Word: fission
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Puzzle to Fission. Late in 1938 a distinguished German chemist named Otto Hahn, of Berlin's Kaiser Wilhelm-Institute, was bombarding uranium with "slow" neutrons of low energy. As one of the end products, he identified barium. This puzzled him, but he published a diffident note on it in Naturwissenschalfen...
...just about to leave for Princeton. Bohr told U.S. experimenters about it. They sprang to their atom-smashing machines and quickly confirmed it (TIME, Feb. 6, March 13, 1939). They also stood gallantly back while Dr. Meitner published the first notes on uranium splitting. She called it "fission," a familiar word in biology but a new term for physics...
Energy Profit. Fission was revolutionary, sensational-not only because the heaviest of all elements had been cracked wide open, but because of the tremendous energy profit. Up to then, scientists had always had to put more energy into their projectiles than was released in the breakup. Now, an explosion of about 200,000,000 electron-volts was touched off by idling neutrons of less than one electron-volt. Matter equal to about one-fifth of a neutron's mass was converted into energy according to the Einstein formula...
Explosive Calculations. Before the war it was discovered that slow-moving neutrons could split the atoms of the uranium isotope, U-235, giving a mighty gush of energy. Besides energy, their "fission" produced more flying neutrons. If enough of these in turn split uranium atoms, the reaction would maintain itself, gain momentum. It would flash through all the uranium, like the flame of a match through excelsior...
Centrifuges. The three-way split will not put atomic power to work tomorrow. The only promising kind of uranium for neutron-splitting or "fission" is the isotope called U-235.- This kind is scarce and extremely difficult to separate from the common isotope, 11-238. So far, not enough U-235 has been isolated to put in a fruit fly's eye. A Swedish scientist was beginning to speed up the process with gadgets called thermal diffusion tubes when the war stopped him. Another line of attack is with centrifuges - whirling machines which work like cream separators...