including some of the surrounding small islands like Rongerik, Rongelap, and Utirik. In terms of energy released (usually measured in TNT equivalence), Castle Bravo was about 1,000 times more powerful than each of the atomic bombs that were dropped on Hiroshima and Nagasaki during World War II. Castle Bravo is the sixth largest nuclear explosion in history, exceeded by the Soviet tests of Tsar Bomba at approximately 50 Mt, Test 219 at 24.2 Mt, and three other (Test 147, Test 173 and Test 174) ≈20 Mt Soviet tests in 1962 at Novaya Zemlya. High yield The yield of 15 megatons was triple that of the 5 Mt predicted by its designers. The cause of the higher yield was an error made by designers of the device at Los Alamos National Laboratory. They considered only the lithium-6 isotope in the lithium-deuteride secondary to be reactive; the lithium-7 isotope, accounting for 60% of the lithium content, was assumed to be inert. It was expected that the lithium-6 isotope would absorb a neutron from the fissioning plutonium and emit an alpha particle and tritium in the process, of which the latter would then fuse with the deuterium and increase the yield in a predicted manner. Lithium-6 indeed reacted in this manner. It was assumed that the lithium-7 would absorb one neutron, producing lithium-8, which decays (through beta decay into beryllium-8) to a pair of alpha particles on a timescale of nearly a second, vastly longer than the timescale of nuclear detonation. However, when lithium-7 is bombarded with energetic neutrons with an energy greater than 2.47 MeV, rather than simply absorbing a neutron, it undergoes nuclear fission into an alpha particle, a tritium nucleus, and another neutron. As a result, much more tritium was produced than expected, the extra tritium fusing with deuterium and producing an extra neutron. The extra neutron produced by fusion and the extra neutron released directly by lithium-7 decay produced a much larger neutron flux. The result was greatly increased fissioning of the uranium tamper and increased yield. Summarizing, the reactions involving lithium-6 result in some combination of the two following net reactions: n + Li → H + He + 4.783 MeV Li + H → 2 He + 22.373 MeV But when lithium-7 is present, one also has some amounts of the following two net reactions: Li + n → H + He + n Li + H