A study of the altitude dependence of the large cosmic-ray showers

Abstract

Assuming primary electrons, the theoretical variation of shower counting rate with altitude has been computed and a comparison made with the observations of Kraybill. Expressed as the ratio to sea level, the observed counting rate has a maximum of 63 as compared to 24 for the theoretical curve. The observed maximum is near 27,000 feet while the computed maximum is at 22,000 feet. Approximations in the calculation and observational uncertainties may make this difference in the elevations of the maxima spurious. The approximations are such as to give too low a theoretical counting rate, but an estimate of the magnitude seems to leave the theoretical maximum counting rate too small by a factor of 1.5 to 2. A computation based upon a mechanism for the multiple production of secondaries by primary protons, which has been proposed by Lewis, Oppenheimer and Wouthuysen, would probably lead to better agreement with the observations. The zenith angle distribution of showers detected by Kraybill’s counters at 30,000 feet has been computed and compared with one determined by Mr. E.W. Cowan from cloud chamber measurements. The theoretical distribution is twice as broad as the observed one. The angular distribution inferred from the altitude dependence observed by Kraybill is in much better agreement with the theoretical than with the cloud chamber distribution. The discrepancy of the cloud chamber observations may arise from the fact that it was only possible to assign a direction to the tracks in 20 to 30 per cent of the photographs.