Word: fissionable
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...normally emits neutrons at a steady rate, 2) graphite, which slows neutrons down but does not absorb them, and 3) cadmium, which absorbs neutrons very effectively. As the control rods were withdrawn-so the experimenters figured-fewer of the neutrons from the uranium would be absorbed, and therefore more fission would occur. At some point of withdrawal, fission would be producing new batches of neutrons faster than the cadmium would be absorbing them. Result: a chain reaction...
...Just as his ship was about to leave Copenhagen, two German refugee physicists, Lise Meitner and O. R. Frisch, rushed aboard with a dismaying report. They had just heard that German Chemists Otto Hahn and Fritz Strassmann in Berlin had split the uranium atom. This was atomic fission, and with it the Nazis might soon be able to build an atomic bomb...
...miles to the U.S. The Russians had made great gains in putting a bigger punch into a smaller package (weight-yield ratio), thus could increase either the range or power of existing weapons systems. They had approached perfection in a clean bomb. (In some of their blasts, the fission trigger-which is the main source of a bomb's radioactivity-formed only 2% of the explosive yield.) They were able to fire warheads that survived the punishment of re-entry into the atmosphere, something the U.S. had not even tried. Most significant, their high-altitude tests indicated work...
...authorities, including the Atomic Energy Commission, the Public Health Service and the Weather Bureau, feel sure that the 1962 fallout will probably equal or exceed the 1959 peak, but they are not alarmed. The fission energy yield of the Soviet 1958 tests was 10 to 15 megatons. The total energy of last fall's Soviet tests was much greater (170 mega tons), but most of it came from nuclear fusion, which creates little fallout. Only about 25 megatons came from nuclear fission of uranium or plutonium, and since many of the Russian tests were exploded at high altitudes, their...
...develop "clean" hydrogen bombs with little or no radioactive fall out by improving the efficiency of the fission "trigger" that produces most of the fallout in nuclear explosions...