Carl D. Anderson

Unraveling the Particle Content of Cosmic Rays

I understand my task is to report on the part played by cosmic ray research in providing new information on the particles of physics, until such work was gradually driven into oblivion by the advent of the new accelerators. Because of my health, I have not had access to a library except under very trying and difficult circumstances, and hence this paper was prepared at my home, based wholly on a limited amount of material and my own recollections. This has inevitably tended to make for omissions in the paper, to make it less objective and more personal than it otherwise might or should have been. I regret the omission of the contributions provided by the extensive programs of research by Geiger-counters, ionization chambers, and the extremely important results from the photographic emulsion techniques originally devised by Cecil Powell, and later continued by many other investigators. In particular, I regret the omission of the innovative and important series of experiments carried out by Bruno Rossi beginning about 1930 based mainly on the adaptation of Geiger counter techniques to a study of the complex character of the cosmic radiation. His results as well as those of other investigators have had a strong influence on my thinking, and were very helpful in interpreting some of our own results.

Mesotron (Intermediate Particle) as a Name for the New Particles of Intermediate Mass

THE existence of particles intermediate in mass between protons and electrons has been shown in experiments on the cosmic radiation1. Since at present so little is known concerning the properties of these particles, for example, the exact value of the mass, the laws governing their production, their stability against disintegration, etc., it may yet be too early to assign to them a name. But inasmuch as several names have already been suggested, namely, dynatron, penetron, barytron, heavy electron, yukon and x-particle, it may be wise to consider the matter at this time.