Trail's End

For a comparatively young man (he is 32), amiable, dimple-chinned Dr. Carl David Anderson of California Institute of Technology has accomplished a great deal in science. In 1932 he snapped the first picture of a positive electron. For this discovery he won the highest honor Science can bestow, a Nobel Prize. His pioneer positive electron photograph has become historic. In the Physical Review last week, Prizeman Anderson printed a snapshot of another kind of particle which may also become historic.

The existence of "heavy electrons," also known as X-particles or barytrons, was suspected by Anderson and his co-workers in 1934, and later discovered almost simultaneously by him and Drs. Jabez Curry Street & Edward Stevenson of Harvard. These queer little particles appear to originate about ten miles above the earth's surface as a result of collisions between primary cosmic ray particles and air atoms. Calculations of their mass have yielded figures from 110 to 400 times the weight of an ordinary electron.

Lately Dr. Anderson and his lean young coworker, Dr. Seth Neddermeyer, have been trying to trap barytrons near the end of their ranges--that is, as they slow up from exhaustion of energy after many collisions. The two physicists have a "cloud chamber" filled with argon, helium and alcohol vapor. A particle passing through knocks ions (electrified fragments) out of the gas atoms, and the vapor condenses on the ions, making a visible track which shows up as a white line in photographs. A device called a coincidence circuit snaps the picture when the particle passes through.

The picture printed last week is not the first barytron track to be photographed, but it is the best and perhaps the most unmistakable. Furthermore, it shows this cosmic particle "dying"--i.e., coming to rest in the gas. This was a rare piece of scientific luck but also a reward for patience.

Dr. Anderson's analysis of the photograph (see cut) is as follows: the particle, weighing 240 electron units, enters the chamber near the upper left-hand corner of the picture, making a thin, sketchy white track which is slightly curved owing to a strong magnetic field maintained across the chamber. Its energy is 10,000,000 electron-volts. It passes through a copper cylinder (left centre) and emerges below, much weaker and making a broader line. Its energy is now only 210,000 volts and so its path is more sharply bent by the magnetic field. After traveling about an inch more (to the right) it comes to a dead stop.

Evidence which does not appear clearly in the picture convinced Dr. Anderson that at the end of its trail the particle disintegrated by the emission of a positive electron.

This file is automatically generated by a robot program, so reader's discretion is required.