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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

A: 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

A: 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 www.cns.miis.edu), 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

A: 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

A: 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

A: 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

A: 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

A: 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

A: 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

A: In general, the Federal Emergency Management Agency (FEMA) guide and the Department of Homeland Security's www.ready.gov 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

A: 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 www.cns.miis.edu), 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

A: 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.

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