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 Q: Last Saturday Customs officials announced that from now on they will check all travellers arriving in the U.S. for radiation using small radiation detectors. I have two questions concerning this announcement. Do you feel that this step will protect us from terrorists smuggling radioactive materials or a dirty bomb into the U.S., or will we still be significantly at risk? Also, do you think there is a way that a traveler carrying radioactive materials or a dirty bomb could evade detection from inspectors even with the stepped-up screening? Anonymous A: In general, checking travelers for possession of radioactive materials makes sense. It is an important line of defense. However, I would caution against the public or officials developing a false sense of security based on this measure alone. I and others in the field have been recommending a defense-in-depth approach in which there are many layers of preventive, detection, and response measures in order to erect many barriers to radiological terrorism. The more hurdles a radiological terrorist has to jump over to acquire radioactive materials, the less likely he will be able to carry out terrorist activities with these materials. Let's also be cognizant of the fact that smugglers can try to shield radioactive materials. One class of radioactive materials is relatively easy to shield. This is the category of alpha-emitters. Alpha particles can be blocked by a sheet of paper, so not much shielding is required. Therefore, it is relatively difficult to detect alpha-emitters. We also need to make sure that customs and border security officials operating radiation detection equipment receive proper training. I would also recommend combining the use of radiation detectors with the employment of x-ray machines that can detect the presence of heavy, dense shielding. This method would help to figure out whether someone is trying to sneak radioactive materials past radiation sensors. Q: What are the differences between a dirty bomb and a nuclear bomb? Kathleen G. A: The differences between a dirty bomb and a nuclear bomb are profound. A dirty bomb is not a nuclear bomb even though it uses radioactive material. While a nuclear bomb is surely a weapon of mass destruction, a dirty bomb is at best a weapon of mass disruption. Few people, if any, would die shortly after exposure to the ionizing radiation from a dirty bomb. Perhaps many (at most hundreds) would die from the conventional bomb blast associated with a dirty bomb. In contrast, many thousands to tens of thousands of people would likely die from the explosion of a nuclear bomb (assuming one roughly as powerful as the Hiroshima bomb, which was modest compared to modern nuclear weapons). As Dr. Allison writes in the companion essay on this Web site, he has "compared the difference between a dirty bomb and a nuclear bomb to the difference between a lightning bug and lightning." Q: Are spent fuel pools at nuclear power plants "soft targets" for terrorists? Anonymous A: I would not characterize spent fuel pools as "soft targets." At U.S. nuclear power plants, there are many lines of defense typically between potential terrorists and spent fuel pools. To cause possible offsite release of radioactivity from these pools, someone would have to drain the pools of water; this would be difficult to do. Then he or she would have to ignite the spent fuel. There is ongoing debate about how difficult the ignition would be. Q: How can authorities recognize the difference between a dirty bomb that has released beta radiation and one that has released gamma radiation? Ilya Polyakov A: There are radiation detectors that can determine among different types of radiation. Each radioisotope emits radiation with definite energy characteristics - a fingerprint in essence. Certain radiation detectors can precisely analyze the energy of the radiation. This information can then point to what type of radioisotope was used in the dirty bomb and whether it is an alpha, beta, or gamma-emitter. Q: Are there certain age groups that would be more susceptible to the effects of a dirty bomb than others? Nina A: I'll focus on a well-known example. It is known that radioactive iodine is a health hazard for children. Because children are still growing, their thyroid glands are very active. These glands use a lot of iodine. So radioactive iodine absorbed in the body would tend to accumulate in the thyroid. This accumulation could lead to development of thyroid cancer. If it is suspected that radioactive iodine has been released from a nuclear power plant accident or a dirty bomb, people in the surrounding area are advised to take potassium iodide (KI) in order to flood their thyroids with non-radioactive iodine to block the absorption of radioactive iodine. To be most effective, KI should be taken before exposure to radioactive iodine. However, I believe that it is unlikely that radioactive iodine would be used in a dirty bomb. There are other radioisotopes that are more likely candidates for terrorist use. Q: My question is about the level of preparation for a dirty bomb attack on a subway system such as that in New York. From the show, it appeared that one of the greatest problems associated with such an attack would be the subsequent dispersal of the material and the fact that we would not necessarily know where or how fast contamination was spreading. I am a geologist and am well acquainted with using GIS (Geographic Information Systems) to manage spatial datasets. Digital Geiger counters are fairly cheap, as are many GPS devices. Is there any move to install permanent Geiger counters at, say, the access points in the subway system in New York? Such a system could feed into a database that tracked radiation levels in real time. If there was an attack, we would be able to detect it and shut off air circulation equipment and train service as quickly as possible. We would also be able to track the contaminated plume as it spread. Workers with portable Geiger counters linked to GPS could walk around the region and provide more detailed maps of the contamination. It seems that this type of system would have numerous advantages. If there is an attack, we would acquire information about the dispersal of these materials that is currently very theoretical and that could guide our cleanup efforts. If a project of this sort was made public, the American people would feel much more confident using our transportation system—and in our government's ability to respond to a crisis. You could even allow the measured radiation level to be displayed, which would comfort many people who like to feel like they know what is going on. This may actually deter an attack, since our level of preparedness would negate much of the terror-inducing potential of such an attack. Unfortunately, this may also redirect terrorism towards a less-measureable target. Anyway, this seemed to me like it would be an obvious move for our government to take, so I was interested if you had any information on whether or not we were trying this type of system. Thank you very much. Rowena Lohman A: I don't have any authoritative information that our government is installing the kind of system that you propose. In my opinion, what you propose makes a lot of sense. I've read press accounts that the government has been installing chemical detectors in subway systems, so logically it would make sense to install radiation detectors at the same time. Given the fact that the government implemented a radiation detection system last weekend at all border crossings, I would hope that the government is taking similar measures at high-profile and well-trafficked places such as subway systems. Q: The NOVA program makes the dirty-bomb threat sound dire indeed. But a dirty-bomb attack would be child's play next to an attack using a nuclear device—which, if you believe Graham Allison (which I do), is something terrorist organizations like Al Qaeda have tried to acquire and would very likely use if they had the chance. Shouldn't that horrific possibility worry us far more than the dirty bomb threat? Which do you worry about more? Thank you. Anonymous A: Risk is often defined as a product of likelihood and consequence. I believe that the likelihood of a dirty bomb attack is much higher than a nuclear bomb attack, mainly because of the prevalence of commercial radioactive materials and the relative ease of construction of a dirty bomb. In terms of consequence, however, a nuclear bomb would be much more devastating than a dirty bomb. Multiplying the factors of likelihood and consequence together, it may seem unclear which type of bomb has the highest risk. Because I tend to put more weight on consequence, I worry about a nuclear bomb a lot more than a dirty bomb. A nuclear bomb exploded in an American city or anywhere else in the world by a terrorist would have profound and disturbing repercussions beyond the deaths of perhaps tens of thousands of people. Therefore, we have to do everything in our power to prevent a nuclear bomb attack. Q: It seems that estimates of the number of cancer victims after the nuclear bombs were dropped on Japan were much higher than in actuality. So would a dirty bomb actually cause less damage in the form of cancer to people and more damage by scaring people and putting them in a panic mode, making the situation even worse than it really is? Dana A: The well-known "survivor effect" can explain why there might apparently be fewer cancer victims from the group of people who experienced the nuclear weapons bombings on Hiroshima and Nagasaki. These people were exposed to flash doses of ionizing radiation, especially high-energy gamma radiation. The survivors have in effect been selected for low radiation sensitivity and high immune system strength. So, in this group, we should expect to see people who are less susceptible to developing cancer from ionizing radiation. A dirty bomb is very different from a nuclear bomb. For most dirty bomb events, the health hazard would primarily arise from radioactive contamination. If contamination is not cleaned up, there would be a risk that some people who remained in the contaminated area could develop cancer. Few people, if any, would receive acute doses of radiation in the short term. So people should remain as calm as possible following a dirty bomb event. There would be adequate time to respond to the event in a calm, deliberate manner. As I said in the NOVA show, "It is likely that more people would die from traffic accidents by fleeing the scene than would die from ionizing radiation." So we really have to get the message out to people that panic is the worst response to a dirty bomb. Q: Why has the idea of using a "dirty bomb" as a means of terrorism become so popular in the last 20 years? Could it possibly be because our technology is changing, and terrorists need new and effective weapons in order to be taken seriously? Tom A: We have to be careful about stereotyping terrorists. Only a few groups are apparently inclined to consider using radiological or nuclear terrorism. We know that Al Qaeda, for instance, has expressed interest in these forms of terrorists. To address your first question, there has certainly been a growth of analytic interest in dirty bombs. However, as of yet, there has been no actual dirty bomb explosions. Perhaps this occurrence is inevitable. But fortunately we still have time to prioritize securing the radioactive materials that pose the highest security risks and putting in place other defensive measures. Maybe certain terrorist groups like Al Qaeda are drawn toward using high technology against us, so they may then be inclined to use radioactive materials as terror weapons. Traditionally and typically, most terrorists have wanted a lot of people watching acts of terror and not a lot of people dead. Al Qaeda appears to be the big exception to this observation. Q: Two thoughts:
Dave Katz A:
Q: Given the extreme dangers and the health risks for terrorists in making a dirty radioactive bomb, and the scarcity of available materials for them to use, isn't it more likely terrorists will make dirty chemical dispersal devices? There are plenty of really nasty materials around—for example, cyanide and chlorinated organophosphates, to name but two. These could be made and deployed relatively easily in large numbers. What is being done to defend us against the broader threat of nasty chemicals in general? Mark Shilton A: Only very highly radioactive materials that emit penetrating gamma radiation, for instance, would be immediately life-threatening for terrorists making dirty bombs. As I argue in the report I helped write ("Commercial Radioactive Sources: Surveying the Security Risks," Center for Nonproliferation Studies, Occasional Paper No. 11, January 2003), terrorists may then tend to turn to less radioactive materials or alpha-emitting materials, which do not pose an external health threat. Addressing your question about chemical threats, I agree with you that there are a lot of nasty chemicals, which some terrorists may be inclined to use. Some of these substances could, if used effectively, kill a lot of people. Therefore, these materials may be more hazardous from the health perspective than most radioactive sources that could end up in dirty bombs. So we should ensure that these chemicals are secure as well as radioactive sources that pose high risks. Q: Given moderate exposure to the particulates of an exploded dirty bomb, are there any medical interventions that would lessen the potential for developing cancer from the exposure in the long term? Cul Heath A: Recently, there have been news reports that the U.S. Food and Drug Administration (FDA) has been encouraging companies to develop procedures and substances that could help purge the body of radioactive materials that have been ingested. A prominent recent example is the compound Prussian Blue, which has been used as a paint pigment. Reportedly, Prussian Blue preferentially binds to cesium and thallium. So the theory is that taking Prussian Blue after ingesting radioactive cesium could help flush the body of the radioactive material. Frankly, I'm skeptical that such material would provide much protection. As my colleague Michael Levi recently said, "Perhaps Prussian Blue would be helpful if terrorists force-fed people cesium." Of course, this is farfetched. I don't want to imply that effective medical interventions will not be developed. Nonetheless, I'm cautious because I don't want to give people a false sense of security. I'd recommend developing a healthy skepticism about these medical claims until they are proven. Q:
Anonymous A:
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