New Methods of Determining the Absolute Intensity of Cosmic Rays in the Atmosphere and the Residual Ionization in Ionization Chambers

The portable Gish-Sherman ionization meter in connection with four geometrically similar cylindrical ionization chambers of different size was used for determining (1) the cosmic-ray intensity at sea level when the apparatus is completely shielded from local radiations by 10 cm of iron, and (2) at the same time a value for the residual ionization produced by spurious alpha-particles from the walls of the chambers. Two methods to obtain this end are described: one using all four chambers, and the other using the largest chamber and varying the pressure of the filling gas. Plotting the observed ionization versus the ratio of surface: volume gives a straight line which, when extrapolated for infinite volume leads to the value representing the ionization produced by cosmic rays without the secondaries from the wall.