Could a Free-Lancer Build a Bomb?

By MICHAEL D. LEMONICK

First you have to get the plutonium or the uranium. Either material will do the job. But since much of the nuclear stuff offered for sale is bogus, a smart buyer would need access to a no-questions-asked research lab, perhaps in a place like Iran, to test the material. An amateur would use about 18 lbs. of 94% plutonium-239 or 55 lbs. of uranium to make a Hiroshima-strength bomb. Then you have to detonate it. The basic principles of bomb technology are available to anyone who knows where to look up the information, but actually constructing one is not quite that simple.

A handful of conspirators in a garage, like the World Trade Center bombers, would almost certainly lack the money, technical know-how or laboratory equipment to fashion nuclear raw materials into a working weapon. In fact, experts believe that it would be extremely difficult for most terrorist groups to make an atom bomb without the resources of a friendly country. The task, says Spurgeon Keeny, a physicist who is executive director of the Arms Control Association in Washington, is like building an automobile. Many people know how one is assembled, "but there is a lot of difference between that and sitting down in your shop and doing it."

Plutonium is generally more available than enriched uranium but harder to build a bomb with. Smuggling enough stolen plutonium is reasonably easy: the gray metal commonly comes in 2-lb. bars or gravel-like pellets. While it is highly toxic to breathe in -- one grain can cause lung cancer -- its radioactive alpha rays do not penetrate very far, so thick lead shields are not necessary. But airport metal detectors, which would register any sizable quantity, are to be avoided.

While the U.S. or Russia could make a miniaturized bomb with as little as 6 lbs. of bomb-grade plutonium-239, a beginner could hope to produce only a much larger, cruder device from his 18 lbs. The fissionable metal for a bomb core has to be melted down and fashioned into a virtually perfect sphere about the size of a tennis ball -- called a pit -- a tricky process that takes a well- equipped nuclear laboratory. To make the bomb reach critical mass and set off a chain reaction -- nuclear fission -- you have to make the sphere implode in on itself. That requires a bang from about 800 lbs. of conventional explosives, packed around the plutonium. But the implosion has to apply perfectly uniform pressure from all sides, so all the explosives have to go off at exactly the same time, triggered by precisely placed high-energy capacitors -- devices capable of releasing enormous, rapid bursts of electricity. The right timing devices require a level of technology available only to highly trained engineers working in well-equipped labs. Much of the lab work can be bypassed by purchasing ready-made plutonium pits extracted from dismantled nuclear missiles. These spheres have already been machined and need only the surrounding detonation gear to set them off. Yet so far, Russia has apparently kept close tabs on its sizable stockpile.

An alternative fuel is enriched uranium, which is uranium purified to boost the percentage of the rare isotope U-235, but you would need at least 55 lbs. The material is harder to come by than plutonium because it is usually stored in well-guarded military facilities, but it is easier to turn into a crude bomb. Making it explode is a relatively simple matter of firing one chunk of uranium, like a bullet, into another, larger chunk. The pieces have to be shaped properly, but the tooling necessary is nowhere near as precise as that needed for a plutonium bomb.

This kind of bomb, which terrorists could conceivably make, would deliver at most one-tenth the energy of the Hiroshima and Nagasaki devices -- but that is still equivalent to 1,500 tons of TNT. While such a device would weigh a few thousand pounds, it could be transported in a small truck or a large van. A bomber could simply drive it into an underground garage, like the one at the World Trade Center, park it and get as far away as possible before detonating it by remote control. The nuclear explosion could bring down one of the towers and kill virtually everyone inside the complex. Eventually, the bomb would cause at least 100,000 deaths from the blast and radiation.

With reporting by Janet I-Chin Tu/Washington