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Dirty Bomb: Expert Q&A

For a week following the February 25, 2003 broadcast of NOVA's "Dirty Bomb," Charles D. Ferguson, an expert on radiological and nuclear terrorism at the Center for Nonproliferation Studies, answered questions concerning the threat of bombs laced with radioactive materials. 


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Q: Is the recent advice to stock up on duct tape and plastic sheeting of any real use in the event of a dirty bomb attack? Would this actually provide any real protection against radioactive dust? Anonymous

Duct tape and plastic sheeting could provide some protection against radioactive dust depending on the source of the radiation and the circumstances of the event. However, there are more important things to consider initially. First, if you are very close to the blast, it would make sense to evacuate the area. In this case, listen for instructions from the authorities. Second, depending on the radioactive source, the radiation could pose an external hazard. For instance, gamma radiation could easily penetrate plastic sheeting. However, for alpha radiation, plastic sheeting could provide adequate blocking protection as long as there is a tight seal. Of course, you would not want to remain in a tightly sealed room for a long time (more than several hours or a day or two). But depending on the circumstance, a radioactive cloud would pass through an area quicker than that. The three principles of radiation protection are: time, distance, and shielding. Minimize the time of exposure. Maximize the distance between you and the radiation source. Maximize the amount of shielding between you and the source.

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Q: I am a high school history teacher. My question is often brought up by many of my students. What steps have been taken by the United States to protect its population against the threat of a dirty bomb? Do you think that people living in metropolitan areas are at higher risk for a possible attack? Anonymous

After September 11th, the U.S. government stepped up its efforts to secure highly radioactive materials. These efforts include issuing advisories to licensees of radioactive materials, sweeping up disused radioactive sources using a Department of Energy program, finding and securing "orphan" sources (those lost, stolen, or abandoned) using a program among the Nuclear Regulatory Commission, Department of Energy, and the Environmental Protection Agency, and increasing inspections of facilities containing radioactive materials. Nonetheless, more support of these programs is needed. In answer to the second part of your question, probably people in metropolitan areas are at higher risk. Because dirty bombs would be intended to frighten a lot of people and shut down parts of our economy, terrorists would tend to target highly populated areas such as cities.

Q: If the release of radioactive materials in a dirty bomb is so "silent," how do we know that it has not been done already? According to the NOVA special, a firecracker could contaminate D.C.'s metro. Elizabeth
Washington, D.C.

In theory, there could already have been a terrorist release of radioactivity that went unnoticed because a radiological dispersal device (RDD) would not even require a bomb blast (even a firecracker) to disperse material. In principle, an RDD attack could be very silent. However, I would tend to discount that this has occurred. First, terrorists typically and traditionally have wanted a lot of people to know immediately of an attack. By definition, the terrorists want to instill terror and the best way to do that is to get immediate attention. Second, the government has been installing radiation detectors in critical areas, so unless the government has hidden the news from us (which would be difficult to do in our society), authorities would likely have detected such a silent RDD attack.

Q: What would be the results if a terrorist put radioactive material in a large city water supply? Richard Fulton
Kincaid, IL

If you don't mind, I'll quote directly from the report on dirty bombs that I wrote with Tahseen Kazi and Judith Perera: "Because contaminating large water supplies to levels beyond acceptable health limits would require an enormous amount of radioactive material, this method is not likely to succeed. Moreover, certain radioisotopes, such as Pu-238 [plutonium-238], are not even water soluble and would tend to sink to the bottom of reservoirs, thereby presenting an essentially insignificant danger to human health." - "Commercial Radioactive Sources: Surveying the Security Risks," Occasional Paper No. 11, Center for Nonproliferation Studies, p. 19

Q: In the event that a dirty bomb does go off (understanding the volume of cesium released would be virtually unknown):

  1. What proximity to the site of explosion would people need to be to warrant a valid medical concern, i.e., where you would recommend they seek medical testing?
  2. Is there any reason to even test such areas for contamination if the radiation levels are, indeed, as low as this program suggested?

Carolyn Collins
Dallas, TX


  1. There are a lot of hypothetical situations to consider. I would not want to speculate as to proximity versus medical concern. I would advise listening to emergency response officials. It is likely that they would take prudent steps to ensure that people are being properly monitored.
  2. Even if there are no immediate health concerns, there can be significant land contamination that could lead to long term health effects if the contamination is not identified and cleaned up. So, testing for contamination would take place even if the threat to public health in the near term would be small.

Q: I spend a great deal of time on the freeways of the Bay Area. What should my response be to a broadcast announcement of a dirty bomb released in a specific area that I was about to pass through in, say, the next 10 minutes? Jim Quinn
Oakland, CA

If I were in your position, I'd not drive through that area. This is just a prudent response. There might not be an immediate health hazard. However, it is likely that once that announcement is broadcast, many people will try to flee that area, so the roads near there would be tied up, preventing you from going there anyway.

Q: In the event of an incident that involves the detonation of an explosive device of unknown nature somewhere in the country, are our local, state, and federal authorities prepared at this time with sufficient procedures, equipment, and personnel to determine whether, in fact, it was a dirty bomb that spread radioisotopes or simply a conventional explosive? Will there come a time when all explosions, accidental or otherwise, will be checked for radioactive material dispersal? Jonathan F. Kotas
Moorpark, CA

Federal, state, and local officials are still far from being fully prepared to know how to respond effectively to such an attack. Nonetheless, at the federal level, the Nuclear Emergency Search Team (NEST) can make the types of determinations you're talking about. NEST can reportedly deploy to anywhere in the U.S. within a short time period. More and more local emergency responders are equipping themselves with radiation detection gear. However, my concern is that these responders should be getting adequate training for operating the equipment. There is some coordination among federal and local officials to provide the equipment and training, but based on what I've seen, there is not enough coordination between local and federal officials.

Q: How serious is the threat of this happening in our country? Should we really be worried, or is this threat far beyond the realm of possibility? We have yet to see it used anywhere. Anonymous

Other than the incident reported in the NOVA program "Dirty Bomb," when Chechen rebels placed unreleased radioactive cesium in a Moscow park, there have not been any dirty bomb events or explosions. However, we now find ourselves in a heightened state of alert about all sorts of threats. Although I cannot quantify how likely it is that there would be a dirty bomb event in this country, I feel that even if there were such an event, it would typically not lead to many deaths from radiation. The conventional bomb blast might kill a lot of people. The use of radiation would tend to scare people. I would encourage our government to do a better job at conveying the message not to panic in the case of a dirty bomb attack.

Q: Our legislature is studying the possibility of allowing Envirocare of Utah to bring millions of tons of Class B and C radioactive nuclear waste to Utah by way of the nation's railroads. I worry that this may provide a real opportunity for terrorists to use rail cars as low-tech dirty bombs. A van filled with explosives under a rail overpass could spread deadly radioactive material over a huge area. A derailment caused by terrorists over a major river could spread for hundreds of miles. What do you think? Seems extremely dangerous to me. Michael Ernsten
West Valley City, Utah

I understand your concern. However, based on what I've heard about the security of the transports, I feel reasonably confident that this does not pose a significant danger. I'm more concerned about the radiation safety and security risks of people holding on to their disused radioactive sources rather than properly disposing of them in facilities such as Envirocare. Our nation has to do a better job at securing and properly disposing of disused sources.

Q: Would firefighters' personal protective equipment (bunking gear and SCBA or APR) protect them from beta radiation? Both low and high energy?

What types of instrumentation would you recommend, and with what sort of dose range capability, for first response and initial surveying at an R.D.D. incident?

At what point, in mR or R, would you establish a "nobody goes beyond here, even for rescues" line? Edwin J. Peterson
Seattle, WA

At the mRem/hour (1/1000 of a Rem per hour) level, there is really not much of a concern for emergency responders. This is a low level. At the Rem/hour level, precautions should be taken. But emergency workers can still operate in that area for a reasonable period of time, say an hour or so without exceeding regulatory limits for radiation workers. Not until the radiation level goes up to tens or hundreds of R would emergency responders have to significantly shorten their time in the area to a very short period, perhaps a few minutes depending on the radiation level. However, it is very unlikely that the typical dirty bomb would generate radiation levels this high.

Q: The NOVA program makes it seem that all cesium chloride (CsCl) is radioactive. Could you confirm that this is not true and that CsCl does indeed come in a stable, non-radioactive form? Anonymous

You're correct. Only the CsCl containing radioactive cesium, such as the isotope cesium-137, would be radioactive. CsCl can also come in non-radioactive forms.

Q: Is it possible to wear some sort of over-the-counter mask to protect yourself in the event of a dirty bomb that contained cesium-137? Probably not since it can be absorbed through the skin, right? Anonymous

There has been a lot of talk about the over-the-counter N95 masks, which are designed to be 95 percent effective at blocking 0.3 micron and larger sized particulates. In the case of Cs-137, an N95 mask might be able to provide some protection against inhalation of the matter; however, Cs-137, because it emits gamma radiation, is also an external health hazard. It also tends to bind to materials such as concrete. So, better advice would be to stay away from the immediate area of a dirty bomb blast. Minimize the time near the area. Maximize the distance between you and the source of the radiation. Place as much shielding, such as dense buildings, as possible between you and the contaminated area.

Q: What would happen if someone tried mixing different sources of radiation to make one huge dirty bomb? Would it be possible to mix cesium-137 with other radioactive material? Anonymous

Yes, this is possible. I could imagine someone trying to maximize both internal and external health risks, so they might combine alpha-emitting and gamma-emitting sources of radiation.

Q: After viewing the NOVA program I am thinking about purchasing a general purpose Geiger counter for home protection. Since I know nothing about this subject, I was wondering if you could suggest a particular product, something easy to use that does not require frequent calibration. I presume calibration requires sending the product back to the manufacturer. Products I have viewed on the net have capability to measure alpha, beta, gamma, and x-radiation, and I wonder if this is sufficient for my protection, should something happen in my area. Bob
Santa Clara, CA

If you and your family would feel safer with the purchase of a Geiger counter, then by all means buy one. However, I'd strongly recommend taking the time to learn how much background radiation is in your area. I would not want you to become overly concerned if you hear clicking when you first turn on the device. As you saw on the NOVA show, when my colleague Andrew Karam turned on a Geiger counter, it registered radiation. This is just normal background radiation. Since I work for a non-profit educational institute and because I have not studied particular product lines, I would not feel comfortable advising which product to buy.

Q: I enjoyed the "Dirty Bomb" episode of NOVA. I found it interesting that cesium chloride can be found on eBay ( eBayISAPI.dll?ViewItem&item =3210448041&category=413). In this form, can it be used in a bomb? Matt Smith
Anchorage, AK

Thanks for the interesting question. I checked out the eBay URL that you listed. Based on the description at that Web site, it is unclear whether the cesium that is being sold through eBay is a stable (non-radioactive) isotope or a radioactive isotope, such as cesium-137. Of course, this does raise the question of verifying the legitimacy of purchasers of radioactive materials. In the U.S., possessors of radioactive sources are required to obtain a license from either their state (if it is part of the Agreement States system, which includes 32 out of the 50 states) or the Nuclear Regulatory Commission.

Q: In regards to securing radioactive materials around the world that could be used in nuclear weapons, do you agree with Graham Allison that securing such materials is "doable?" If so, what are the primary objectives, including immediate steps that need to be taken by the U.S. and other countries and a realistic time frame? Do you consider nuclear materials to be the greatest threat to mankind and this planet and, if so, why do you think elimination of this threat isn't our number one priority? Your article, "Commercial Radioactive Sources: Surveying the Security Risks," lists numerous activities that can be pursued to reduce risks associated with nuclear materials. To what extent are such activities ongoing or being considered by the current Administration? Thank you. Anonymous

Yes, I absolutely agree with Dr. Allison that securing radioactive materials is "doable." The study that I co-wrote and that you refer to lists, as you said, "numerous activities that can be pursued to reduce risks associated" with these materials. First, it is important to keep in mind that not all radioactive materials require a high level of security. Only a small fraction of the millions of radioactive sources in use would require high levels of security, because only these materials could fuel a potent dirty bomb. Many of the security activities discussed in my and my co-authors' study have been initiated by the current Administration. Mainly, the Administration needs to make these efforts a high priority. To a significant extent, those officials in the Administration I've talked to are trying to make this effort a high priority. Concerning additional security steps for these materials, regulatory agencies, other government agencies, and the radioactive source industry should work together to develop an integrated, layered defense system. Concerning a significant security gap noted in the "Commercial Radioactive Source" study, the Nuclear Regulatory Commission is very much aware of the shortcoming in export control systems that we point out in our report. In fact, the NRC is working on tightening export control regulations in the near future.

Concerning nuclear materials, such as highly enriched uranium and plutonium, which could be used in nuclear weapons and which are different than the commercial radioactive sources discussed above, the U.S. and other countries should prioritize securing, reducing, and eventually eliminating such materials to prevent terrorist use. Currently, Dr. William Potter and I are leading a new study of what exact steps should be taken to accomplish the goal of keeping nuclear weapons-usable material out of the hands of terrorists. We intend to publish this study later this year.

Q: I certainly was enlightened as to the threats from dirty bombs based on viewing the NOVA special. As there is so much missing material in this country and certainly an abundance of uncontrolled or missing material worldwide, it is obvious that somewhere, someplace terrorists will obtain (or have obtained) material relatively easily.

Since dirty bomb construction is relatively easy and the threat may be more psychological than physical based on the Brazilian problem, don't you believe it is a foregone conclusion that one or more of these devices will be used in the world somewhere? How do we prepare and educate the populous? I think chaos is our worst enemy if one of these events happens. I think the NOVA special is an excellent start, and maybe all the broadcast/cable networks should run this episode as a community service. Thank you. Anonymous

Thank you very much for raising the important point about educating the public. As you realize, this is a very challenging task. Nonetheless, I and others in the field believe that this should be done. However, because nuclear issues are rife with controversy, we really need to first identify credible and trustworthy experts who can convey to the public that dirty bombs are typically not going to result in major harm to human health. Because we have never actually experienced a dirty bomb event, it is difficult to know how the public will react. However, if there's only one message that I could convey to the public, it is: "Don't panic." I realize the psychological impediments toward getting this message across. Nonetheless, I feel that we have to start addressing it before a dirty bomb explodes.

Q: Discussions in a forum I participate in have stated that a dirty bomb is best described as a "weapon of mass annoyance," as the radiological exposure effects to any individual not in the immediate area of the blast is minimal at worst. For those in the immediate vicinity, the blast effects overshadow the radiological.

The effects would be in panic among folks who got their concepts of radiation from 1950's "B" movies, and in decontamination of equipment and real estate. What are your thoughts on the subject? Dave Neil
Rigby, ID

In general, I agree with you. The NOVA show made the point that dirty bombs are not weapons of mass destruction (such as nuclear weapons) but are weapons of mass disruption. However, I feel that "annoyance" does not really do justice to capturing the "disruption" that could occur. Yes, the health effects are likely to be minimal. However, the contamination would be real and would have to be cleaned up. Determining the level of cleanup would probably be very contentious. But still the cleanup would likely be expensive. So, this prospect is more of a concern than just an annoyance.

Q: As a nonproliferation expert, why didn't you make the distinction between the levels of risk to the public posed by gamma and beta radiation? I felt the NOVA program sensationalized the actual risks associated with a dirty bomb as compared to the "everyday" radiation risks the population is exposed to (e.g., smoking, radon, medical treatments, etc.) If you are a scientifically minded person, is it not beneficial to inform the public that smoking cigarettes can deliver a concentrated dose to the respiratory system of a few Rem per year, while a dirty bomb would deliver a whole-body dose of a few millirem at most? I agree that the economic impacts of urban contamination could be vast, but I feel you exaggerated the human consequences. Thank you. Anonymous

Thanks for the important questions. Unfortunately, the show was only an hour long. Although NOVA covered much useful information, a lot of valuable information was left on the editing room floor; however, I'm reasonably confident that the filmmakers would have included the information you mention in your questions if they had more than an hour for the film length. During my interview with the filmmakers, I discussed many of the points that you raised. In particular, I mentioned that on average about 20 percent of the population will die from cancer. This substantial subset of the population would develop cancers from many causes, such as smoking cigarettes. I also mentioned during the filming that the typical dirty bomb attack would likely lead to a very slight increase in the risk of developing cancer. To give the filmmakers credit for balanced reporting, they did mention at least a few times during the NOVA show that it is likely that few, if any, people would die in the near term from the ionizing radiation exposure. I feel that the filmmakers also showed that the greatest threat from a dirty bomb is due to the contamination clean up costs and other economic impacts.

However, I respectfully disagree with you regarding your statement "a dirty bomb would deliver a whole-body dose of a few millirem [which is a very low level of exposure] at most." There are many dirty scenarios that would result in whole-body doses much greater than a few millirem. For example, if we assume that the 1987 Goiania, Brazil radiation safety crisis, though not an intentional attack, was a dirty bomb-like event, several people surely were exposed to much more than a few millirem. In fact, four people died from radiation sickness and many more were significantly contaminated. The material involved in this case was several hundred curies of cesium-137. There are some radioactive sources that could be available to terrorists that contain a lot more radioactivity than the Brazilian source described above.

Q: In The Economist Magazine (6/15/02, p. 28), it was stated that for a dirty bomb "decontamination ... from a few to dozens of city blocks ... poses the greatest challenge." Demolition and the effect on business could run into "hundreds of billions of dollars." Do you agree? If a dirty bomb caused an increased level of radiation in a city, would it be necessary to evacuate and demolish the area?

Also, is there a Web site you recommend for guidance on dealing with a dirty bomb or other radiation risk? Thank you. Anonymous

Factoring in the costs of demolition and reconstruction, I would not be surprised if the costs could soar to hundreds of billions of dollars, especially if the real estate is in Manhattan, for example. Depending on the radiation level that remains after decontamination efforts were attempted, it may be necessary to evacuate the area.

Regarding Web sites, the government has recently launched, which has some useful textual information about dirty bombs. In general, this Web site is correct to point out the three principles of radiation protection: time, distance, and shielding. Minimize the time in the contaminated area. Maximize the distance between you and the contamination. Maximize the amount of shielding, such as dense buildings, between you and the contamination. I am concerned, however, that some of the cartoon-like illustrations on that Web site give a false impression of the severity of a dirty bomb. In particular, there is an illustration that implies that a substantial part of the state of Texas could be contaminated by a dirty bomb. This is incorrect. Dirty bombs would be far less damaging.

Q: I understand that potassium iodide (KI) should be taken to protect the thyroid in the case of radioactive iodine release with a nuclear emergency. Because there is so little time to respond after a "dirty bomb" or nuclear emergency, it seems it would be wise to take a potassium iodide tablet after an explosion to be safe, rather than wait the hours that may be needed to assess the type of radioactive material that is released. By then it would be too late to do anything. What is your opinion of this? Barbara Smith
Austin, TX

I understand the concerns about potential health hazards. However, I would caution against overuse of KI. It is unlikely that a dirty bomb would contain radioactive iodine. Other more prevalent and dangerous radioactive materials would probably be used in a dirty bomb. There would probably be sufficient time for response officials to analyze the radioactive materials and determine whether radioactive iodine is present. So, I personally would not rush to take KI immediately after an explosion.

Q: We have a cancer center here in town. I live one mile away. They have two linear accelerators there. What would happen if a terrorist walked into the center and blew the accelerators up while they were on? Jeffrey Ross
Muskegon, MI

Linear accelerators are not useful for dirty bombs. If a terrorist blew up the accelerators, there would be damaged equipment, but there would not be a radiological dispersal crisis. If the power is turned off, an accelerator cannot produce radiation. The bomb blast would almost assuredly turn off the power to the accelerators.

Q: If there are devices, as we have seen, that can detect even small amounts of radiation from a vehicle such as a helicopter, then why can't the Georgian government use this technology to try and track down the missing generators from the lighthouses that the NOVA program described? Anonymous

Yes, radiation detection equipment as you described can be used to track down the missing generators. However, in my discussions with Abel Gonzalez of the IAEA, I've found out that such searches can be very expensive and time consuming. In addition to the mission described on NOVA, there have also been other successful IAEA- and Georgian government-sponsored missions to track down radioactive materials in Georgia. Last year, the IAEA, the U.S. Department of Energy, and the Russian Ministry of Atomic Energy renewed efforts to track down these highly radioactive materials. Such searches could be accelerated if Russia is able to release and/or find records of where these materials may be located. The bottom line is that the IAEA, the U.S., and Russia are seriously working on this problem. We have to make sure that this work remains a high priority.

Q: I am a health physicist here at the University of Miami's Medical Campus. The NOVA broadcast brought up, in the Brazilian example, the problem of overwhelming the health system. But it did not answer the question of how to avoid overwhelming our health-care facilities with people who are "worried well" about future events. How should we plan? Any response would be greatly appreciated. Thank you. Sam Iverstine
Assistant Rad. Safety Officer
Coordinator for Mass Radiological Events
University of Miami

Mr. Iverstine, I would have to defer to your expertise in this area. I have been working in nonproliferation and security studies and have not focused on the health-care system. I would strongly urge that likeminded radiation safety officers come together to help public health and other health-care officials determine how to deal with the issue that you raised. I am aware that the Health Physics Society (HPS) has been examining issues related to this, as you probably know. So, I would advise working with HPS and health-care officials to try to deal with this issue.

Q: In the NOVA "Dirty Bomb" episode, the experts talked about radioactive substances scattered all over the former Soviet Union and that Russia has forgotten their locations or has failed to recover these substances, leaving them as an easy capture for possible terrorist "dirty bombs." Would it be conceivable that a satellite with either thermal or some other way could take images revealing these high concentrations of unrecovered radioactive substances, which could then perhaps be retrieved by a United Nations task force in this field? Or is this inconceivable due to funding, technology, foreign relations, or some other reason? Evan
Lincolnshire, IL

This is an interesting question. The IAEA and various governments have used helicopters equipped with radiation detectors to track down radioactive sources in the former Soviet Union. However, I'm not aware of any efforts to use thermal imaging satellites as you suggested. Perhaps this is underway. I suspect, though, that it may be difficult to discriminate the thermal signal from highly radioactive sources from other non-radioactive thermal sources.

Before investing funds in this method, I'd suggest that scientists with expertise in thermal imaging satellites calculate whether these satellites could unambiguously detect these signals. The signal would depend on what type of radioisotope is in a source and how much of the isotope is present in the source. In addition, the thermal image produced would depend on the interaction of the radiation emitted by a radioactive isotope with surrounding matter. All these factors should be taken into account in determining whether such satellites could help track down these radioactive materials.

Q: What radioactive material or sources pose the greatest threat for use in a Radiological Dispersion Device, based on the inherent radiological risk and on their relative availability? That is, over what sources in U.S. commerce is greater security and oversight most urgently needed? Thor Strong
Lansing, MI

In the recently published report "Commercial Radioactive Sources: Surveying the Security Risks," Occasional Paper No. 11, Center for Nonproliferation Studies, by myself, Tahseen Kazi, and Judith Perera (available at, we describe the top seven radioisotopes that if present in large enough amounts in a radioactive source would pose inherent radiological security risks. These radioisotopes are americium-241, californium-252, cesium-137, cobalt-60, iridium-192, plutonium-238, and strontium-90. These are all produced in nuclear reactors. In addition, we would include radium-226, a naturally occurring radioisotope that has been widely used throughout the world.

Concerning U.S. export control and licensing rules for these materials, radium-226 because it is naturally occurring is not subject to the licensing rules governing the reactor-produced radioisotopes. For the other radioisotopes, except for certain restrictions on plutonium, americium, and californium, essentially unlimited amounts of the other isotopes can be exported to almost all countries (except those such as North Korea, Iran, and Iraq that are under embargo). The licensing rules are such that there are requirements for a detailed governmental review of the credentials of end-users. After our report was published, we briefed some government officials about this loophole. They are aware of it and are taking steps to tighten the regulations.

Citizens should encourage their elected officials to become more engaged in securing the high priority radioactive sources. Currently, there are three bills before Congress that deserve support. First, Senator Hillary Rodham Clinton and Senator Judd Gregg have reintroduced legislation called the Dirty Bomb Prevention Act of 2003. This bill aims to establish a task force consisting of senior government officials charged to determine how best to secure radioactive materials. Rep. Edward Markey is sponsoring a similar bill in the House of Representatives. Second, Senator Richard Lugar, Senator Joseph Biden, and Senator Pete Domenici are close to reintroducing legislation from last October that would focus more on the international dimension of radioactive source security. Third, Senator Mary Landrieu has introduced legislation to provide for increased port security. I urge Americans to contact their congressional representatives to support these pieces of legislation.

Q: Would not the radioactive storage room of a hospital or nuclear lab be the perfect place to keep a dirty bomb until ready for use? Sherlock Holmes once said that the perfect place to hide a book was in a library. If I were the FBI, I would be doing background checks on all employees with access or delivery to such places. Anonymous

That's an interesting observation. Could there be a "rogue" element at these facilities surreptitiously building dirty bombs? Owners and operators of these facilities are required by federal regulation to conduct regular inspections and ensure that their facilities are secure. It is my understanding that the Nuclear Regulatory Commission is considering background checks for the highest risk facilities. The NRC has been coordinating security activities with the FBI, but I'm not sure if the FBI is conducting such checks.

Q: Comparing the dirty bomb with the depleted uranium that has been extensively used by the U.S. in Kosovo, Bosnia, and Afghanistan, which one is more dangerous from the standpoints of chemical poisoning, radiation-caused diseases, and half-life? Jim
Charlotte, NC

Depleted uranium would not be an effective material for a radiological dirty bomb because it has a very long half-life and is not very radioactive. There are several other radioactive materials that pose higher radiological security risks. Nonetheless, because depleted uranium is a heavy metal, it could present a chemical poisoning risk in large enough doses, especially to the kidneys.

Q: In the event of a "dirty bomb" detonation, is there any program or resources available to citizens to predict the path of the fallout? Would it be possible to calculate the rads per minute as the cloud progresses based on, perhaps, government or university sensors, initial radiation readings, etc.? Thank you. Anonymous

Lawrence Livermore National Laboratory has developed a computer code called HOTSPOT, which is available for free on the Internet. This code can be used to get a rough estimate of the amount of contamination, the plume (cloud) progression, etc. Government officials can use computer tools such as HOTSPOT to determine quickly what emergency steps should be taken. More sophisticated modeling codes can be used to make more accurate determinations of contamination in the intermediate to long terms. Citizens if they are so inclined could learn to use HOTSPOT, but I feel that it makes the most sense to listen to authorities, because they will have the equipment to determine quickly and in sufficient detail where plumes are headed and what type of radioactive material is involved.

Q: How is low-level radiation good for your health? Anonymous

Thank you for your question. Answering it gives me an opportunity to refute the notion that I may have appeared to endorse on the NOVA show the idea of a hormesis effect. Hormesis posits that exposing people to low-level doses of ionizing radiation greater than the inescapable background radiation will lead to health benefits. Based on my readings of this subject, I believe that this notion mainly comes from a false reasoning by analogy. It is known that small doses of certain chemicals, such as selenium, are essential for good health, but large doses are surely harmful. Similarly, proponents of hormesis argue that low-level doses of ionizing radiation stress the body enough to stimulate an "adaptive response," which could result in protective effects for the body. The reasoning by analogy is false because ionizing radiation interacts with living tissue differently than the way bacteria, viruses, or chemicals typically interact with the body.

Health studies—with proper control groups in place and that consider whether the group under study is generally healthier than other populations because of increased access to health care or access to adequate nutrition and exercise—have not shown evidence for a hormetic effect. In sum, there is no clear evidence that low-level ionizing radiation is good for your health. For now, I believe that the safe response is to keep radiation exposure "as low as reasonably achievable," known by the acronym ALARA in the radiation safety field.

Q: What length of time would pass between the detonation of a dirty bomb and the public notification of the event? It seems that it would take some time to determine that radiological material was present in a terrorist bomb attack. Are we prepared to test any and all blast sites for the presence of radioactive material? Scott Nice
Dallas, PA

These are all vital questions. The short answer is that I don't know how long it would take for public notification. The actual response would strongly depend on the answer to your second question. That is, if authorities are prepared to test any and all blast sites for the presence of radioactive material, then they would have the information in a short period of time in order to notify the public. I've read press accounts that emergency responders are gearing up to be able to conduct these tests. But I do not know the actual extent and depth of these efforts.

Q: What solutions/products do you use to clean up radioactive materials? Sorry I missed the show; I learned a lot from the Q&A. Anonymous

Presently, clean up or decontamination is mainly at a low-tech stage—so-called "muck and truck." Techniques include sand-blasting buildings to remove the layers of contamination and removing the layers of contaminated soil and trucking it away. I understand from talking to some U.S. national laboratory scientists that more advanced research and development to find effective decontamination methods are underway. As Michael Levi said on the NOVA program, we really can't eliminate radioactivity; we can only transfer it from one place to another. I would add that then we would have to wait until the radioactive materials decay. For a substance such as cesium-137 with a 30-year half-life, we would have to wait at least six or seven half-lives or about 200 years until the material has decayed to very small amounts.

Q: Do you think there is any value to the Red Cross/government guide to terrorism disaster plans? Is there anything else you recommend we do? Anonymous

In general, the Federal Emergency Management Agency (FEMA) guide and the Department of Homeland Security's Web site provide useful general information that can be helpful for most emergencies, such as hurricanes, tornadoes, etc. In particular, these sources of information usefully discuss the three principles to minimize excess radiation exposure. These principles are time, distance, and shielding. Minimize the time of exposure. Maximize the distance between you and the radiation source. Maximize the amount of shielding between you and the source.

However, the government has to be able to detect ionizing radiation from a dirty bomb in a rapid enough fashion to give people proper instructions as to the particular event. As my colleague Michael Levi has said, smoke detectors in homes help provide the alert system that people need to be able to remove themselves from possible danger in a calm but expeditious manner. Similarly, we need the equivalent of a smoke detector for radiation. Perhaps the government has adequate radiation detectors in place, but I'm not sure.

Q: Cs-137 was illustrated as dirty bomb material in the NOVA special. I understand Cs-137 poses a great threat because of its physical form (powder) and availability, however other isotopes have been widely produced and distributed. Do other easily exploitable isotopes such as Co-60 have the same potential for dispersion, or does the physical form of most of the other exploitable isotopes make wide dispersion unlikely? Additionally if you would name several other isotopes that have high potential to be exploited, it would be very helpful, as I am involved in preparations being made to respond to a RDD. Thank you for providing accurate information regarding this horrible threat. Curtis Liddle
Boston, MA

If you don't mind, I'm copying part of an answer to an earlier question to answer part of your question: In the recently published report "Commercial Radioactive Sources: Surveying the Security Risks," Occasional Paper No. 11, Center for Nonproliferation Studies, by myself, Tahseen Kazi, and Judith Perera (available at, we describe the top seven radioisotopes that if present in large enough amounts in a radioactive source would pose inherent radiological security risks. These radioisotopes are americium-241, californium-252, cesium-137, cobalt-60, iridium-192, plutonium-238, and strontium-90. These are all produced in nuclear reactors. In addition, we would include radium-226, a naturally occurring radioisotope that has been widely used throughout the world.

Concerning the dispersibility of radioisotopes other than cesium-137, cobalt-60, for example, is usually in a solid metal form, so in that form it would be difficult to disperse. However, it is not impossible to make cobalt-60 more dispersible, but in doing so even suicidal terrorists could risk exposing themselves to a lethal dose of radioactivity in a very short period of time. In the report cited above, my co-authors and I recommend that radioactive source producers should strive to make sources that are relatively difficult to disperse. One way to do this would be to reduce the production of powdered cesium chloride.

Q: After watching the program about dirty bombs, I had a question. I live near Lake Michigan, and I was wondering what effect a dirty bomb would have on the ecosystem of a large body of water? What about a pond or stream, and would these bombs eventually effect ocean life? Anonymous

Again, if you don't mind, I'll quote from an earlier answer: "Because contaminating large water supplies to levels beyond acceptable health limits would require an enormous amount of radioactive material, this method is not likely to succeed. Moreover, certain radioisotopes, such as Pu-238 [plutonium-238], are not even water soluble and would tend to sink to the bottom of reservoirs, thereby presenting an essentially insignificant danger to human health." (Source: "Commercial Radioactive Sources: Surveying the Security Risks," Occasional Paper No. 11, Center for Nonproliferation Studies, p. 19.) Perhaps small ponds could become highly contaminated if there is enough radioactive material and if the radioactive material is soluble.

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

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.
Lake Zurich, IL

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

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
Buffalo Grove, IL

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

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
Pasadena, CA

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

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
Hawthorn Woods, IL

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
Buffalo Grove, IL

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:

  1. If science can figure out a way to make a nuclear device, with all its terrible effects, could it not be possible for science to find a way to neutralize a nuclear contaminated area? It would certainly make more sense than removing the contaminated material (earth, buildings, etc), only to deposit the material some place else and contaminate that area.
  2. How about devising something that everyone could wear that could not only detect radiation but also its degree? For example, the face of a watch that, depending on the color it turned, could tell you how strong the exposure was and even, through comparison, locate the epicenter.

Maybe more time and energy needs to be spent on defensive measures than ever before. Dave Katz
Markham, VA


  1. There is no way to "neutralize" radioactivity. The best we can do is transfer radioactive material to some place and then wait for it to decay. As I indicated in a previous answer to a question, decontamination techniques are at a relatively low-tech level; however, advanced research in this area is underway.
  2. If enough people would feel comfortable wearing such devices, then there might be a large enough demand for them to be developed. However, I'm skeptical that people would want to be reminded about radioactivity on a continuous basis. But this may be worth looking into. Thanks for the thought-provoking question.

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
Chelmsford, MA

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
Vancouver, BC, Canada

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: With all the low-grade radioactive materials seemingly lying around in Russia not protected—they don't even seem to know where half this stuff is anymore—are they doing anything about it? Are they trying to find this stuff and get it under some sort of security and compile a list of what they have and what might be missing? And the same here in the U.S., where it doesn't seem to be regulated, tracked, or protected well—will we do the same and try to find out what is missing and track it?

All you hear on the news is possible bioattacks. While those are valid, could terrorists be distracting us with that possibility while actually making dirty bomb plans and catching us preparing for bio and not for the other? What are we doing to protect against and clean up after a dirty bomb? Anonymous

The Russians are starting to work very closely with the U.S. government on this issue. I've heard from American officials that Russian officials are very concerned about the dirty bomb issue and are stepping up efforts to track down these materials and secure them. Nonetheless, a big problem is that records of the locations of radioactive materials were often poorly kept. In general, all countries need to develop confidential, national registries of radioactive materials. Based on discussions with U.S. Nuclear Regulatory Commission officials, I understand that the NRC is starting to develop such a registry in the U.S. The International Atomic Energy Agency (IAEA) is working with many member nations to develop such registries. However, there are many nations (at least 50) that do not qualify for IAEA assistance. So we need to find a way to assist them in developing better regulatory infrastructures. In addition, in the U.S., the Department of Energy, NRC, and EPA have programs that were relatively recently launched to track down "orphan" (lost or stolen) radioactive sources.

We have to prepare for both biological and dirty bomb attacks as well as other types of attacks. The government is starting to become more serious about the prevention of and clean up after dirty bomb attacks. I've discussed some of these efforts in some of the answers to previous questions. One program that I don't think I mentioned is the Department of Energy's Offsite Source Recovery Project. So far, it has secured more than 5,000 disused radioactive sources that could have posed a security risk. There are several thousand more sources that this program intends to secure. We have to make sure that the Administration and Congress provide adequate funds for programs such as this to continue to do its work. We also have to continue to cooperate with other nations in developing effective export and import control laws to ensure that users of radioactive sources are legitimate. In addition, the U.S. should continue to strongly support the work of the IAEA in improving nations' regulatory infrastructures of radioactive materials.

Editor's Notes

This feature originally appeared on the site for the NOVA program Dirty Bomb.