North Korea's government bragged Wednesday that it had tested "a smaller H-bomb," calling it the "H-bomb of justice."

White House spokesman Josh Earnest, however, counters that initial analysis "is not consistent with the North Korean claims of a successful hydrogen-bomb test."

Earnest did describe the blast as a nuclear test, making the one this week North Korea's fourth. And Melissa Hanham, a Canadian expert on North Korea with the James Martin Center for Nonproliferation Studies in Monterey, Calif., told CBC News that it was "pretty much universally acknowledged it was a nuclear test, but there's a lot of skepticism about whether it was an H-bomb test."

The South Korean military also doubts it was an H-bomb test, according the South Korea's Yonhap news agency.

Hanham says when, and if, radionuclide data from the explosion becomes available, experts should have a pretty good idea of just what kind of explosion it was. That could take anywhere from two weeks to two months.


North Korean leader Kim Jong-un watches a firing contest of the KPA artillery units at undisclosed location. (KCNA/Reuters)

While Hanham says an H-bomb explosion "is a much more complicated kind of explosion to execute," McMaster University physicist Cliff Burgess notes H-bomb technology is "similar to what they're mastering with the atomic bomb."

He's not saying the technological leap is trivial, but points out that the North Korean weapons designers would be working on technical issues similar to those involved with the development of their atomic bomb.

A-bombs versus H-bombs

There are some key differences between atomic bombs and hydrogen bombs. In basic terms:

  • An A-bomb relies on fission, the splitting of atoms.
  • An H-bomb relies on fusion, which produces energy through combining light atoms to make heavier ones.
  • A fission bomb uses an ordinary explosion to bring together enough uranium or plutonium to create a critical mass, which causes a much, much bigger explosion.
  • A fusion bomb uses a fission explosion to compress hydrogen, making it very dense and hot, so that the hydrogen atoms fuse rather than fly apart, also causing a much larger explosion.

Burgess says that all the big nuclear powers developed hydrogen bombs, "partly because it's do-able once you've got the infrastructure to make the atomic bomb." 

Assessing North Korea's test claims are complicated by the fact that while a fully developed H-bomb is more complex than a basic atomic bomb, there are variations of atomic bombs that incorporate hydrogen.

"Ready to detonate an H-bomb'

In December, North Korean leader Kim Jong-un described his country as, "a powerful nuclear weapons state ready to detonate self-reliant A-bomb and H-bomb." 

That month, while writing that his own government considered Kim's statement a bluff, Konstantin Asmolov, an expert on Korea at the Russian Academy of Sciences, wrote that "the term 'H-bomb' implies a range of weapons, some of which are rather basic, and well within the current level of North Korean technical and scientific development."

Asmolov's point is that a nuclear weapon can still be considered an H-bomb, even if it doesn't use an ordinary nuclear weapon to ignite a hydrogen fusion reaction and a much bigger explosion.

What's called a boosted fission weapon could technically fit the definition of an H-bomb since it uses hydrogen to speed up the fission reaction. This produces a bigger explosion, although nowhere near as big as a fully developed H-bomb.

To put this in context, the unit for measuring H-bomb explosions — the megaton — is a thousand times bigger than the kiloton unit used to measure A-bomb and boosted fission weapon explosions.

According to the Comprehensive Nuclear-Test-Ban Treaty Organization, this week's explosion in North Korea measured "essentially the same" as a nuclear test conducted at the same location in 2013, the Punggye-ri Nuclear Test Facility, in  mountainous terrain in the northeast of the country.

Hanham's reasons it wasn't an H-bomb test

North Korea's statement describes its H-bomb test as a "spectacular success" but Hanham says she doubts Wednesday's blast in North Korea could have been a full H-bomb test.

Melissa Hanham

Melissa Hanham, an expert on North Korea with the James Martin Center for Nonproliferation Studies, says, 'Almost no one thinks North Korea is at a point in their development where they could do an H-bomb test.' (Middlebury Institute of International Studies)

The explosion wasn't big enough, according to the seismic data. A good thing, too, she says, since the Punggye-ri test site couldn't have contained the explosion if it was a real H-bomb, nor is she aware of evidence the country had prepared the site for such a test.

The U.S. and Russia do have relatively small H-bombs in their nuclear arsenals, but developing those weapons is more technically challenging than building a big H-bomb. The superpowers developed their big bombs much earlier than the smaller, tactical weapons.

Hanham hypothesizes that the country definitely wants to have an H-bomb, but it is probably experimenting with some kind of boosted nuclear device. However, she does note the slight possibility that it was a failed test in which only the fission reaction went off, without initiating the fusion reaction.

Hanham adds that as far as her research has determined, there aren't the indicators that North Korea has reached a point in its technological development where it could detonate a full H-bomb. But if the radionuclide data does indicate that North Korea conducted a boosted atomic test, Hanham says that will mean North Korea has advanced its nuclear program, and that "they're further down the line" towards achieving their goal of developing a real H-bomb.

She points out that, "For North Korea, these tests aren't just scientific tests, in many ways they're political tests and they are meant to give a signal to the outside world, and also to appear strong to their domestic audience."

Which may be why North Korea's official statement about the test contains this verbal flourish, "Nothing is more foolish than dropping a hunting gun before herds of ferocious wolves."

Video produced in December 2015 by the James Martin Center for Nonproliferation Studies.