A Study of Cosmic-Ray Bursts

A "fast" ionization chamber, suitable for the investigation of cosmic-ray bursts, is described. The operation of the chamber and of the associated electronic circuits is discussed. The nature of the cosmic-ray events responsible for the production of ionization bursts was studied (a) by observing coincidences between several ionization chambers, (b) by analyzing the shape of the ionization pulses, (c) by operating an ionization chamber inside a cloud chamber which was expanded whenever the ionization chamber recorded a pulse. The experimental results led to the following conclusions: (1) at mountain altitudes 98 percent of the ionization pulses in an unshielded chamber of the type used are produced by nuclear disintegrations, the remaining 2 percent by air showers; (2) in the nuclear disintegrations, heavily ionizing particles of sufficiently high energy are produced to cause coincidences between neighboring chambers; (3) nuclear disintegrations are produced mainly by non-ionizing rays, which are possibly neutrons, certainly not photons; (4) about 12 inches of lead is necessary to reduce the intensity of the radiation which produces nuclear disintegrations to $\frac{1}{e}$ times its original value.