Luck plays a role in any technology project, but critics rarely give it due credit, preferring instead to blame failures on design. This tendency was on display last week, when pundits called North Korea's nuclear test a failure because it had the unusually low yield of about half a kiloton. Even the comedians got in their licks.
"The blast was so small that many scientists are saying it was a dud," said late-night television host Conan O'Brian. "Apparently, the nuclear bomb didn't work well because it was made in Korea."
No strategist ever went right by bad-mouthing an adversary, and so we welcome the corrective supplied by Richard L. Garwin, a distinguished physicist who helped design the first hydrogen bomb and has advised the U.S. government ever since. In a Q&A with Spectrum's William Sweet, Garwin agrees that the North Koreans must have wanted a bigger bang and thus may indeed have miscalculated. But he maintains that a chance occurrence could have caused a perfectly fine bomb to fizzle.
The chance occurrence, called predetonation, happens when stray neutrons trigger a tiny chain reaction before enough plutonium can be crammed into a small enough volume for a long enough time. Energy released in that reaction blows the plutonium apart before much of it has reacted.
Garwin points out that the possibility troubled the sleep of the original bomb-makers in Los Alamos, N.M., during World War II. "Oppenheimer said there was a 2 or 3 percent chance of a fizzle," he says, "and that there might be a substantial reduction in yield—but that it could never go lower than 5 or 10 percent of the expected yield." The North Koreans may thus have expected 5 to 10 kilotons. [The post originally said megatons, a rather large error, and we thank Dinesh Bansal for pointing it out to us in his comment, below.]
If so, then the designers may not need to make changes; they can just try again, and hope for better luck. "I'd expect another test within a few months that's likely to be a successful 4- or 5-kiloton device," Garwin says.
If current assessments of the North Korean plutonium stockpile are correct, such a "destructive test" would still leave enough material for another five bombs. That's one for each neighboring country and Uncle Sam besides.