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N. Korean threat increases with possibility of miniaturized nuclear weapons

North Korea went ahead with its sixth nuclear test on Sept. 3 despite repeated sanctions from the international community, with a detonation far more powerful than its previous one.

With the reclusive state extending the range of its ballistic missiles while rapidly developing nuclear weapons, it now poses a far greater threat than in the past. In the meantime, it appears that the international community has been left with a sense of powerlessness when it comes to preventing the country from developing such weapons.

In a broadcast at around 3 p.m. on Sept. 3 local time, about three hours after the nuclear test, North Korean news presenter Ri Chun Hee declared in a strong voice that the North had successfully tested a hydrogen bomb with a level of power on a practically unprecedented scale. The news broadcast said that leader Kim Jong Un, chairman of the Worker's Party of Korea, had signed the order to carry out the test.

According to the Japan Meteorological Agency (JMA), North Korea's previous five underground nuclear tests produced earthquakes with magnitudes ranging between 4.9 and 5.3. The magnitude of the tremor from the latest test was 6.1, making it around 10 times stronger, by conservative estimates, than the previous test in September 2016, which produced a magnitude-5.3 temblor.

Japan's Defense Minister Itsunori Onodera said that the scale of the latest detonation was estimated at about 70 kilotons, which would be a record high.

Tetsuo Sawada, an assistant professor at Tokyo Institute of Technology, who specializes in nuclear engineering, touched on the fact that the quake from the latest test recorded by the JMA was nearly one whole point higher than that of the previous test, saying, "From the size we can assume that it was a hydrogen bomb." However, it is difficult to actually verify whether it was a hydrogen bomb or not. Sawada points out that verification requires detection of helium-3, which is produced during nuclear fusion. Since helium-3 is lighter than air, it quickly spreads into the atmosphere, so detection becomes harder as time passes, Sawada says.

When North Korea conducted its fourth nuclear test in January 2016, it claimed that it was an experimental hydrogen bomb. But for reasons including the relatively small scale of the explosion, U.S. experts took the view there was a high possibility it was not a fusion-type hydrogen bomb like those possessed by the United States and Russia, but a boosted fission bomb that uses a small amount of fusion fuel to increase the yield of the fission reaction.

Tatsujiro Suzuki, director of the Research Center for Nuclear Weapons Abolition (RECNA) at Nagasaki University, commented, "There is a high possibility this time that it was another boosted weapon."

In any case, the technology to produce boosted weapons would allow North Korea to miniaturize its nuclear warheads, and load them onto intercontinental ballistic missiles (ICBMs).

"It probably wants to secure nuclear deterrence as early as possible to ward off a pre-emptive attack by the United States," Suzuki conjectured.

Soon, 11 years will have passed since North Korea's first nuclear test on Oct. 9, 2006. The country is beefing up its nuclear arsenal at a rapid pace. Pakistani nuclear physicist Samar Mubarakmand, who led Pakistan's nuclear weapons test in May 1998, said that as of February 2013, Pakistan was developing about one nuclear bomb every six months. Abdul Qadeer Khan, who has been nicknamed Pakistan's "father of the atomic bomb" and who provided uranium enrichment technology to North Korea in the late 1990s, praised North Korea's nuclear technology, writing that North Korea's nuclear bomb designs were more advanced than Pakistan's.

North Korea has rapidly developed nuclear weapons and ballistic missiles with the United States in its sights. "With the latest ICBMs, North Korea could fit them with multiple bombs, and have them head to several different places at the same time. There is now a taste of reality to full deployment," Sawada says.

U.S. missile experts have said North Korea's missiles lack accuracy, but with higher explosive power they become harder to intercept -- so a nuclear attack would still be effective even if the nuclear weapon exploded slightly off target. By acquiring the technology to produce powerful nuclear weapons along with its ballistic missile technology, the threat North Korea poses to the United States increases dramatically.

In June last year, North Korea started testing ballistic missiles on lofted trajectories. Yoji Koda, former Maritime Self-Defense Force Fleet commander, analyzes its move as follows: "The assumption is that they've nearly perfected an object that's going to be made to re-enter the atmosphere, and there has arisen a need for them to acquire relevant data. It probably means that over the year from September last year, they've been near completion of a miniaturized nuclear warhead that can be fitted onto the Hwasong-14 (ICBM)."

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