PARIS — Was North Korea's nuclear device a partial dud?

That is one of several theories that Western experts say might explain the apparent low explosive force of the communist nation's first declared nuclear test.

Other suppositions are that North Korea deliberately chose a small device to save its limited stocks of bomb-making plutonium or that it somehow muffled the shockwaves from the underground blast to make it appear smaller than it was.

Even if North Korea got helpful pointers from nuclear-capable Pakistan, as many experts suspect, the technology of efficiently splitting atoms to make a controlled explosion is still tricky for novices to master. For North Korean scientists, working largely in isolation, that could be especially true.

"The devil is in the details," said French nuclear proliferation expert Bruno Tertrais. "It's like cooking. The fact that you have the recipe does not make you a chef."

One explanation could be that the device — if nuclear — fizzled rather than truly banged, with the plutonium only partially detonating, he said. Or, the device's timing may have been slightly off, creating a weaker chain reaction with less explosive force than planned.

But because of the intense secrecy that shrouds North Korea, it may never be known exactly how large an explosion it was hoping for and, therefore, whether the test was successful, as it claimed.

"I think they got a partial result," said Philip Coyle, a senior adviser to the Center for Defense Information, a think tank in Washington.

"For them it was enough ... to say that it was a success. It helps them to claim that they are a nuclear power, and that the world should take them seriously, which is what they want. But I wouldn't be surprised if after several months they don't try again."

He said North Korea may have muffled shockwaves from the device by detonating it in a very large underground cavity.

A sparsity of knowledge about the test site's geology — a factor that can affect the spread of shockwaves — also complicates the efforts of scientists overseas who are poring over seismic data and other readings to try to pinpoint the exact nature of the blast.

According to Hankyoreh, a South Korean newspaper that has good ties with the communist North, a North Korean diplomat in China acknowledged Tuesday that the nuclear test caused a smaller blast than expected, but he also claimed that Pyongyang had the ability to detonate a more powerful device.

"The success in a small-scale (test) means a large-scale (test) is also possible," the unidentified diplomat said in comments posted on the newspaper's Web site.