A nuclear attack is by far the most challenging technological feat for terrorists. Yet Graham Allison, assistant secretary of defense in the first Clinton administration and now director of the Belfer Center for Science and International Affairs at Harvard University, places the odds of a nuclear strike within the next decade at 51–49—slightly worse than the toss of a coin. "A nuclear terrorism attack is inevitable if we continue on the autopilot path we're on," he says.
And what would such an attack do? Allison has posted the grim answer on his Web site (www.nuclearterror.org), which shows a three-color "blast map" depicting the effects of a 10-kiloton bomb, about the smallest a workable nuclear device could be. In the red zone, within one-third of a mile of Ground Zero, the bomb would destroy buildings, people, and just about anything else; in the green zone, within three-fourths of a mile, people would either die immediately or be seriously injured by fire and radiation. For a plausible target like Lower Manhattan, that could easily translate to tens of thousands of fatalities.
Allison has some good news as well. The image of a clandestine terror group buying an old Soviet nuke on the black market is almost certainly a Hollywood fantasy. Despite the chaos following the breakup of the Soviet Union—which left 18,000 nuclear warheads in the hands of new and mostly poor nations—there is no evidence that any of our old adversary's tactical or strategic nuclear weapons ever left government control. Allison credits the furious work by the American and former Soviet governments, done partly under his watch: "Had nothing been done, there would already have been a nuclear attack."
It is now highly unlikely that any rogue group could get its hands on an existing nuclear weapon, because the devices are well-guarded and have fail-safe protective mechanisms that no amateur is likely to crack. Russian officials admit that terrorist teams managed to carry out reconnaissance on two nuclear warhead storage facilities and two nuclear-weapon transport trains in 2001 and 2002, but the teams never came close to being able to steal them, much less figure out how to use them.
Building a nuclear bomb from scratch would be a huge undertaking for any terrorist cell, which is why some other security analysts see less nightmarish odds than Allison does. A group of international security experts polled by Senator Richard Lugar puts the average probability of a nuclear attack on U.S. soil within a decade at around 29 percent, still plenty terrifying. Mathew Bunn, one of Allison's colleagues at Belfer, places the risk at more like 5 to 10 percent—high enough to make it the top national-security concern.
The problem is that the nuclear cat is out of the bag. These days, finding bomb-building instructions is almost comically easy. Two declassified U.S. government publications, based on the work of Manhattan Project scientists, offer detailed guidance. Both are available on Amazon.com for a total of $40.76, plus shipping. And there is little question that Al Qaeda is interested in going nuclear. Former CIA analyst Michael Scheuer reports that in 1996 the "CIA's Bin Laden unit acquired detailed information about the careful, professional manner in which al-Qaeda was seeking to acquire nuclear weapons." In 2003 Bin Laden made the dramatic gesture of requesting a fatwa from a radical Saudi cleric authorizing the use of a nuclear bomb against American civilians (not surprisingly, it was granted).
Transforming those dark desires into reality would require a minimum of 50 pounds of highly enriched uranium, about 1,500 carefully machined parts, a nuclear design engineer, and more than a dozen craftsmen able and willing to put the device together. A. Q. Kahn—the so-called father of the Pakistani atomic bomb program—may have sold portions of that nation's nuclear technology to Libya and perhaps to terror groups as well, according to an Institute for Science and International Security report. As for fissile material, Russia is deemed a major nuclear-supply risk because it has large amounts of enriched uranium stashed away. Security of nuclear materials worldwide "ranges from 'better than probably necessary' to 'absolutely appallingly bad,'" Bunn says.
The situation there is improving, in part because of the Nunn-Lugar Cooperative Threat Reduction Initiative, a program that aims to decrease the risk of nuclear or radiological attack by, for example, locking down nuclear material from the former Soviet Union. The Megatons to Megawatts program has secured 269 metric tons of highly enriched uranium and turned it into reactor fuel. On the other hand, the stuff keeps turning up in unexpected places, such as Uzbekistan, where the International Atomic Energy Agency recently recovered three bombs' worth of highly enriched uranium. "What the heck are three bombs' worth doing in Uzbekistan?" asks Allison. He notes that recent reports indicate several other countries—including Ghana, Belarus, and South Africa—also have nuclear material they shouldn't.
Former prosecutor Andrew McCarthy thinks Allison may be focusing on the wrong nuclear fear. Triggering nationwide panic wouldn't require a nuclear explosion. A dirty bomb—radioactive material by a conventional explosive—"is much less of a problem to detonate and if successful would render a large swath of a big city uninhabitable for years," he says. Raw materials are far easier to obtain. Dirty bombs don't need exotic enriched uranium; any highly radioactive material will suffice. Millions of such sources are scattered around the world, including hospitals that use radioactive isotopes in the treatment of cancer and in the radioisotope thermoelectric generators, or RTGs, that power remote Soviet installations with the heat produced by nuclear decay.
The impact of a dirty bomb would be far less than that of a true nuclear device, and the radiation would probably not harm many people. "It is likely that very few Americans will be killed directly, suffer radiation sickness, or even have a measurably increased risk for cancer from an attack," Peter D. Zimmerman and Cheryl Loeb write in "Dirty Bombs: The Threat Revisited," a report published by the Center for Technology and National Security Policy, National Defense University. The primary threat of a dirty bomb would be the economic fallout. Cleaning up the radiation would entail ripping down all contaminated structures and sending them to a special dump. A dirty-bomb attack on a major American city could easily cost more than the $30 billion of the 9/11 attacks, Zimmerman and Loeb say.
One solution is to develop better tools for cleaning up a deliberate radiation release. Researchers at Los Alamos National Laboratory are working on foam that would bind to radium, cesium, and strontium, likely components of a dirty bomb. When peeled off buildings, the foam would take most of the radiation with it.
A much better way to prevent a nuclear or dirty-bomb terrorist attack is to keep radioactive ingredients from getting inside the nation's borders in the first place, and here physics is on our side. Radioactive materials, by their very nature, emit gamma rays or other distinctive radiation signatures.
After 9/11, U.S. Customs and Border Protection launched what it calls the Container Security Initiative to search for nuclear materials and other terrorist threats before they enter the United States. The initiative now scans for gamma rays and neutrons and performs X-rays of the contents of high-risk cargo in 44 foreign ports, which collectively handle 77 percent of the containers entering the United States. Because of the limited capacity of current scanners, however, only 17.5 percent of that high-risk cargo actually got scrutinized. In April 2005, the Department of Homeland Security founded the Domestic Nuclear Detection Office to add a second layer of security, this time on American soil. That new office recently deployed 214 radiation monitors that scan for gamma rays and neutrons at the "choke point," where the containers pass out of the port. More than 600 are scheduled for deployment by late 2007.
Current scanning systems generate a lot of false alarms that require investigation, drastically slowing the screening process. They can also be fooled by radiation-absorbent materials, like lead, that soak up low-energy gamma rays. Dennis Slaughter, a nuclear physicist at Lawrence Livermore National Laboratory in Livermore, California, is therefore developing a smarter scanner that seeks radioactive material actively, not passively. His device—which his team somewhat ominously calls a nuclear car wash—fires a beam of neutrons into the item to be scanned. If the neutrons hit uranium or any other fissionable nuclear material, they will release gamma rays energetic enough to penetrate most types of shielding. These high-energy rays are also easily distinguished from normal background radiation, cutting down on false positives. Livermore is partnering with General Electric to build a production version.
At Brookhaven National Laboratory on Long Island, nuclear physicist Peter Vanier and his colleagues have created a complementary device tuned to pick out smuggled plutonium, another key material for nuclear weapons. Not only can it detect hidden nuclear material, it can also take a rough image of it. The Brookhaven scanner, in essence, functions like a pinhole camera for nuclear snapshots and looks like one, too—little more than a decorated box. Its "lens" is a series of rectangular holes that project incoming neutrons onto two gold-plated tungsten wires, each just 12 microns [1/2,000 inch] thick, in the back of the camera. The scanner also incorporates a circuit board lined with copper strips and enclosed in a chamber pressurized with helium-3, a rare isotope that reacts with neutrons.
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| Neutron detectors being designed at Brookhaven National Laboratory can image radioactive materials found in cargo containers from hundreds of feet away. |
When American security forces intercept nuclear material being smuggled into the country, another technology comes into play: nuclear forensics. Each nuclear sample has a host of distinctive attributes, including the exact mix of impurities, the ratio of different radioactive isotopes, even embedded carbon compounds that indicate the sample's age. Using these kinds of clues, German police in 1996 traced a cache of mysterious nuclear pellets to one of just two nuclear manufacturing plants, one in Russia and the other in Kazakhstan. Russian officials now keep a database of forensic characteristics of all major nuclear stockpiles in the country to better track down any material if ever stolen.
Allison summarizes the problem as "follow the golf clubs or follow the drugs." An American who buys golf clubs abroad and doesn't want to declare them can send them via a company that packs them in a shipping container, which then slips them into port without ever being seen by customs agents; the ability of drug dealers to bypass even the most elaborate border controls is a well-known problem. We are engaged in a high-stakes game of hide-and-seek, Allison says, "and it is inherently easier for hiders than seekers."
