Less than two percent of the Hiroshima bomb's uranium actually detonated

Little Boy, the nuclear bomb that U.S. forces dropped on the Japanese city of Hiroshima on August 6th, 1945, leveled a two-mile radius of the city, killing an estimated 80,000 people. It was an enormous amount of destruction—and it was caused by less than two percent of the uranium carried by the bomb.

In a recent interview on NPR's Fresh Air, author Eric Schlosser explains just how inefficient this early nuclear bomb was (skip to 11:13 in the recording).

In the case of Hiroshima, the bomb that was dropped on Hiroshima was an incredibly crude and inefficient weapon. When it exploded, about 99 percent of the uranium that was supposed to undergo this chain reaction, didn't. It just blew apart in the air, and a very small percentage, maybe two percent of the fissile material, actually detonated. And most of it just became other radioactive elements. [. . .] Now to imagine how small an amount that is, seven-tenths of a gram of uranium is about the size of a peppercorn. Seven-tenths of a gram weighs less than a dollar bill. So even though this weapon was unbelievably inefficient, and almost 99 percent of the uranium had nothing to do with the destruction of Hiroshima, it was a catastrophic explosion.

As Schlosser puts it, "nuclear weapons since then have become remarkably efficient and small and capable of destruction that makes Hiroshima seem trivial." Given the stories of false alarms, nuclear accidents, and harrowing near-disasters contained in Schlosser's book, and the reports of shaky security in the U.S.'s nuclear arsenal, it's enough to make you wish humanity had never figured out how to make these weapons in the first place. [NPR]

Image: AP photo of Little Boy


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