EUROPEAN police have investigated hundreds of cases of alleged nuclear smuggling in recent years. Most were scams. A particularly common scheme involved petty crooks trying to hook big bucks for the specks of radioactive material found in smoke detectors.
Nothing confirmed by law enforcement agencies involved real weapons-usable material - until this summer. Now, last week's seizure in Munich of more than 12 ounces of stolen plutonium, with a case in May when German police found 2.5 ounces of incredibly pure plutonium, means the danger of nuclear crime has reached a troubling new level.
Fissile material found by police is ``beginning to bump up against the threshold of what it takes to make nuclear weapons,'' says Thomas Cochran, a nuclear arms expert at the Natural Resources Defense Council. ``It is less than an order of magnitude away.''
Much of the attention given the batches of fissile material seized in Germany in recent months has revolved around their places of origin. Western scientists have largely jumped to the conclusion that the plutonium involved must have come from Russian sources. Some Russian defense officials have heatedly denied the charge.
In some ways this argument is beside the point, say US experts. The nature of the plutonium indicates that it clearly did not come from Russian nuclear warheads and probably did not even originate from stocks intended for weapons use. But there are many other sources of nuclear material in the ex-Soviet Union that are not guarded as tightly as Russia's actual nuclear arsenal, including research labs.
Considering the state of Russia's society and the problems that even the United States has had keeping track of its own fissile material inventory, it is ``preposterous'' for Russia to say that its hundreds of tons of plutonium and highly enriched uranium are all accounted for, says Dr. William Potter, director of the Program for Nonproliferation Studies at the Monterey Institute of International Studies in California. A more useful dialogue would involve the West and the East ending mutual recrimination and working together to control a problem that poses a clear and common danger. ``There is a statistically high probability that there is material out there that has not been intercepted that may have been delivered to buyers,'' says Dr. Potter.
To understand why experts are so worried about the latest nuclear smuggling developments, it helps to understand a little about what kind of material bomb makers use.
Nuclear weapons can be made from two types of fissile material: plutonium and highly-enriched uranium. Though each has its advantages, plutonium is the preferred choice of sophisticated designs. It takes about 13 pounds of refined plutonium to make an explosive device, and about 100 pounds of enriched uranium.
All plutonium varieties, or isotopes, can be used to make explosive devices. The isotope plutonium-239 makes by far the biggest bang, and theoretically any terrorist looking for a nuclear weapon would want the highest percentage of PU 239 they could obtain. But other isotopes would still produce an explosion of tragic force - a yield of ``about one or two kilotons'' estimates David Albright, a nuclear program expert at the Institute for Science and Security.
In some ways plutonium with a low PU 239 percentage might even be preferable, says Albright, as it does not require some of the fancy initiation devices added onto US warheads.
Highly enriched uranium, on the other hand, needs to be isotope uranium-235 to be weapons-usable. Uranium below 6 or 7 percent U 235 won't work for bomb purposes, and an unsophisticated user would need something much more highly enriched than that.
The approximately 12-ounce plutonium sample seized from two Spaniards and a Columbian who flew to Germany from Moscow last week was 87 percent plutonium-239, according to German police. It was not in metallic form, as it would have been if it had come straight from a warhead. It was reportedly a powder, indicating that it was perhaps from a plutonium reprocessing facility. It might have been intended for use as fuel in nuclear reactors, some of which are set up to burn a plutonium uranium-oxide mix.
Perhaps even more frightening was the 2.5-ounce sample seized from a suspect named Adolf Jaekle by German police in May, and confirmed publicly by investigators only recently. That sample turned out to be 99.7 percent plutonium-239 - a purity unusual even by US weapons standards.
This purity, combined with some other trace elements, led Western scientists to conclude that the sample must have been enriched in a particular process found only at one Russian lab. This distinctive fingerprint was unusual, however. While scientists might have some idea where the larger sample seized last week came from, ``you can't really determine where it's from without Russia's cooperation,'' says David Albright.