjustifiably higher standard to radiation from manmade sources than from natural sources; and they ignore current understanding of radiation hormesis. Revised standards may be forthcoming from the Department of Homeland Security, but even these will not settle the issue.


    © 2002-2003, 2005 by Wm. Robert Johnston.
    Last modified 15 September 2005.
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