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FRANK BARNABY, B.Sc., M.Sc., Ph.D., D.Sc. (Hon.)Frank Barnaby, a nuclear physicist by training, has worked at the Atomic Weapons Research Establishment, Aldermaston (1951-57),...
Dirty bombs
30 Apr, 2009 06:49 pm
The murder of the former Russian intelligence agent Alexander Litvinenko by radioactive poisoning with polonium-210 dramatically brought home the potential risks and effects of the terrorist use of a dirty bomb.
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The Litvinenko murder demonstrated the difficulties of decontaminating people and structures, the problems of the timely detection and identification of any radioactive isotope used in a dirty bomb, particularly if it is an isotope that emits alpha particles. His rapid death demonstrated the very high toxicity of isotopes that emit alpha particles.
According to official estimates of risk, the inhalation of a mere 0.06 micrograms of polonium-210 will cause a fatal cancer. And the ingestion of 0.3 micrograms of polonium-210 will cause a fatal cancer (1).
A dirty bomb, a relatively primitive terrorist nuclear device, would consist of a conventional high explosive (for example, semtex, dynamite or TNT), some incendiary material (like thermite) surrounding the conventional explosive, and a quantity of a radioactive material, probably placed at the centre of the explosive.
When the conventional high explosive is detonated the radioactive material would be vaporised. The fire ignited by the incendiary material would carry the radioactivity up into the atmosphere. It would then be blown downwind, spreading radioactivity.
To date no-one has detonated a dirty bomb, also called a radiological dispersal device. There are, however, good reasons to believe that it is only a matter of time before one is detonated. There is so much radioactive material used around the world that terrorist groups would have little trouble getting hold of some. It could then fabricate a dirty bomb without much difficulty.
According to a recent story on the BBC, officials in the UK Home Office are well aware that the chances of terrorists getting hold of materials for dirty bombs “have increased in a world of failed states, in a world of easy availability of radiological material in hospitals and in a world of greatly increased smuggling of these kinds of materials." British Home Secretary Jacqui Smith has announced a new
There have been two cases of bombs containing radioactive materials - neither was detonated (3). Both involved
In December 1998, the Chechen Security Service found a container filled with radioactive materials attached to an explosive mine hidden near a railway line about 10 miles east of the Chechen capital of
A dirty bomb is not the same as a nuclear weapon in the normal sense of the phrase. A nuclear weapon obtains its explosive power from nuclear fission. A dirty bomb involves no nuclear fission, its explosive is a conventional one.
Many types of radioisotopes (radioactive isotopes) could be used in a dirty bomb. But the most likely one to be used is one that is that is relatively easily available, has a relatively long half-life, and emits energetic radiation. Potential candidates include caesium-137, cobalt-60, and iridium-192; these emit mainly gamma rays (electromagnetic radiation). Strontium-90, which emits beta particles (electrons) and is concentrated in bone, is another possible choice.
All of these radioisotopes are much used in medicine and industry – all but small hospitals, for example, will have some. The use of plutonium in a dirty bomb would cause the greatest threat to human health, because of its very high inhalation toxicity, and the most extensive contamination.
Plutonium is, however, generally stored securely and terrorists would find it relatively difficult to acquire it. But as more plutonium is used around the world as a nuclear fuel, it will become easier to acquire some.
Authoritative estimates of the amount of weapons-grade plutonium that will, if inhaled, cause lung cancer suggest that the inhalation of about 150 micrograms will cause lung cancer. And it is suggested that the amount of weapons-grade plutonium that will, if ingested, cause cancer is about 200 milligrams (4). As described above, polonium-210 is far more toxic but it is so difficult to acquire it that it is not a likely candidate for a dirty bomb.
The detonation of a dirty bomb is likely to result in some deaths but would not result in the hundreds of thousands of fatalities that could be caused by the explosion in a city of a crude nuclear weapon. Generally, the explosion of the conventional explosive would be the most likely cause of any immediate deaths or serious injuries. The radioactive material in the bomb would be dispersed into the air but would be soon diluted to relatively low concentrations.
If the bomb is exploded in a city, as it almost certainly would be, some people are likely to be exposed to a dose of radiation. But the dose is in most cases likely to be relatively small. A low-level exposure to radiation would slightly increase the long-term risk of cancer.
The main potential impact of a dirty bomb is psychological – it would cause considerable fear, panic and social disruption, exactly the effects terrorists wish to achieve. The public fear of radiation is very great indeed, some say irrationally so.
The explosion of a dirty bomb could result in the contamination of an area of a city and the surrounding areas with radioactivity. Areas as large as tens of square kilometres could be contaminated with radioactivity to levels above those recommended by the Health Protection Agency for the exposure of civilians to radioactivity (5). The area would have to be evacuated and decontaminated. Decontamination is likely to be very costly (costing millions of pounds) and take weeks or, most likely, many months to complete.
There are no ways to decontaminate effectively buildings contaminated with significant amounts of radioactivity; the buildings may, in practice, have to be demolished. If a dirty bomb were detonated in, for example,
To effectively counter nuclear terrorism it is important to prevent terrorists from acquiring significant quantities of radioisotopes, particularly caesium-137, strontium-90, cobalt-60, and plutonium to build a dirty bomb. The protection of these radioactive materials is clearly of the utmost importance.
There are literally millions of radioactive sources used worldwide in medicine, industry and agriculture; many of them could be used to fabricate a dirty bomb (6). They are often not kept securely (7).
We are moving into a world of the nuclear renaissance, in which there will be a large increase in the global use of nuclear power for electricity generation. In this world, there will be an increased risk of nuclear terrorism.
It is very odd that a dirty bomb has not yet been exploded. We must expect that one will.
References
3. Dirty Bomb, NOVA Public Broadcasting Service.
www.pbs.org/wgbh/nova/
4. Fetter, Steve and von Hippel, Frank, The hazard from plutonium dispersal by nuclear-warhead accidents, Sci. Global Security, 1990, Vol.2, 21–42
and
US National Research Council Committee on the Biological Effects of Ionizing Radiation (BEIR), Health Risks of Radon and Other Internally Deposited Alpha-Emitters (BEIR IV), National Academy Press, Washington DC, 1988, p. 177.
www.iaea.or.at/Publications/Booklets/SealedRadioactiveSources/pdfs/fs_radioactivity.pdf
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Comment by Living Live
1 May, 2009 12:47 pm
Scary Stuff
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