WASHINGTON (AP) - President Barack Obama laid out a nightmare scenario on Tuesday - a terrorist with atomic bomb materials no bigger than an apple who could launch an attack killing hundreds of thousands of people.
In doing so, Obama skimped on details that make that kind of attack a more remote danger than he implied in his brief opening remarks to more than 40 world leaders, even as he got the broad picture right. The gathering, called by Obama, was intended to focus global attention on the problem of nuclear materials that could fall into the wrong hands.
Here's a look at the facts behind Obama's outline of the threat from nuclear terrorism:
OBAMA: Said in comparing today's threat to that during the Cold War: "The risk of a nuclear confrontation between nations has gone down, but the risk of nuclear attack has gone up."
THE FACTS: Yes, the bleak Cold War vision of mutual annihilation is all but gone now, and in its place is a new kind of risk. But linking the two, as he did, implies that the outcome from both scenarios is comparable.
He is correct that the numerical risk of an attack is higher now simply because there is so much material stockpiled and so many ways it could be misused. Yet the consequences are more limited now than from a nuclear exchange between superpowers with thousands of warheads each. The more likely scenario now is a limited attack confined to one city rather than global nuclear winter.
OBAMA: Said nuclear materials that could be stolen or sold for use as a weapon exist in dozens of nations.
THE FACTS: Correct. Arms control experts count roughly 40 nations with either weapons stocks or other nuclear facilities or material that could be misused. In most cases, however, the material or facilities are under what those nations claim is sufficient control.
OBAMA: "Just the smallest amount of plutonium - about the size of an apple - could kill and injure hundreds of thousands of innocent people."
THE FACTS: The apple might be a nice visual, but perhaps a little misleading.
Brookings Institution arms control expert Steven Pifer, largely agreeing with Obama, has one quibble: He says such a package would be closer to the size of a grapefruit.
More broadly, it is true that highly trained scientists and engineers with specialized equipment could fashion a small bomb that, as Obama said, could kill hundreds of thousands. But the facilities and technique needed to do so are presumed to be beyond the current reach of most terrorist groups or militant movements.
The scenario of a miniature but extraordinarily lethal bomb is hardly impossible, nonproliferation experts say, but probably represents less of a risk than a terrorist group getting hold of 50-80 pounds of enriched uranium and fashioning a crude device that would be larger and harder to conceal. Such a crude device might, however, be just as deadly.
OBAMA: "Terrorist networks such as al-Qaida have tried to acquire the material for a nuclear weapon, and if they ever succeeded, they would surely use it."
THE FACTS: Al-Qaida's desire for at least crude nuclear capability is taken as a given, although Obama and other U.S. officials have not spelled out exactly how the terrorist network has pursued atomic weapons so far.