What's in a Yield?

After careful analysis, the U.S. intelligence community has confirmed that North Korea did, indeed, test a nuclear device last week. Conclusive evidence came in the form of air samples, collected by our intelligence platforms after the test. Those samples contained traces of at least two radioactive gases associated with nuclear blasts. It would be virtually impossible for Pyongyang to "fake" that sort of evidence, indicating that North Korea did conduct a nuclear test.

And, if that weren't enough, there are signs that Kim Jong-il may be preparing for a second test. Both ABC News and NBC News reported Monday that suspicious vehicle activity and personnel movements had been observed near the site where the first test was conducted. The activity may represent the early stages of preparations for a second nuclear blast, although the preparations detected are far from conclusive. However, activity observed with the initial test provides a baseline for future events, providing analysts with tip-offs that be a predictor of additional tests.

But the real story from last week's test is the surprisingly low yield from the blast. According to U.S. estimates, the device detonated by the DPRK had an explosive force equal to 1,000 tons of TNT, or roughly one kiloton. By comparison, the atomic bomb dropped on Hiroshima in 1945 had a yield of six kilotons; nuclear devices detonated by India and Pakistan in 1999 (a more useful yardstick) were in the 6-13 kiloton range, with the Indian weapon toward the higher end of that scale, and the Pakistani device toward the lower end.

The comparison to India and Pakistan is important, since North Korea (allegedly) had access to Pakistani bomb designs, thanks to the A.Q. Kahn proliferation network. A North Korean device based on proven Pakistani designs should have produced a bigger blast--at least in theory. Credible reports from the late 90s suggest that the Pakistani bomb detonated after the Indian test was only partially successful. If the North Korean weapon shared critical design features with its Pakistani counterpart, it may have inherited some of the problems associated with early devices built by Islamabad, and resulting in a smaller blast, like the one detected last week At this point, Pyongyang might be described as "barely" a member of the nuclear club, with significant hurdles that must be overcome before North Korea can produce smaller, higher-yield weapons, cable of fitting atop a ballistic missile.

Of course, there are other explanations for the small bang detected last week. Richard Miniter, a respected writer on security matters, believes the low-yield explosion is proof that Pyongyang may have perfected a "suitcase" nuke, an ideal weapon for client states (and terrorist supporters) in Syria and Iran. Miniter's theory is within the realm of possibilities, but I'm not quite prepared to climb out on that limb, for a couple of reasons.

For starters, a nation's first nuclear device tends to be a bit larger than follow-on versions. Downsizing a nuke to fit atop a missile remains a complex proposition, despite the availability of outside help, and 60 years of accumulated nuclear know-how, much of it readily available in scientific papers and on the internet. Prototype nuclear devices-like the one detonated in North Korea last week--tend to be larger weapons, best encapsulated in an oversized gravity bomb. While the DPRK clearly wants smaller warheads for its ballistic missile force, it likely lacks the technology to produce those weapons, at least for now.

In fact, there is general consensus in the U.S. intelligence community have long viewed the "size" issue as a major limitation of North Korea's current nuclear program. However, this obstacle will be eventually overcome, if history is any indicator. For virtually every member of the nuclear club, smaller weapons typically come a bit later in the development process, after the nuclear technology has been perfected. For example, U.S. tactical nuclear weapons in today's arsenal are much smaller than the Hiroshima or Nagasaki bombs, but deliver a yield that is many times more powerful. Working with much more limited resources, it will take Pyongyang a while to develop smaller, more tactically viable weapons. Put another way, there is no reason to believe that Pyongyang has deviated from the normal developmental cycle, and achieved some sort of technical breakthrough that would allow it to begin mass production of small nukes for ballistic missiles, or other purposes.

Indeed, for a regime that demands the world's attention, it would seemingly be in Kim Jong-il's interest to produce the biggest possible bang, underscoring the threat posed by North Korea's nuclear arsenal. That requirement would (seemingly) dictate a bigger blast than what was observed last week. While we may never know exactly what transpired at that test site in the DPRK, available evidence hints at a blast that may have been only partially successful. While that development is bad enough, it reminds us that Pyongyang's nuclear program is still in its infancy, and the world community has an opportunity--no, a responsibility--to halt these efforts before it becomes more advanced.

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To give you some idea of how far North Korea has to go in building "better" nuclear weapons, consider these statistics. According to Jane's (and other authoritative publications), a single nuclear warhead from a Minuteman III ICBM has a yield of 330 kt. Warheads on a Trident D-5 SLBM (sub-launched ballistic missile) have a yield of up to 6 mega-tons (MT) each. Tactical nukes actually have a "selectable" yield, allowing them to deliver an explosive force ranging from relatively small, to fairly substantial. By that standard, the device tested by North Korea last week was a veritable pop gun.