Experts say the international community must continue efforts to ensure that nuclear weapons don't fall into the wrong hands.
"Loose nukes" is a colloquial term referring to nuclear bomb material -- or actual nuclear weapons -- that are not adequately secured or accounted for. Experts say the danger is that these materials could be stolen or sold to a criminal or terrorist organization that would then manufacture a crude nuclear weapon.
Matthew Bunn, a nuclear threat and terrorism expert at Harvard University's Belfer Center, says there are four major factors in assessing how urgent the nuclear threat is in a particular country or at a particular facility.
"First, the quantity of material -- that is, is there enough material there to make a nuclear bomb or is it much less than what you need for a bomb? Second, the quality of the material -- would it be very difficult to process to make it into a bomb? Third, the security level at the facility; and fourth, the level of threat at the facility," says Bunn.
Russian Weapons Control
Based on those criteria, Bunn and other experts -- such as Daryl Kimball, head of the Arms Control Association -- say the greatest concern for the last 15 years has been Russia.
"During the communist era, Russia had a relatively good security system enforced by the K.G.B. [secret police] to make sure that Russia's rather extensive network of research facilities and military facilities with these materials and weapons were secure. But with the collapse of the Soviet Union and the breakup, the ability of the Russian government -- and especially the governments in some of the other former Soviet states -- to secure these materials has degraded," says Kimball.
But experts say since the fall of the Soviet Union [in 1991], the United States has been helping Russia to secure so-called "loose nukes."
David Mosher, a nuclear weapons expert with the RAND Corporation, says "The United States has spent a lot of money working with the Russians to try to get materials and weapons locked up or consolidated in fewer places. At the end of the Cold War, they were spread out over Russia in a lot of different places. And there has been some consolidation that has gone on -- helping the Russians dismantle old weapons, so that weapons that are no longer being used have been taken apart. And some of the fissile material from those weapons has actually been bought by the United States to turn to fuel for nuclear reactors."
Nuclear Threats and Islamic Radicals
Mosher says the problem with Russian "loose nukes" has not been nearly as bad as previously thought. But he says one country that must tightly secure its nuclear arsenal is Pakistan.
Daryl Kimball from the Arms Control Association says the United States and Pakistan are addressing the issue of nuclear security. "The United States government has very quietly, behind the scenes, been discussing with the government of Pervez Musharraf certain strategies to better secure Pakistan's [nuclear] facilities. But what the United States government has done and how much Pakistan has cooperated is not known outside of very small government circles."
Kimball says there is another dimension to the nuclear issue, not tied to weapons. "We also need to be thinking about the dozens of other countries around the world that possess reactors that use highly enriched uranium as fuel. There are research reactors, generally smaller reactors, in dozens of countries that were built with the assistance decades ago of the United States or the Soviet Union, that still contain highly enriched uranium which is usable in nuclear weapons," says Kimball.
Nukes for Sale?
Analysts say a major concern is that someone working either at a nuclear weapons facility or civilian reactor might sell nuclear materials to a terrorist group.
But Matthew Bunn from Harvard University says that hasn't happened yet. "We are not aware of any cases so far where highly enriched uranium or plutonium, which are the essential ingredients of nuclear weapons, have in fact been transferred to terrorists," says Bunn. "That doesn't mean it hasn't happened, it just means that we don't have any evidence that it has. And there does not appear to be a sort of organized, consistent market for this kind of material in the way that there is for illegal drugs or something like that."
Analysts say it would take several kilograms of plutonium or about 20 kilograms of highly enriched uranium to make a nuclear bomb. So far, the documented cases of people trying to sell those substances illegally involved just several grams.
In addition, Kimball says it would be difficult for a terrorist group to obtain nuclear materials. "It would require an extremely sophisticated, well-financed organization to acquire substantial quantities of plutonium or highly enriched uranium to make a bomb. Then you also have to consider that that organization would have to have the expertise or hire the expertise to manufacture a crude nuclear weapon."
Kimball and others believe the best way to ensure that "loose nukes" do not fall into the wrong hands is for governments to devote far greater resources and cooperate closely in establishing ever more stringent security measures around facilities housing nuclear materials.
This story was first broadcast on the English news program,VOA News Now. For other Focus reports click here.