Smallest Thing

When a smallest thing is discovered it must be observed more than once to be believed. In February, Cambridge University's Dr. James Chadwick proclaimed the existence of the neutron, new smallest thing (TIME, March 7). With the proton (positive electricity), electron (negative electricity) and photon (light particle), this made four smallest things. But the neutron is elusive, hard to find. It contains no detectable electric charge. It leaves no marks in the form of ionized or electrified particles when it passes through a gas. Having no charge, it is not repelled by charged atoms. Hence it has a high penetrating power. It can shoot through a mile of air, compared with an alpha particle's few inches. It can shoot through several feet of lead. And last week scientists had new assurance that it existed, from the laboratories of Mme Marie Curie in Paris.

Among those who have been bombarding atoms with alpha particles are Mme Curie's daughter, Irene Curie-Joliot, her husband F. Joliot, Dr. Chadwick and Professor Walter Bothe of Giessen, Germany. Professor Bothe, bombarding beryllium, decided he was creating an artificial super-gamma ray. Dr. Chadwick decided that a proton and an electron knocked loose by alpha particles might combine, without any electrical charge at all, in one unit to make a neutron. This self-contained unit might be the ultimate unit of magnetism, having within itself opposite poles.

By repeated experiment it is known that any electrically charged form of matter will penetrate paraffin, for example, more easily than lead. Bombarding lithium with alpha particles from polonium, the Curies found they were knocking out a ray that penetrates lead more easily than paraffin. By empirical reasoning, the ray produced must be a new kind of ray, since it breaks all known rules. The Curies concluded their ray "cannot be of an electronic or electromagnetic nature." It is probably a ray of neutrons. Irene Curie-Joliot and her husband did much of the preliminary work in radiation that helped Neutron-Discoverer Chadwick. Mme Curie-Joliot, 35, looks faintly like Actor John Barrymore.

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