Cosmic-Ray Intensities at Great Depths

Abstract

A fourfold Geiger-Müller tube telescope was employed to count the relative number of cosmic rays under different thicknesses of rock. Each Geiger-Müller tube consisted of a 0.125 mm tungsten wire anode and a cylindrical copper cathode 9 cm in diameter and 71 cm in length sealed in a glass envelope filled with hydrogen to a pressure of 9.6 cm of mercury. The experiment was performed in a mine whose shaft was inclined at an angle of 34° from the horizontal. Counts were made at thirty-nine different stations at depths from zero to 1408 meters of water equivalent, where the rate was 5.7×${10}^{-5\mathrm{}}$ as great as at the surface. When the intensity is plotted against the depth, the resulting curve shows no points of inflection. The effective absorption coefficient decreases from 0.07 per meter of water at the surface to 0.0025 at the greatest depth. If the logarithm of the intensity is plotted against the logarithm of the depth, two straight lines, one from 20 to 250 and the other from 250 to 1418 meters water equivalent from the top of the atmosphere, represent the data well. Shower counts were also made at ten of the stations. These also show a bend at 250 meters. This suggests that there may be two types of very penetrating rays both capable of producing showers. It may be that one of these consists of "heavy electrons" and the other of "neutrinos."