Joe Cirincione writes for Foreign Policy:
If I were Iran, if I were Iran -- a crazed fanatic, I'd say let's get a little fissile material to Hezbollah, have them carry it to Chicago or some other place, and then if anything goes wrong, or America starts acting up, we'll just say, "Guess what? Unless you stand down, why, we're going to let off a dirty bomb." I mean this is where we have -- where America could be held up and blackmailed by Iran, by the mullahs, by crazy people. So we really don't have any option but to keep Iran from having a nuclear weapon.
--- Mitt Romney, May 17, 2012
Governor Mitt Romney's description, caught on video, of what he considered the real nuclear threat from Iran has further undermined his national security credentials, showing a fundamental misunderstanding of nuclear threats. Iran's nuclear program has nothing to do with dirty bombs. Terrorists would not use uranium -- from Iran or anywhere else -- in a dirty bomb. It is unclear if Gov. Romney was just riffing, or if his advisors had fed him this line of attack. But it is dead wrong.
Nuclear bombs are serious business, and preventing their spread and their use against the United States is perhaps the paramount duty of the president, who, of course, is also responsible for any decision to use America's own arsenal. The main reason we are so concerned about Iran is that its uranium-enrichment facilities could produce the fissile material needed to make a nuclear bomb. Anyone running for the highest office in the land simply must know the basics about dirty bombs, nuclear weapons, and the threat from Iran. This video does not help Gov. Romney prove that he does.
A dirty bomb is basically a truck bomb laced with radioactive materials. Such a device (also known as a radiological weapon) uses conventional explosives like dynamite or C-4 to spew radioactive materials over large areas. The explosion would be relatively small, but victims would be exposed to life-threatening levels of radiation. The radiation would prevent emergency response teams from reaching the victims quickly and could contaminate large areas for years, requiring expensive cleanup.
A terrorist could also do a reverse dirty bomb: bring explosives to a source of radioactive material such as a nuclear reactor, a spent-fuel pool, or a factory making radioactive isotopes.
Dirty bombs (which have never been used) are very different from nuclear bombs, which trigger a chain reaction in a small core of fissile material -- highly-enriched uranium or plutonium -- to produce a massive explosion. The explosion produces heat, blast, and radiation that all cause catastrophic damage.
The key here is that dirty bombs do not use fissile material. They do not use enriched uranium or plutonium -- the fissile material that Gov. Romney cites. The reason is simple: These materials, perhaps counterintuitively, are not radioactive enough. Their radioactive emissions don't travel far and are blocked by simple barriers, including skin and clothing. A dirty bomb would use small amounts of highly radioactive materials such as cesium or cobalt, not uranium. Even specks of these elements send out deadly gamma rays that penetrate walls and bodies causing immediate injury.
The Federation of American Scientists has calculated that a mere 41 grams (1.4 ounces) of cesium-137 in a dirty bomb could contaminate most of Manhattan. By contrast, it would take 1,460 tons of low-enriched uranium to get the same levels of radiation. That pretty much tells you all you need to know. Iran does not have any plutonium, so getting "a little fissile material to Hezbollah" would mean shipping them some 1,400 tons of uranium -- when all Iran has now is 6 tons total.
Iran's production of enriched uranium has nothing to do with dirty bombs. The core problem is that Iran is enriching uranium it says is for reactor fuel but could be turned into fuel for nuclear weapons. The most important reason to contain Iran's nuclear program is to prevent a dangerous, destabilizing nuclear arms race in the Middle East and an emboldened Iranian regime -- not to prevent Iran from giving terrorists nuclear materials for a dirty bomb. And it is crucial that anyone involved in the discussion of Iran's nuclear program -- and certainly the Republican presidential nominee -- understand this.