Might-Have-Been

Last year Manhattan newspapers suddenly sprouted sensational stories about a gigantic explosion which, it seemed, had not happened simply because of good luck. Had it happened, every building in New York City and every ship at its docks--not to mention its people--would have vanished without a trace. A crater would have been blown in the earth 100 miles across, and the sea would have poured into this vast pit from southern Connecticut halfway to Philadelphia. Cause of this might-have-been catastrophe: some well-intentioned physicists at Columbia University who were cracking uranium atoms with neutrons as contentedly as small boys crack nuts.

Science popularizers like to point out with bated breath that there is enough atomic energy locked in a cupful of water to drive a big liner across the Atlantic. To hardheaded physicists, the idea of releasing and harnessing this energy was a wild dream. Then, early in 1939, Hahn and Strassmann of Germany, with help from France, Sweden and Denmark, used neutrons to break uranium atoms into two nearly equal fragments, with release of some 200,000,000 electron-volts of atomic energy per atom (TIME, Feb. 6; March 13). This was by far the most violent atomic explosion ever effected by human agency.

Heavy atoms like uranium had been chipped before, but not cracked in two. Moreover, the most effective agents for splitting or "fission" of uranium were "slow" neutrons with initial energies of only a fraction of one electron-volt, so that the energy profit from one fission was enormous.

Dozens of research teams thereupon started a mass attack on uranium. It was soon learned that the explosions produced two or more neutrons in addition to the uranium fragments. These two neutrons might possibly crack two more uranium atoms, producing more neutrons and more fissions, thus culminating in a continuous, self-propagating explosion. It was the prospect of this "chain reaction" that started the nightmare of the explosion that would have blown New York City to kingdom come.

Last week Science Service of Washington broadcast word from Paris that a chain reaction had been accomplished there. But Paris had not even quivered--for the reaction was not a multiplying one but a diminishing one, died out after a few stages.

The physicists who accomplished the feat were Nobel Prizewinner Jean Frederic Joliot, son-in-law of the late Marie Curie (see p. 24), L. Kowarski, H. von Halban Jr., E. Perrin. Details of the experiment were meagre: apparently they split uranium atoms in such a way that a lot of neutrons flew out--entirely too many to be accounted for as the result of the first fissions. Some of the neutrons must have been products of secondary and tertiary fissions. After that the reaction was too weak to continue. But it was obvious that the release of atomic power is immensely nearer realization.

Lest the news from Paris terrify timid people, Physicist John Ray Dunning of Columbia said that fission experimenters now believe there is an automatic check against a multiplying chain reaction getting out of control. The accelerating release of atomic energy would heat up the uranium specimen; this heat would speed up the neutrons beyond the point of maximum effectiveness for fissions, and the reaction would therefore slow down, and stop.

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