Atom Crackers

The size and shape of an invisible barn might be determined by throwing a million baseballs at it and studying the number of balls which hit it and the angles at which they bounce off. That is the way physicists have determined the structure of the atom. Pellets have been radium particles, X-rays and, lately, cosmic rays. Inability to control available ammunition has been the great handicap.

Last week three young Carnegie Institution men, Drs. Merle Anthony Tuve, Lawrence R. Hafstad and Odd Dahl, through the Physical Review, offered atom crackers a new, manageable howitzer. (They had first mentioned that piece of laboratory ordinance when the Association for the Advancement of Science met in Pasadena last June. Although the scientists could see little of the machine's effect, they nonetheless gave a $1,000 prize to the ingenious young men.) Their machine consists essentially of a tesla coil under oil and a cascading cathode tube. The coil builds up an electrical potential to 3,000,000 volts. That enormous power is suddenly dumped into what is basically a series of X-ray tubes ending in a mica window.

In 1930 the three young men projected radium's beta (high speed electrons) and gamma (penetrating X-rays) rays out of that mica window. Left for duplication were radium's alpha particles, the nucleus of helium.

The helium nucleus of four protons is clumsy chain-shot for atomic bombardment. Drs. Tuve, Hafstad & Dahl now surpass radium by shooting single protons from their gun. By means of a cloud chamber they are now able to see and photograph the stream of protons from their machine. The effect looks like a stubby shaving brush with bristles 1.6 in. long. Each bristle is the path made by a proton only one 10,000th of null millionth of an inch in diameter.

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