Measurement of the Ionization Per Centimeter of Path by Individual Secondary Cosmic Rays

Abstract

The paper describes measurements of the ionization caused by individual secondary cosmic rays and groups of rays in a vertical cylinder 15 cm high and 7.5 cm in diameter. The experimental results are represented by plotting $F\left(n\right)\mathrm{}$ against $n$, where $F\left(n\right)\mathrm{dn}$ is the number of rays or groups passing through the cylinder in an assigned time and giving rise to spurts containing between $n$ and $n+dn$ pairs of ions. If $f\left(l\right)\mathrm{dl}$ is the number of rays of path length between $l$ and $l+dl$, the theoretical curve for $f\left(l\right)\mathrm{}$ for single rays shows a discontinuous increase at a value of $l$ equal to the length of the cylinder, and this is followed by a sharp decrease. This phenomenon enables one to ascertain on the $F\left(n\right)\mathrm{}$ curve the value of $n$ which corresponds to the length of the cylinder, and so to deduce the ionization per centimeter of path in spite of the existence of multiple rays and of unavoidable amplifying tube background. The value for argon comes out as 89 ions per centimeter at atmospheric pressure. This value includes the contribution cited by G. L. Locher as caused by the Auger effect. The corresponding values for nitrogen and oxygen are 61 and 57, respectively. By a further analysis of the results, and particularly of those giving simultaneous spurts of ions with two cylinders in line, the existence of multiple rays is actually verified. These rays contribute two-thirds of the total ionization observed in the cylinder, and constitute one-third of the total number of ionizing entities, groups and singles. By a consideration of their effects it is possible to reconstruct the high values obtained for the apparent ionization per centimeter of path by former observers who have deduced their values from ionization measurements combined with counter data and from fluctuation measurements.