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"Layer Cake" Test


On August 20, 1953, the Soviet press announced that the USSR had tested a hydrogen bomb. Eight days prior in Kazakhstan, the explosive device “Joe-4” put to the Soviet developed “layer cake” design to the test. The bomb technology received its name due to its alternating layers of a fusion fuel, consisting of lithium-6 deuteride with tritium, and a fusion tamper, uranium. Results of the explosion seemed to indicate the device as more similar to a powerful fission bomb than an actual hydrogen bomb. The test’s explosion yielded the equivalent of 400 kilotons of TNT, making it 30 times larger than the atomic bomb dropped on Hiroshima. It was also small enough to fit in a plane and therefore, unlike “Mike" the American thermonuclear device tested a year earlier, it was not limited and could easily be turned into a deliverable weapon.

Initial Soviet research into the H-bomb followed closely the path the U.S. scientists were pursuing. The work was conducted by a group in Leningrad led by Iakov Zel'dovich that had been given access to information provided by atomic spy Klaus Fuchs. This included a detailed description of the "classical super" design, physicist Edward Teller's original idea for a super bomb. Zel'dovich's team began calculations on the basis of this information. But in 1948, Igor Kurchatov, director of the Soviet nuclear program, set up a second team to investigate the feasibility of the H-bomb. Its assignment was to check the Zel'dovich group's calculations.

Andrei Sakharov was a member of this second team. Before long, he had come up with an innovative new scheme. He suggested a "Layer Cake" design, which would consist of alternating layers of hydrogen fuel and uranium. High explosives surrounding the "Layer Cake" would be used to implode and ignite an atomic bomb at the center of the device. The atomic explosion would heat and compress the hydrogen fuel sufficiently to cause a fusion reaction. The fusion reaction in the hydrogen would lead to the emission of high energy neutrons which would in turn create further fissioning in the uranium.

Another talented young physicist Vitalii Ginzburg's came up with what Sakharov called the "Second Idea." Initially Sakharov suggested that the hydrogen fuel should consist of a mixture of deuterium and tritium, both of which are isotopes of hydrogen. Ginzburg suggested using lithium deuteride instead, a compound of lithium and deuterium, which has the advantage of being a solid at room temperature. In addition, it would produce tritium during the course of the explosion. Kurchatov understood immediately that Ginzburg's idea was a breakthrough and he arranged to have lithium deuteride produced on an industrial scale.

The first test of the "Layer Cake" took place on August 12, 1953. Four days earlier, one of the Soviet leaders, Georgii Malenkov announced to the Supreme Soviet that the U.S. no longer had a monopoly in hydrogen weapons. The scientists, who were already at the test site heard the speech on the radio. And in his memoirs, Sakharov noted that Malenkov's announcement would have "raised the tension if we had not already been keyed up to the maximum."

Just a few days before the detonation, the scientists realized that fallout from the blast might seriously injure people living in the surrounding area. At the last minute, the military commander organized an evacuation; some of those removed from their homes couldn't return for 18 months.

Kurchatov was in charge of the test and gave the order for the countdown. A witness gave this account of the blast: "The earth trembled beneath us, and our faces were struck, like the lash of a whip, by the dull, strong sound of the rolling explosion. From the jolt of the shock wave it was difficult to stand on one's feet. A cloud of dust rose to a height of eight kilometers (five miles). The top of the atomic mushroom reached a height of twelve kilometers (seven and a half miles), while the diameter of the dust of the cloud column was approximately six kilometers (almost four miles). For those who observed the explosion from the west, day was replaced by night."
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