Science: Three Prizes

Last week the Swedish Royal Academy of Science awarded its 1936 Nobel Prize for Chemistry to a profound student of molecular structure, Professor Peter Joseph Wilhelm Debye, 52, of Berlin’s Kaiser Wilhelm Institute for Physics. The Prize for Physics was divided between a pioneer cosmic ray researcher, Professor Victor Franz Hess, 53, of Austria’s Innsbruck University, and 31-year-old Professor Carl David Anderson of California Institute of Technology, discoverer of a fundamental particle of matter, the positiveelectron. Prizeman Debye will receive about $40,000, Prizemen Anderson & Hess each half that sum.

Dr. Debye has done powerful work on the conduction of electricity by salt solutions, the electrical properties of insulators, the heat capacities of solids, the atomic architecture of molecules. He was one of four men who turned the crystal diffraction grating invented by Max von Laue into a precise instrument which, by combing X-rays through the atomic lattice in the crystal, determines the composition of a mixture as exactly as by chemical analysis. In Pittsburgh last September Chemist Debye pointed out to the American Chemical Society that water has a quasi-crystalline structure, therefore resembles a diamond more closely in arrangement than it resembles its own gaseous form, steam. “We are just beginning to know what water is,” he said wryly, “although we have been calling it H2O for more than a century.”

Dr. Hess was the first man to see clearly that the cosmic rays were cosmic—that is, that they did not come from the earth or the atmosphere. Enthusiastic Austrians once called this mysterious radiation “Hess Rays,” just as an enthusiastic U. S. scientist later called them “Millikan Rays.” Cosmic rays, as almost everyone now knows, bombard Earth continuously from every direction in the sky. No one knew this when the 20th Century opened. About that time it was observed that some sort of radiation from somewhere was constantly ionizing the air in electroscopes. Some theorists thought the source was radioactive material in the ground. If this were so, the radiation should have fallen off markedly at short distances above ground. By carrying instruments up in balloons, Hess, Gockel and Kolhörster killed off the terrestrial radioactivity theory. In 1911 Hess made seven flights to 3,000 ft., found no decrease in the rays whatever. Later, nearly six miles up, he found them seven times stronger than on the ground. “A radiation of very high penetrating power,” he wrote, “enters our atmosphere from above.”

In 1934, still on the job, Dr. Hess aimed his recorders at the exploding star Nova Hercules (TIME, Dec. 31, 1934) to see whether, as some cosmologists had suggested, such stellar blow-ups could be a source of cosmic rays. He did detect a slight increase in cosmic ray intensity from the direction of the nova, but too small to be of definite significance.

Dr. Anderson discovered the positive electron under curious circumstances. He was not looking for it, and its existence had already been foreshadowed by a British theorist only three years older than he was.

Five years ago Cambridge University’s brilliant Paul Adrien Maurice Dirac, then 29, declared that some of the problems facing physics were so tough that experimental tools would soon be blunted against them. For sharper tools he relied on his mathematical brain and a pencil. It was his idea to develop, generalize and perfect mathematical language, express something in it, then look into Nature for the thing that had been expressed.

The sort of electrons then known were fundamental particles about 1,850 times smaller in mass than a hydrogen atom, and carrying a negative electric charge. Dr. Dirac reasoned that these tiny bundles of electricity would seek the lowest energy states they could find. In the world of experience they might range through innumerable energy states down to zero. In the world of mathematics they might go below the zero level, as through a magic mirror, into the realm of minus energy. All electrons might get into this fantastic domain if it were not for the Pauli exclusion principle which holds that no more than one electron can occupy any one energy level. When all the minus states are filled there must be some electrons left with their burdens of plus energy.It is these “plus” electrons that enable people to switch on lamps, listen to their radios, talk over the telephone. The others, so long as they are submerged in the sea of minus energy, must remain unobserved.

Dr. Dirac imagined what would happen if a cosmic ray or gamma ray (high-powered photon) happened to hit one of these submerged electrons and transfer to it some of the ray’s energy—perhaps a million electron-volts. It would be hoisted willy-nilly out of its minus nonentity into an observable state of plus energy. Since this would leave a minus energy state unoccupied, that vacant “hole” would be discernible as a contrast against the uniform background of occupied states. By contrast with electrons of minus energy and negative electric charge, the “hole” would have to be an electron of plus energy and positive electric charge. Christening this hole-particle the “anti-electron,” Dr. Dirac stated that its life would be exceedingly brief. In an infinitesimal fraction of a second, it would encounter an ordinary electron, the electron would drop into the hole, and with a flash of light the two would disappear together in the minus energy sea.

Mystics found this theory exciting, but no hard-headed experimenters started looking for the “anti-electron,” the little particle with the positive charge. It was far from the thoughts of young Dr. Carl David Anderson on Aug. 2, 1932. That day, as part of a big cosmic ray program organized by his chief, Robert Andrews Millikan, he was gambling with his Wilson cloud chamber and with expensive photographic plates.

The interior of a Wilson chamber is saturated with water vapor. If the chamber’s piston is suddenly pulled out, the lowered pressure causes supersaturation for a moment, and if an ionizing agent such as a cosmic ray happens to be passing through just then, vapor will condense on the ions, leaving a track of fog particles which can be photographed. If Dr. Anderson happened to yank his plunger at just the right moment, he would find ion tracks on his pictures. Nineteen times in 20 he could expect to draw a blank.*

Dr. Anderson was maintaining a strong magnetic field across the chamber which would curve the paths of flying electric particles. By the direction of curvature he could tell whether they were positively or negatively charged. He had also shrewdly inserted a lead plate in the chamber. A particle which passed through this plate would be weakened by the passage, hence more sharply curved on the far side by the magnetic field. Thus the physicist could tell which way it had traveledalong the track.

After developing one of his plates Anderson saw that he had scored a hit. To the untrained eye there was nothing but a ragged little white line. But to Anderson that line was astounding. It was thin and sketchy like the path of an electron. The particle had obviously traveled upward along the track and not downward, because it was more strongly bent above the lead plate. Also it had curved to the left. In that magnetic field only a positively charged particle could be traveling upward and curving to the left. In all features the particle was the “anti-electron,” the mathematical “hole” imagined by Dirac. Its life was brief—about a third of a millionth of a second. But Karl Kelchner Darrow of Bell Telephone Laboratories later pronounced it “probably the most famous individual corpuscle in the history of physics.” Dr. Anderson called his discovery the positive electron, or positron.

Forecaster Dirac won a Nobel Prize in 1933. Positrons have now been produced at the rate of 30,000 per second by gamma rays, and the Curie-Joliots of Paris observed them shooting out of light-weight elements in their first experiments with artificial radioactivity. It has even been suggested, despite their brief lives in the laboratory, that positrons may be a component of the primary cosmic rays.

Robert Andrews Millikan, who measured the electric charge of the negative electron, won a Nobel Prize in 1923. Visibly moved was grey-haired Dr. Millikan last week when he heard that his young co-worker was to join him in the highest honor that Science can bestow. Asked by newshawks to say something about his “outside interests,” Nobelist Anderson grinned: “In my younger school days my ambition was to become a track star, a high jumper. But it didn’t work, and now my hobby is tennis. I just couldn’t jump high enough.”

*Since then Wilson chambers have been so rigged that the ionization caused by the passing ray operates a mechanism which automatically pulls the piston at the right moment.