Artificial Radioactivity

In Paris, not far from the Pantheon, is a crooked little byway once called the Rue des Postes. From that byway last week came two words in a combination new to physicists the world over: artificial radioactivity.

Science has long been aware of the little street once called the Rue des Postes. Its present name is the Rue Pierre-Curie. In a shabby wooden building at its end, 36 years ago, Mme Marie Sklodowska Curie and her husband Pierre discovered radium.

At that time their daughter Irene was in swaddling clothes. Eight years later bearded, brooding Pierre Curie was killed by a truck. Now Mme Curie, twice a Nobel Prizewinner, devotes her time to managing the Institut du Radium's Curie Laboratory, which she founded in 1912, and lecturing at the University of Paris. The old wooden building where she once worked is gone. But in one of the Institute's new buildings on the same street Irene, with her brilliant husband Jean Frederic Joliot, continues to pry into matter's secrets in much the same way Father & Mother Curie did before her.

It cannot be said that the young Curie-Joliots discovered neutrons, elusive, electrically inert particles 1,845 times as heavy as electrons. Neutrons were produced incognito by them and other researchers. Dr. James Chadwick of Cambridge University's famed Cavendish Laboratory first proclaimed neutrons for what they were (TIME, March 7, 1932). The Curie-Joliot work on radiation was a stout prop for Dr. Chadwick, and his proclamation was confirmed by the French couple who experimentally showed that neutrons behaved as only electrically dead particles could (TIME, Aug. 1, 1932). Hailed in every physical journal in the U. S. and Europe, their work foreshadowed discoveries to which their title would be clear.

Unquestioned was the priority and importance of last week's announcement from the Rue Pierre-Curie. With alpha particles, which for more than a decade have been used to bombard vulnerable substances, the Curie-Joliots attacked boron. The expected neutrons hopped out instantly. But positrons (positive electrons) shot out also, and kept on shooting out after the bombardment stopped, as though the boron had been stimulated into a state of radioactivity. After 15 minutes the positrons were still darting out 30% as fast as at first: after 30 minutes 9% as fast; after 45 minutes 2.7%. Theoretically the radiation, though soon dwindling beyond the recording point, would never quite expire. A curve representing it would be a parabola approaching but never quite touching its asymptote.

This, according to the researchers, is probably what happens: The attacking alpha particle joins a boron atom to form a neutron (which flies off) and an unstable nitrogen atom which in a few seconds or minutes changes to a carbon atom with the release of a positron. Hence, just as the spontaneous radioactivity of radium turns it finally into lead, the end-product of boron's artificial radioactivity is carbon. Not only boron but magnesium and aluminum became radioactive under similar treatment.

The Curie-Joliot report stirred Lord Rutherford, director of Cavendish Laboratory, to begin confirming experiments. Said he, "It is remarkable that the life of the unstable atom produced is as long as it is. We do not know whether the atoms so far made artificially radioactive are typical or whether other unstable atoms which may be produced will have a longer or shorter life. The discovery of the Joliots shows how little we really know about radioactivity."

Dr. Henry Askew Barton of the American Institute of Physics pointed out the possibilities for cancer therapy. Instead of inserting costly radium capsules into malignant tumors, doctors may soon use substances made radioactive artificially.

Educated first in a private scientific school founded by her mother, whose Slavic features she has, Irene Curie-Joliot snapped up a science degree at the University of Paris. When her second child was born two winters ago she was away from the workshop only a month. She and M. Joliot get up at 5:30, write their papers ("What a burden!"), are glad to reach the laboratory at 9. They keep long hours, find no time for theatres and concerts. For three months in summer they leave the atom in peace, take the children to grandmother Curie's place on the Brittany coast. There is never a thought of dividing scientific credit. Husband and wife work like one person with two heads, four hands, 20 fingers. "We compare notes," says M. Joliot, "and exchange our thoughts so constantly that we honestly don't know which of us is the first to have an original idea. Don't you agree, ma chere?"

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