A radioactive “dirty bomb” is a terrorist’s dream weapon–one designed to maximize panic and disruption to daily life, even if there are few immediate casualties.
By coupling common explosives such as dynamite with radioactive materials, terrorists could produce a plume of radioactivity that would contaminate people and buildings, potentially crippling a local economy and spreading fear nationwide.
But it is a far cry from a nuclear bomb. In fact, many experts believe the the shrapnel produced in the explosion would be far more deadly than the radioactive material it spreads, including cancer deaths years in the future.
Before the disclosure Monday that a man linked to Al Qaeda allegedly plotted to build a dirty bomb, local and federal government agencies were anticipating the possibility of such an event and are coordinating emergency response efforts for the Chicago area from Milwaukee to Gary.
A dirty bomb would be relatively easy to make, experts say. Radioactive material from any source is wrapped with conventional explosives such as dynamite or even fertilizer, as was used in the Oklahoma City bombing. When the bomb explodes, it turns the radioactive material into dust particles that can spread in a cloud or by winds.
“The hazard depends on the size of explosive that’s used and the amount and type of the radioactive material,” said Dan Smith, chief of research of the Center for Defense Information in Washington.
“The immediate radius of the explosion would kill people. If there’s a gamma ray source [among the most penetrating forms of radiation], some people would be exposed to intense radiation.
In a wider area, you might have some radiation sickness and the possibility of long-term cancers developing.
“But this would be nothing, compared to a nuclear detonation.”
The Nuclear Regulatory Commission has registered more than 2 million radioactive devices, tools or materials used for purposes ranging from cancer treatments to scanning metal for cracks.
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Each year the NRC reports hundreds of these items lost or stolen. In a dramatic case, two spent nuclear fuel rods have been unaccounted for since the 1980s, although many believe they were improperly sent to a low-level nuclear waste dump, not stolen.
Radiation threat
The radiation threat from a dirty bomb depends on the type of material used. The more radioactive the material, the more intense the doses of radiation, which are commonly measured in millirems.
For example, a cobalt-60 rod used for food irradiation could deliver an average dose of a few hundred millirems to people within a half mile, said Andrew Karam, radiation safety officer at the University of Rochester in New York.
This compares with the 300 to 400 millirems people receive annually from natural sources and 500 millirems, the typical annual limit for nuclear radiation workers, most of whom receive less than 100 millirems of exposure annually.
Argonne National Laboratory, a national center for developing a response to a dirty bomb, has trucks and other equipment specially outfitted to respond to a radiological attack.
“There is a growing cooperation by emergency response agencies throughout this immense metropolitan center,” said physicist Harvey Drucker, associate director of Argonne and director of the laboratory’s research and development effort for national security.
“The emergency forces know what tools they can get and where to get them. It’s all starting to come together. It’s getting set up and heading in the right direction.”
In the event of a dirty bomb explosion in the U.S., people should stay indoors and follow emergency instructions broadcast on TV and radio, said Dr. David Grdina, professor of radiation and cellular oncology at the University of Chicago.
The only authoritative data for calculating radiation-based cancer risks comes from survivors of the atomic bombs dropped by the U.S. on Hiroshima and Nagasaki during World War II.
But scientists warn against extrapolating cancer risks from those doses–hundreds to thousands of millirems compared with a few hundred millirems from a dirty bomb.
“A dirty bomb would probably not lead to many, if any, cancer deaths,” said Karam, speaking for the American Institute of Physics.
He added that radiation exposure from a dirty bomb probably would be less than what international scientific organizations typically warn against.
One scenario
The Center for Strategic and International Studies, a think tank, studied possible effects of a dirty bomb on Washington for city and federal officials this spring.
In its simulation, it found that public officials were ill-prepared to deal with the panic that likely would follow the attack.
Phil Anderson, a former Marine colonel who works for the think tank, said the group went into the study thinking that the detonation of a dirty bomb was a “remote possibility. We ended up knowing that it is a real possibility.”
He said terrorists are more likely to use cesium-137, which is available from medical sources, than plutonium or uranium, which are deadlier radioactive isotopes but harder to obtain.
In the group’s simulation, a school bus loaded with TNT and cesium-137 was parked in front of the Smithsonian Institution’s National Air and Space Museum, a popular tourist attraction on the Mall. The explosion destroyed the building and killed thousands of people inside.
But the destruction caused by the conventional explosion was limited to a four-block area. The radiation released by the bomb spread over 25 percent of Washington in a plume driven by a stiff wind.
Anderson said the radioactive contamination from this simulated bomb would have long-term health effects but would not kill many people. The incidence of cancers and cataracts would rise. The more profound effect would be on the psyche of citizens, he said.
“FDR said the only thing we have to fear is fear itself,” Anderson said. “It’s the fear we have to be worry about.” Large portions of the population are not in grave danger, he said. Such a bomb “will kill people, but it’s going to be isolated.”