The Day We Lost the H-Bomb: Cold War, Hot Nukes, and the Worst Nuclear Weapons Disaster in History

Some elements, namely those with more than 209 protons and neutrons, are so big that no amount of glue can hold their nucleus together. These heavy elements are naturally unstable and regularly shed bits of themselves, or “decay,” to become smaller and more stable. Scientists call these unstable elements “radioactive.” Probably the two most famous radioactive elements are those used in the atomic bombs of World War II, uranium and plutonium (or, more specifically, their highly fissionable isotopes, uranium-235 and plutonium-239). Scientists found that they could speed the disintegration by bombarding the uranium and plutonium nuclei with neutrons. When they did this, the nuclei split and released two or three neutrons and more energy. If additional uranium or plutonium atoms were nearby, the neutrons could blast their nuclei apart as well, releasing more neutrons and causing more fission. This reaction will eventually peter out, unless there is enough radioactive material placed closely enough together to sustain the reaction. If a “critical mass” of uranium or plutonium — about 110 to 130 pounds of uranium-235 or 13 to 22 pounds of plutonium-239—can be piled together, the number of neutrons released will increase in each generation. This leads to a chain reaction of atom splitting and a nuclear explosion.

Plutonium is more radioactive than uranium and more difficult to handle. But during World War II, uranium manufacturing moved slowly. The Manhattan Project scientists would have enough uranium-235 for only one weapon by 1945. If they wanted more bombs, they would have to build them from plutonium.

To build the bomb, metallurgists took a mass of plutonium and cast it into a hollow sphere. Then engineers created a shell of high explosive around the plutonium. In theory, if they detonated the high explosive from many different points at the same time, it would implode, crushing the plutonium into a solid ball. Hopefully, the squeezed plutonium ball would achieve critical mass and lead to a nuclear explosion. Few Manhattan Project scientists believed this design could work. “No one had ever used explosives to assemble something before,” Richard Rhodes explained in Dark Sun, his history of the hydrogen bomb. “Their normal use was blowing things apart.” Such a precise, perfectly timed explosion seemed implausible. The Navy captain in charge of explosives research said that the task was like trying to implode a beer can “without splattering the beer.” But the implosion bomb did work, first at the Trinity test near Alamogordo, New Mexico, on July 16, 1945, and then over Nagasaki on August 9, 1945. The bomb over Nagasaki, “Fat Man,” reportedly used about 13.7 pounds of plutonium, for a yield of 23 kilotons. It was about 17.5 times as efficient as the Hiroshima bomb.

Even before the Trinity test, at least one Manhattan Project physicist was already looking ahead.

Edward Teller had taken charge of the implosion group in January 1944, but increasingly he turned his thoughts to fusion. Maybe, he thought, the immense heat of a fission bomb could ignite a lump of deuterium, making a fusion bomb possible.

Teller, it turns out, was right. Finally, here was a source of energy powerful enough to trigger a fusion reaction. But the engineering problems were daunting, making an imploding beer can seem like child's play. Engineers had to design a bomb that could contain a fission explosion long enough to trigger fusion, then keep the fusion going long enough to get a good yield before the whole bomb assembly disintegrated. Yet by 1952 they had figured it out. On November 1 of that year, the United States exploded a hydrogen bomb on Eniwetok Atoll, about three thousand miles west of Hawaii.

The test, code-named “Mike,” yielded 10.4 megatons, nearly seven hundred times the power of the Hiroshima bomb. Mike vaporized the island of Elugelab and killed everything on the surrounding islands, leaving a crater more than a mile wide. If it had been dropped on New York City, it would have obliterated all five boroughs. For the physicist Herbert York and many others, the Mike test heralded the beginning of a more dangerous world: “Fission bombs, destructive as they might have been, were thought of [as] being limited in power. Now, it seemed we had learned how to brush even these limits aside and to build bombs whose power was boundless.” The hydrogen bomb lying in the riverbank outside Palomares was called a Mark 28. The Mark 28 could be assembled in five different variants for a range of configurations and yields. This particular Mark 28 was a torpedo-shaped cylinder that weighed about 2,320 pounds. The bomb had entered the arsenal in 1958, and by May 1966, the United States had produced 4,500 of them.