The Properties of Cosmic Radiation in the Lower Atmosphere

Abstract

Experiments performed previously with apparatus carried to very high altitudes by free balloons have been conducted in the lower portion of the atmosphere. Two different instruments were operated in a B-29 airplane, and at Mt. Evans, Colorado. Absorption curves in lead, up to a thickness of 18 cm, were obtained at 14,260 feet, 25,000 feet, and 30,000 feet. Intensity vs. altitude curves for the lower regions of the atmosphere may now be combined with those for very high altitudes without an arbitrary normalization. A direct comparison has been made between the present measurements and those of others regarding the relative change of intensity between sea level and Mt. Evans, and the absorption in lead at Mt. Evans. Factors for the conversion of all of the data to absolute intensities have been determined utilizing a $\gamma$-ray howitzer method for measuring the effective length of a G-M counter. Satisfactory agreement is noted between values of the absolute intensity previously measured by others at sea level and at Mt. Evans, and those reported herewith. The absolute intensity of cosmic-ray particles near the "top of the atmosphere" at geomagnetic latitude 52°N is given as 10.1±0.20 particles/min./${\mathrm{cm}}^2$/unit solid angle. Consideration is given to the considerable error which may be introduced in the comparison of measurements of the "total" intensity at very high altitudes obtained with different G-M counters.