Newer Russian weapons, for example, are equipped with heat- and time-sensitive locking systems, known as permissive action links, that experts say would be extremely difficult to defeat without help from insiders.
"You'd have to run it through a specific sequence of events, including changes in temperature, pressure and environmental conditions before the weapon would allow itself to be armed, for the fuses to fall into place and then for it to allow itself to be fired," said Charles D. Ferguson, science and technology fellow at the Council on Foreign Relations. "You don't get it off the shelf, enter a code and have it go off."
About This Series|
The three articles beginning today are the culmination of a year-long effort to examine the challenges the United States faces more than three years after the attacks of Sept. 11, 2001. Previous articles have ranged from the threat posed by conventional truck bombs to the difficulty of tracking terrorist fundraising. The articles starting today take a detailed look at terrorists' ability to acquire and use weapons of mass destruction -- nuclear, biological and chemical.
While the dangers certainly are real, there is considerable disagreement among security experts about the probabilities for "catastrophic terrorism." In the case of nuclear and biological weapons, the subjects of articles today and tomorrow, there are technical and scientific hurdles that have proved daunting, even for nations with sizable budgets and state-of-the-art facilities. Chemical weapons, which will be explored in an article Friday, would be somewhat easier to devise or obtain, but also far less likely to yield huge numbers of casualties. A radiological device would have similar limitations for terrorists.
Each type of weapon presents special challenges for the groups seeking to acquire it, but experts warn that the odds for a successful attack could rise significantly in the future as determined foes intersect with advancing technology.
_____The World After 9/11_____
Attack With Dirty Bomb More Likely, Officials Say (The Washington Post, Dec 29, 2004)
U.S. Unprepared Despite Progress, Experts Say (The Washington Post, Nov 8, 2004)
Va.-Based, U.S.-Financed Arabic Channel Finds Its Voice (The Washington Post, Oct 15, 2004)
Moroccans Gain Prominence in Terror Groups (The Washington Post, Oct 14, 2004)
From a Virtual Shadow, Messages of Terror (The Washington Post, Oct 2, 2004)
Facing New Realities as Islamic Americans (The Washington Post, Sep 12, 2004)
In Search Of Friends Among The Foes (The Washington Post, Sep 11, 2004)
U.S. Eyes Money Trails of Saudi-Backed Charities (The Washington Post, Aug 19, 2004)
Impervious Shield Elusive Against Drive-By Terrorists (The Washington Post, Aug 8, 2004)
The strategy would require help from facility guards, employees with knowledge of the security and arming features of the weapons, not to mention access to a launching system.
Older Russian nuclear weapons have simpler protection mechanisms and could be easier to obtain on the black market. But nuclear experts said even the simplest device has some security features that would have to be defeated before it could be used.
"There is a whole generation of weapons designed for artillery shells, manufactured in the 1950s, that aren't going to have sophisticated locking devices," said Laura Holgate, who ran nonproliferation programs at the Pentagon and the Energy Department from 1995 to 2001. "But it is a tougher task to take a weapon created by a country, even the 1950s version, a tougher job for a group of even highly qualified Chechen terrorists to make it go boom."
Transporting a weapon out of Russia would provide another formidable obstacle for terrorists.
Most of the ready-made bombs that could be stolen would be those made with plutonium, which emits far higher levels of radiation and is therefore more easily detected by passive sensors at ports than is highly enriched uranium, or HEU.
"I wouldn't rule out plutonium altogether, but if one were a terrorist bent upon demonstrating a nuclear explosion, the HEU route is technically much easier," said William C. Potter, director of the Center for Nonproliferation Studies at the Monterey Institute of International Studies in California.
Building a Bomb
Such difficulties have led some nuclear experts to believe bin Laden would be more likely to try to build an improvised nuclear weapon using a combination of uranium and conventional explosives. That design, known as a gun-type device, was used in the atomic bomb over Hiroshima.
While the technology is relatively simple and has been described in dozens of published scientific studies and policy journals, the path to development is filled with technological and logistical challenges -- the most significant of which is obtaining at least 50 kilograms of bomb-grade uranium. That amount would yield a slightly smaller device than "Little Boy," the code name for the Hiroshima bomb, but would be enough to obliterate any life or structure within a half-mile radius of the blast zone.
"If they got less material than that, it would be really dicey that they could build such a bomb," said Ferguson, at the Council on Foreign Relations.
According to a database maintained by the United Nations' International Atomic Energy Agency, there have been 10 known incidents of HEU theft in the past 10 years, each involving a few grams or less. Added up, the stolen goods total less than eight kilograms and could not be easily combined because of varying levels of enrichment. Most important, the thieves -- none of whom was connected to al Qaeda -- had no buyers lined up, and nearly all were caught while trying to peddle their acquisitions.
"Making the connection between buyer and seller has proved to be one of the most substantial hurdles for terrorists," said Matthew Bunn, a senior researcher at Harvard University's Project on Managing the Atom. Of the few known attempts by al Qaeda to obtain HEU, each allegedly stumbled because there was either no seller or the material on offer was fake. "Each time they tried, they got scammed," said Bruce Hoffman, a counterterrorism expert at the Rand Corporation who has tracked al Qaeda for years.
A September report on terrorism by the Congressional Research Service warned that terrorists could "obtain HEU from the more than 130 research reactors worldwide that use HEU as fuel." The report noted that the nations of "greatest concern as potential sources of weapons or fissile material are widely thought to be Russia and Pakistan."