Narrow Cosmic-Ray Showers

It has been found that the cosmic-ray particles which occur in showers of small angular divergence are much more penetrating than those of the usual type of shower. The particles in such "hard showers" are clearly not electrons and are interpreted as medium and low energy mesotrons. The second maximum of the Rossi curve, which is accentuated for small-angle shower arrangements, can be accounted for in terms of such showers, produced by mesotrons. Hard showers are present also in the first maximum, probably being produced in this case by the soft component. In the first maximum 34 percent of the narrow showers are ascribed to ionizing primaries, as compared to 75 percent in the second maximum. The number of rays per hard shower is found both by counter and cloud chamber experiments to be small, in most cases, two. Present theory can account for the production of such mesotron showers, though some modification must be introduced regarding the limitation in angular spread of the emitted particles. Maier-Leibnitz and others have obtained evidence for the relatively frequent production of slow, absorbable mesotron secondaries. Because of the much higher rate of production of these mesotrons as compared with those of the hard showers, a different mode of formation may be present; speculation on this point is at present premature.