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SCIENCE
Comparisons Don’t Support North Korea’s Claims of a
Hydrogen Bomb, Experts Say
By WILLIAM J. BROAD
JAN. 6, 2016
Military experts said comparisons of underground nuclear tests over the past several decades suggested that the North Koreans were
exaggerating their claim on Wednesday to have successfully detonated their first hydrogen bomb.
In 1971, when the United States detonated an H-bomb deep beneath the Alaskan island of Amchitka, the colossal upheaval of
earth that it caused was typical for a class of weapons whose destructive power is roughly a thousand times greater than the atom
bomb that leveled Hiroshima in 1945.
The H-bomb was detonated more than a mile down. Gargantuan shock waves radiated outward, throwing solid rock and dense
earth into bizarre states of fluidity for many miles.
A video of the Alaskan tundra shows hills rising and falling as the giant undulations raced outward. Close-up views show the
ground waves throwing rocks and other objects into the air, tearing apart test-site structures, sending cliffs tumbling into the sea
and opening wide cracks in roads.
The magnitude of the American blast was 6.8. In contrast, South Korea estimated that the bomb detonated on Wednesday had a
magnitude of 4.8 — on the logarithmic scale of earthquake magnitude, an enormous drop in explosive power.
Kenneth W. Ford, an American physicist who worked on the nation’s first hydrogen bomb and last year published an H-bomb
memoir, called the North Korean claim highly suspect. “How could a thermonuclear blast trigger such a weak seismic signal?” he
said. “I agree with the suspicion that it was not a true H-bomb.”
The club of nations that possess thermonuclear weapons has only five known members: the United States, Russia, Britain,
France and China. All are permanent members of the United Nations Security Council.
David Albright, president of the Institute for Science and International Security, a Washington research group, said North
Korea “may be bluffing” in making very large claims for what was actually a small atom bomb. “This possibility,” he said, “should be
carefully considered.”
South Korean experts put the blast’s energy as equivalent to six kilotons of high explosives. In contrast, the atomic bomb
dropped on Hiroshima was nearly three times as powerful, with a force of about 15 kilotons.
Many nuclear experts, including Dr. Ford and Mr. Albright, suggested that the North Korean test might have involved putting a
tiny amount of tritium, or heavy hydrogen, into the core of an atom bomb. Such a technique is known as boosting.
But such a boosted device, by definition, is not a true H-bomb, even though the added thermonuclear reactions can modestly
increase its destructive power.
Philip E. Coyle III, a nuclear expert who directed the Alaskan H-bomb test of November 1971, said the seismic signature of the
North Korean test was “low enough so that it will be difficult to tell if the device was boosted, thermonuclear, just fission or
whatever.”
The world’s largest and most sensitive network meant to detect nuclear blasts, run out of Vienna by the United Nations, uses
hundreds of global sensors to detect underground shock waves, track undersea explosions, sniff the air for telltale radioactivity and
listen for loud sounds in the atmosphere.
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Comparisons Don’t Support North Korea’s Claims of a Hydrogen Bomb, Experts Say - The New Yo...
http://www.nytimes.com/2016/01/07/science/comparisons-dont-support-north-koreas-claims-of-a-h...
The array is designed to detect nuclear blasts as small as one kiloton, or equal to 1,000 tons of high explosives.
Deciphering all the signals can take days to weeks, experts say, and even then the clues might not add up to hard conclusions
since the work of interpretation is often as much of an art as a science. That uncertainty goes especially to small hydrogen bombs,
which seismically can be indistinguishable from atom bombs.
Nuclear experts say ambiguity also surrounds India’s claims to have developed a true H-bomb, based on an underground test in
1998. The reported energy release of that blast was dozens of kilotons — versus the hundreds of kilotons typical of large H-bombs.
In all, India claims six nuclear tests. Pakistan also claims six tests. North Korea now claims four tests.
In an official statement, Pyongyang asserted that its successful H-bomb test meant the nation has now “proudly joined the
advanced ranks of nuclear weapons states.”
A version of this article appears in print on January 7, 2016, on page A8 of the New York edition with the headline: Experts Say Comparisons Do Not Point to
H-Bomb.
© 2016 The New York Times Company
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Why Experts Doubt That North Korea Tested a Hydrogen Bomb - The New York Times
Why Experts Doubt That North Korea
Tested a Hydrogen Bomb
By JOSH KELLER, FORD FESSENDEN and TIM WALLACE JAN. 6, 2016
North Korea claimed on Wednesday that it had tested a hydrogen
bomb, the most powerful kind of nuclear weapon. Related Article
January 6, 2016
North Korea
Estimated 6 kiloton yield
But the yield, or total energy released by the weapon, was close to
that of North Korea’s previous three tests of atomic bombs, which
are simpler.
2006
North Korea
<1 kiloton
2009
North Korea
2 kilotons
2013
North Korea
8 kilotons
It is possible that North Korea tested a boosted atomic bomb, a
weapon whose destructive power is increased by injecting tritium, a
radioactive form of hydrogen. This would be an advance in the
country’s nuclear capabilities.
1951
“Item”
United States
46 kilotons
1953
“Joe 4”
Soviet Union
400 kilotons
http://www.nytimes.com/interactive/2016/01/06/world/asia/north-korea-nuclear-bomb-test.html?_r=0
Why Experts Doubt That North Korea Tested a Hydrogen Bomb - The New York Times
of a hydrogen bomb, and it is not considered a thermonuclear
weapon. Here is the energy released by two large hydrogen bombs.
1961
“Czar Bomb”
Soviet Union
50,000 kilotons
1954
“Bravo”
United States
15,000 kilotons
Sources: South Korean lawmaker Lee Cheol-woo (2016 and 2013), Director of National Intelligence (2009 and 2006), National Resources Defense Council (1951, 1953, 1954 and 1961)
An atomic bomb works by compressing a core of uranium or
plutonium until nuclei in the core split, causing an enormous
explosion. A boosted atomic bomb is similar, but a tiny amount of
tritium at the core makes the weapon more destructive. North Korea
could have tested either of these types of bombs on Wednesday.
http://www.nytimes.com/interactive/2016/01/06/world/asia/north-korea-nuclear-bomb-test.html?_r=0
Why Experts Doubt That North Korea Tested a Hydrogen Bomb - The New York Times
Atom Bomb
Neutron initiator
Starts nuclear
chain reaction
Uranium or
plutonium core
Fissile material
compacts and
explodes.
into the core makes a
boosted atom bomb more
powerful.
Explosive Lenses
Create an inwardly directed shockwave
that compresses the core
The White House said Wednesday that initial data from its
monitoring stations in Asia were “not consistent” with North
Korea’s claim that the test was of a hydrogen bomb, a far more
powerful and technically sophisticated weapon.
Atom Trigger
Small atom bomb explodes
and emits radiation.
Hydrogen
Radiation Case
The high-density casing should
contain and radiate energy
toward the fuel.
Hydrogen Fuel
Thermonuclear fuel is
compressed and explodes.
http://www.nytimes.com/interactive/2016/01/06/world/asia/north-korea-nuclear-bomb-test.html?_r=0
Why Experts Doubt That North Korea Tested a Hydrogen Bomb - The New York Times
North Korea’s Nuclear Testing Site
Test Site
North
Korea
West tunnel entrance
Under construction
North tunnel entrance
Used for tests in 2009 and 2013
South tunnel entrance
Apparently never used,
but under construction since 2009
Nor
th
The New York Times | Source: Jeffrey Lewis, Middlebury Institute of International Studies at Monterey | Satellite Image by CNES / Astrium via Google Earth
Seismic evidence based on triangulating ground waves suggests that
Wednesday’s test occurred at North Korea's Punggye-ri underground
complex, which was also the site of the country’s three previous
nuclear tests.
Nestled in the folds of mountains, the site has a base camp along
with several tunnels, where the tests are thought to be conducted.
Satellite imagery from the past year shows construction work on a
new tunnel in the complex, but it is unclear if that tunnel was used
in Wednesday’s test.
http://www.nytimes.com/interactive/2016/01/06/world/asia/north-korea-nuclear-bomb-test.html?_r=0