Size Doesn’t Matter. The Test Does

Kim Jong Il's big bang may not have been so big after all. North Korea's nuclear detonation sent enormous diplomatic shock waves through international capitals, to be sure, and governments are still scrambling to respond. But technical experts from Beijing to the Beltway observe that it was small by traditional standards and could have been a failure, or at least less than an unalloyed success. The explosive yield of Pyongyang's test apparently was little more than half a kiloton, just a fraction of the explosive yield range that wanna-be nuclear powers historically have aspired to. No first-time test by any of the seven previous declared nuclear powers is thought to have been less than nine kilotons.

North Korean authorities expected to conduct a nuclear test in the four-kiloton range, and told Chinese counterparts so in a 20-minute warning before the imminent detonation, according to Washington reports quoting an unnamed U.S. official. But American experts say what actually took place was a "sub-kiloton explosion." Although Beijing officials declined to confirm or deny that report, a Chinese source close to the government—who requested anonymity because he was not cleared to talk to the media—suggested to NEWSWEEK that the blast conducted by the Democratic People's Republic of Korea (DPRK) was less than a complete triumph. "DPRK authorities said it was successful, but then why haven't they declared their data? The yield in kilotons has been announced by Japan, South Korea and Australia," said the source, "But not by Pyongyang. This makes people suspect [that] it wasn't a total success."

If the first explosion went partly awry, or was intentionally small, experts say it might be followed by an additional test or tests designed to generate more extensive data.  As a precedent, on May 11, 1998, India first announced the detonation of three underground nuclear explosions and then the following day conducted two more tests for which the explosive yield was very low, in the range of .2 to .6 kilotons. India insisted the last two were higher-yield than reported, while some Western experts interpreted them to be fizzles instead.

How much does size matter? American, South Korean and French scientists placed the yield of Pyongyang's blast at around 0.55 kilotons, possibly less. (The Russian defense minister's declaration that North Korea had successfully detonated a nuclear blast equivalent to between five and 15 kilotons of TNT has largely been dismissed.) If the low Western estimates are accurate, that means the yield of North Korea's explosion was much weaker than the 22-kiloton bomb that the United States dropped on Nagasaki, Japan, in 1945.

Western experts point to a number of possible explanations for Pyongyang's low explosive yield. It could mean that only a portion of the device's core exploded. Or that a modest amount of plutonium was used, possibly because North Korea wanted to conserve its supplies. A third possibility is that North Korean scientists had intended to test the device's design rather than its yield. Or, fourth, that they'd succeeded in manufacturing a small, more sophisticated nuclear device—a possibility seen as alarming but less likely.

Kim Taewoo, a senior research fellow at the Korea Institute for Defense Analysis and one of South Korea's top nuclear policy specialists, rules out another line of speculation currently making the rounds: that the blast was actually due to conventional explosives. Instead, he believes North Korea possesses at least five nuclear "bombs"—by which he means weapons, not simply devices—but that it probably tested an n-device built specifically to display a capability, in order not to waste one of his precious weapons.

Even if it wasn't a total success, North Korea's blast has to be taken seriously. Bigger isn't always better. A-bombs that implode a ball of plutonium are easiest to create in the 12- to 18- kiloton range. Bombs smaller than that require greater sophistication and more precise designs. Smaller is actually scarier, says Kim. "Some will say [North Korea's test] was a small blast and therefore a failure. But small may be more deadly because if the North has mastered doing small blasts it means they can make small bombs—and terrorist groups prefer small bombs. In the world of global terror, it's the small bombs that we should be worried about."

Indeed, Washington's biggest worry is not that North Korea is poised to launch a nuclear attack, but rather Pyongyang's habit of sharing its weaponry with regimes unfriendly to the United States, says Robert Einhorn, former assistant secretary of State for nonproliferation. Despite Pyongyang's reported threat Tuesday to "fire a nuclear missile" at the United States if Washington doesn't move to resolve the current crisis, North Korea is not believed to possess the accurate long-range missiles required to hit U.S. territory, even in the Pacific. In July, North Korea's test launch of a long-range Taepodong missile which could theoretically reach Alaska or Hawaii failed after 40 seconds.

Ever since the birth of the atomic bomb, scrutinizing each new test for clues about the ambitions and arsenal of the government that just went nuclear have been part of the international fallout. In 1950 the first American officer of the newly formed CIA to be killed in the line of duty was Douglas Mackiernan, an "atomic spy" in China's remote western region who, among other things, had been in Central Asia to monitor the first Soviet nuclear test. (Because he had worked under diplomatic cover, he was named at the State Department as a U.S. diplomat who died in the line of duty, but at CIA headquarters Mackiernan's death is marked by an anonymous star on the Wall of Honor.)

Getting and analyzing test data isn't always easy. Seismic waves triggered by Monday's detonations were detected by sensors across the globe. (In contrast to natural earthquakes, explosions usually have a telltale wave pattern, with a strong initial spike and up-and-down "Raleigh waves" signifying a shallow event). But the precise yield, or force, is difficult to determine without specific knowledge of the geological composition and mineshaft structure at the test location, since these factors affect the size of the shockwave, and hence any estimate of yield, according to Kim Taewoo. A more precise assessment of Pyongyang's blast could take days, awaiting input from airborne monitoring devices—including "sniffer" systems which analyze particles and gases in the atmosphere.

Just because a sub-kiloton blast may suggest a partial test failure doesn't mean small, crude bombs can't inflict great damage. Even without a long-range delivery system, a modest nuclear bomb could be transported by conventional means to any of North Korea's frontiers. Consider this disturbing scenario: the North Korean dictator tries to blackmail the world's wealthiest nations, threatening to detonate a two-kiloton atomic bomb hidden inside a shipping container somewhere in the teeming port city of Hong Kong ... He declares that any attempt to disarm the device would result in "a nuclear holocaust for Hong Kong and the crippling of the world trading system."

Simulations of this scenario, using Pentagon-designed software, were conducted by Matthew McKinzie of the Natural Resources Defense Council. The calculation was that a two-kiloton bomb detonated on the ground in Hong Kong (pop. 7 million) would kill some 87,000 people and destroy more property than the far bigger bomb that devastated Nagasaki at the end of World War II and killed an estimated 70,000 civilians. Now, just substitute for Kim a nonstate rogue player such as Al Qaeda, and that's when the scenario gets really believable—and scarier still.