COMING CLEAN ABOUT DIRTY BOMBS
Dirty bombs present some risk to humans and a huge risk of widespread economic disruption. The threat can be mitigated with today’s know-how, but it will require new thinking, new focus and some money.
A dirty bomb is essentially a conventional bomb packaged together with a quantity of radioactive materials. When exploded, the dirty bomb disperses its radioactive material as dust over a wide area. The impact (in addition to the explosives-related damage) is widespread radioactive contamination that might result in equally widespread disruption of life over a wide area, as well as some health hazards.
Concern about dirty bombs is high among security professionals because:
the bombs do not require specialized know-how, expertise or technologies;
there is proof that terrorists around the world are working to deploy dirty bombs; and
efforts to mitigate and defend against the threat of dirty bombs are at an embryonic stage.
The good news is that it is possible to establish basic defenses against dirty bombs rather fast. Most of the necessary technology is available, even some of the products, and it is very much a matter of priorities, planning and execution.
Sources of radioactive materials
In the industrialized world there are thousands of clinical radiotherapy centers and radioactive sterilization sites, both of which use very high doses of radioactive sources. Most hospitals, research labs and many manufacturing processes could be a source for radioactive material for use in a dirty bomb (e.g., gamma sources used for nondestructive testing of welding in shipyards and the pipe welding industries).
The most harmful sources of nuclear waste are, of course, in the nuclear industry (power and weapons). Fortunately, these facilities are relatively well protected. But the level of protection and permeability of security vary wildly among locations and countries (e.g., the former Soviet Union).
Terrorists know how easy it is to get material for dirty bombs, and they have been busy trying to assemble them. Intelligence agencies and nuclear non-proliferation agencies are well aware of vulnerabilities and the efforts to exploit these vulnerabilities. As of Dec. 31, 2001, the International Atomic Energy Agency had confirmed 17 incidents of illicit trafficking of highly enriched uranium or plutonium.
The impact of a dirty bomb
Fortunately, the impact of a dirty bomb is still a matter for speculation and simulation, but the projected result of a detonating device in a crowded urban environment would be substantial and long-lasting.
The direct danger and damage arise from the detonation of the conventional explosives. Secondary damage is more significant in terms of economic disruption and health hazards. Rapidly developing panic would be likely, followed by mass self-evacuation of the population in a wide area surrounding the blast location. An increase in cancer incidence to inhabitants of the immediate area would be expected. Secondary economic disruption resulting from a long and complex decontamination process, loss of business, and loss in real estate value could range from billions to hundreds of billions. The decontamination process, if possible at all, would probably be long and expensive, much more than the six months it took to clean up Capitol Hill when some 5 grams of anthrax in five envelopes arrived on the Hill.
Mitigating dirty bombs: Current means and methods
In the words of Stephen Younger, director of the Defense Threat Reduction Agency, Washington: “There are various technologies for detecting nuclear materials. All of them could stand improvement.”
There are pager-size sensors that can detect weapons quantities of nuclear materials from a range of several yards. There are large, fixed and mobile “portals” capable of screening vehicles, containers and trucks, in some cases from a distance. All are effective in detecting unshielded materials. But if terrorists were to make a simple effort to disguise a device, enveloping it in a lead shield costing less than $100, detection by radiation detectors alone would be impossible.
To make things worse, nuclear medicine generates a high number of false alarms. According to Homeland Security Research Corp. (HSRC) analysis, in the United States alone, there are approximately 300,000 people who emit radioactive radiation after having undergone a recent nuclear medical procedure. Nuclear medicine patients and users of some other benign radioactive products could be a major source of false alarms.
Pagers — The U.S. customs equipped its inspectors with 5,000 pager-like radiation monitors. Although better than nothing, these pagers are usually a low-sensitivity item and can detect radiation only from a fairly short distance (several yards).
Radiation Detection Portals — The threat of nuclear devices and dirty bombs has prompted a current trend to install nuclear detection roadside portals. The purpose of these systems is to detect stolen and/or smuggled radioactive sources, weapons grade uranium and plutonium, as well as nuclear devices. All of these threats emit Gamma radiation; weapons grade plutonium and nuclear devices emit neutrons. These emissions were used for many years to detect theft and smuggling of radiological and nuclear materials from nuclear plants. To date, many hundreds of the very same devices are used to monitor vehicles in the former Soviet Union, to detect nuclear devices and mitigate smuggling of radioactive materials.
One paramount index of performance of nuclear threat detection roadside portals is their detection sensitivity to moving vehicles. All currently available threat detection devices were developed pre-Sept. 11; they are limited to slow-moving vehicles at speeds of 2-13 mph.
HSRC forecasts that most present nuclear-threat screening portals will become obsolete once a new generation is introduced, consisting of high-sensitivity (corresponding to high vehicle velocity) and high-resolution detectors (providing low false alarms) fused with “shielding” detection capabilities.
Nuclear Threat Screening Portal – Current Technologies — At the core of all nuclear radiation container/vehicle screening portals is a large-volume radiation detector that converts the Gamma or Neutron energy into electrical impulses representing the radiation flux intensity and energy. These electrical impulses are processed by analog and digital electronics that decide whether there is a surge of radiation above the natural radiation level.
There are currently three types of detectors:
Plastic scintillators: These are low-cost plastic materials that convert Gamma radiation into flashes of light (scintillations). The light flashes are picked up by high-sensitivity optical detectors (photo multipliers), and are converted into an analog electrical signal, which is further processed by an electronic system. The advantage of plastic scintillators is their low cost and the ability to construct large-volume detectors providing high sensitivity. The disadvantage of plastic scintillators is their inability to ascertain the energy of the Gamma radiation. The energy of the Gamma particles is the only means to identify the exact type of the Gamma radiation source. Moreover, plastic scintillators cannot detect neutrons.
Scintillation crystals: (e.g. NaI, CsI, BGO) are more expensive than plastic scintillators and less flexible in size and shape, but they provide good identification of the Gamma radiation energy, allowing the radiation source to be identified. This identification is an important tool in the reduction of false alarms. Scintillation crystals cannot detect neutrons. HSRC believes that the future belongs to cadmium telluride detectors — solid state detectors that provide excellent resolution and sensitivity.
Neutron detectors: The most common neutron detector used to date in radiological/nuclear screening portals is a container filled with He3. The He3 media converts the energy deposited by the neutron particles into a minute electrical signal. This signal is processed by an electronic system that determines the intensity of the neutron flux. A neutron detector cannot detect Gamma radiation.
The remedy — fused technologies
In view of the current shortcomings evident in radiation detection technologies, it is clear that a different approach is necessary. The techno-tactical assumption is that a dirty bomb will be carried either with or without a radiation-shielded package. The graph on page 36 depicts the cumulative installed base of luggage/baggage/cargo/container screening systems that will require either radiation detection upgrade or alternatively will be installed as fused dirty bomb screening systems.
HSRC forecasts that only fusing the technologies of high-sensitivity radiation detectors integrated with imaging technologies, such as mm wave imaging, will provide the optimal screening for dirty bombs. Such systems will be deployed in the future to screen people for most terror threats (see diagram on page 32).
ABOUT THE AUTHOR
Dan Inbar is the chairman and CTO of Homeland Security Research Corp. (HSRC), a San Jose, Calif.-based research organization dedicated to studying, analyzing and reporting about the Homeland security industry and products, and to providing the airport, seaport, enterprise and government security industry with market information, analysis and forecasts. Visit www.hsrc.biz