The plutonium bomb was dropped on Nagasaki on August 9th 1945, three days after a uranium bomb had destroyed Hiroshima.
Was it a plutonium bomb, like the ones it tested in 2006 and 2009, or one that used highly enriched uranium?
The material that went into Fat Man, the plutonium bomb detonated over Nagasaki, was made at Hanford, which at its peak consisted of nine nuclear reactors and five plutonium reprocessing plants.
They were not so sure about the more complex "Fat Man" plutonium bomb, so they tested it in the desert of Alamogordo, New Mexico, before dropping one on Nagasaki on Aug. 9.
The site produced plutonium for the bomb dropped on the Japanese city Nagasaki and continued producing plutonium for the US nuclear arsenal for years.
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Iran is also building a heavy-water reactor that could produce plutonium, another bomb ingredient.
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It hastened the end of World War II, which concluded within a week after the dropping of a plutonium-based bomb on Nagasaki on Aug. 9.
One of its reactors produced plutonium for the atomic bomb dropped on Nagasaki, Japan, in 1945.
The latest revelation shows an accelerating effort that also includes work to produce plutonium, another potential bomb ingredient (see article).
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That move prompted Britain, France and Germany to discontinue negotiations aimed at persuading the Iranians to abandon for good their ambitions to enrich uranium and make plutonium (another potential bomb ingredient).
Officials trying to stem nuclear proliferation used to congratulate themselves that only a very few of the known incidences of trafficking involved the sort of uranium and plutonium useful for a bomb.
Yet suspicions have mounted as Iran has invested in expensive technologies for enriching uranium and making plutonium (both possible bomb ingredients) before having a civilian nuclear-power industry that can make peaceful use of them.
Yet their rivalry is fuelling the fastest, most dangerous build-up of bomb-usable plutonium and uranium anywhere.
Such assistance to Syria was only prevented from translating into an indigenous source of bomb-ready plutonium for that state-sponsor of terror by an Israeli air force attack last September.
At issue is a 1994 deal between North Korea and America, under which the North agreed to freeze and then dismantle its plant for making bomb-usable plutonium (inspectors had discovered that it had made more than it had owned up to, but still do not know how much).
Mr. GRAHAM ALLISON (Harvard University): During those three years, the North Koreans produced more plutonium, worked on their nuclear bomb test, worked on their missiles, tested their missiles.
In 18 instances small amounts of bomb-grade uranium or plutonium were involved.
Extrapolating from the amounts of bomb-grade uranium and plutonium each is thought to possess, India may have up to 95 nuclear weapons and Pakistan up to about 50 (see table), though possibly both have far fewer.
Ukraine, Canada, Chile, Mexico and Kazakhstan were among those promising to dispose of bomb-usable enriched uranium or plutonium on their soil.
But the North didn't need more plutonium because it also has a secret program to enrich uranium for a bomb.
This traded annual supplies of heavy fuel oil, and eventually two western-designed nuclear reactors, for North Korea's agreement to shut down its own plutonium-rich reactor, whose fuel rods could have been reprocessed into bomb cores.
When weapons designers have an idea to boost the yield from a small amount of plutonium, or come up with a faster way to fuse atoms in a hydrogen bomb, they build a prototype for testing.
When that deal collapsed in 2002 after America confronted North Korea with evidence of its cheating secretly buying equipment to enrich uranium (another bomb ingredient) Mr Kim tossed out inspectors, extracted the plutonium from the rods and says he built bombs with it.
He compared them with Barringer, and later with the collapsed holes above underground nuclear-bomb tests (where he had been sent prospecting again, this time for plutonium).
But the United States and its allies have asked it to give up the plutonium it already has, an estimated 30 kilograms, as well as details of any other bomb-producing programs.
Though North Korea openly admits making nuclear weapons using plutonium, it has still not come clean about its pursuit of the uranium route to the bomb, even though Pakistan's former chief nuclear scientist, Abdul Qadeer Khan, has reportedly said he sold Mr Kim's regime some uranium-linked nuclear secrets.
The guess is that, if constraints were lifted, Iraqi scientists could build a nuclear bomb within about five years, and sooner if they could buy the highly enriched uranium or plutonium required.
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