Determination of the Intensities of Low-ZComponents of the Primary Cosmic Radiation atλ=41°Using a Čerenkov Detector

A measurement of the intensities of the low-$Z$ components of the primary cosmic radiation has been made in the upper atmosphere at a depth of 13 g/${\mathrm{cm}}^2$ by means of a "Skyhook" balloon flown at $\lambda =41.5\mathrm{}°$. The measuring instrument consisted of a thin (3.0 g/${\mathrm{cm}}^2$) Čerenkov detector placed within the solid angle of a Geiger counter telescope. A Čerenkov detector was used because of its unique discrimination against slow particles. A system of guard and shower counters and circuits was included to identify side showers and background events occurring in the detector. A vertical intensity of 82±9 alpha particles/${\mathrm{meter}}^2$ steradian sec, at the top of the atmosphere was obtained, based on 374 counts attributed to alpha particles. Data obtained as the balloon rose to altitude gave a value of 43±8 g/${\mathrm{cm}}^2$ for the apparent absorption mean free path of alpha particles in air. An upper limit was set on the intensity of primary protons at this depth. In addition, a small number of counts that could be attributed to particles with $3\le Z\le 5$ were obtained and are discussed.