PARIS: Scientists took a dour wait-and-see attitude after North Korea claimed to have successfully conducted a nuclear test on Monday.

Only careful analysis of data returned by seismic or atmospheric sensors will say whether the blast was a success or a damp squib, they said.

Nor could they rule out the possibility of a scam, in which North Korea blew up a huge stock of conventional explosives to bolster its claim to have joined the nuclear club.

James Acton of Vertic, an independent non-governmental organisation (NGO) in London that specialises in verification research, noted enormous discrepancies in the estimated size of the blast.

The Korea Earthquake Research Centre in South Korea said there was a 3.58-magnitude tremor from North Korea’s North Hamgyong province that translated into the equivalent of 800 tonnes (0.8 of a kilotonne) of TNT.

But Russian Defence Minister Sergei Ivanov, quoted by the ITAR-TASS news agency, said the strength was five to 15 kilotonnes.

By comparison, “Little Boy,” the US atomic bomb which destroyed Hiroshima during World War II released the equivalent of around 12,500 tonnes of TNT.

“I’ve heard from three different sources that it (the North Korean blast) was less than one kilotonne,” said Acton, a nuclear physicist by training.

“This (the Russian figure) is not a difference of 10 or 20 per cent (in the yield). It’s huge. We should wait to see if that Russian statement is confirmed,” he said.

Acton said that going for a 15-kilotonne yield was “the natural size” for a country trying to test a nuclear weapon. Paradoxically, it is easier to make and test a Hiroshima-sized arm of this size rather than to make a smaller one, which requires mastery of important miniaturisation techniques.

“If it turns out to be less than a kilotonne, it could look very much like a fizzle,” a bomb that failed to detonate properly and achieve a full chain reaction, Acton told AFP.

Another theoretical possibility is that North Korea stashed lots of TNT underground and blew it up.

“It is possible to tell the difference between a conventional explosion and a nuclear test,” said Acton. “The differences are very fine and subtle, and you need time to analyse the signatures.”—AFP