Hiroshima_ The World's Bomb - Andrew J. Rotter [8]
While a neutron likes to stay put, it is, as a result of its electrical neutrality, an ideal projectile with which to enter and explore the nucleus. Probing the nucleus with a neutron, especially the large nucleus of one of the heavier and less stable elements, instantly destabilizes it. This nucleus busting, this breaking of atoms, is called fission. It was first observed by Otto Hahn and Fritz Strassmann in a laboratory in suburban Berlin in late 1938, properly interpreted by Lise Meitner and her physicist nephew Otto Frisch at the year’s end (Hahn was inclined to resist the implications of his own experiment), confirmed experimentally by Frisch, then published in the February 1939 issue of the journal Nature, and even before that disclosed by Bohr at a meeting of the American Physical Society in Washington— from which excited physicists departed early in order to try the experiment themselves, and on which more later.
Holding together the protons and neutrons (the nucleons) is the strong nuclear force, which means that large amounts of energy are locked up inside the atom’s nucleus. When a projectile neutron strikes a target nucleus, the nucleus breaks apart, yielding two nearly equal halves, a burst of energy, and some its own neutrons. ‘These fly through the rest of the material,’ Bronowski explains, ‘and if the piece is large enough each neutron is certain to strike another nucleus and thus set off another burst of energy—and fire off still other neutrons to carry on the reaction.’ The materials most likely to sustain such a chain reaction (as it is called) are those with heavy, unstable, neutron-rich nuclei, particularly uranium and human-made plutonium. A gram of uranium, fully fissioned through such a chain reaction, produces enough energy to light 20,000 light bulbs for ten hours. A similarly fissioned pound of uranium makes as much energy as millions of pounds of coal. Near the culmination of this process comes the release of radiation in the form of beta particles and gamma rays.6
Certainly Ernest Rutherford, the nucleus around whom buzzed an electron cloud of other scientists, had not, despite his puckish comment about a fool in a laboratory blowing up the universe, set out to make a powerful explosive. Anyone claiming that the day of atomic power was dawning was ‘talking moonshine’, he wrote dismissively in 1933. The excitement of discovery was thus not tied to some cataclysmic result, and for this reason not circumscribed by the nation. Even during the First World War, Rutherford had stayed in touch with scientists throughout Europe, including those in Germany. When the war ended, cooperation redoubled; what the American J. Robert Oppenheimer called the ‘heroic’ days of atomic physics, the time of ‘great synthesis and resolutions’, occurred during the 1920s, when the world was at peace. In the great centers of interwar physics—Cambridge, Paris, Copenhagen, Gottingen—there was excitement about theory, tiny particles of matter and their puzzling behavior, and how to reconcile the evidence recorded on machines and with the eyes with what one knew, or thought one knew, about the way atoms worked. In 1914, the writer H. G. Wells published a novel called The World Set Free, in which the earth, forty years hence, was a place of atomic-powered cars and radioactive bombs made of an element Wells called ‘Carolinum’, which bored deep into the soil and fired off ‘puffs of heavy incandescent