Cosmic-Ray Measurements with a Small Ionization Chamber II. Comparison of Small Bursts at Different Altitudes and Their Variations with Thickness of Shield

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Abstract
Measurements of bursts produced in a small ionization chamber (230 cc volume) have been carried out at several stations. A comparison is made between frequencies of occurrence of various sized bursts at Cambridge, Mass. (bar. 76), Echo Lake, Colo. (bar. 51.1), Mt. Evans, Colo. (bar. 44.7), and Cerro de Pasco, Peru (bar. 45.4). The altitude ratios for burst groups comprising 10-19 rays, 20-29, and 30 and greater, are: Echo Lake to Cambridge, 4.9, 8.0 and 8.8; Mt. Evans to Cambridge, 7.3, 14.3 and 20.0. The data for the smallest burst groups are in agreement with counter measurements on showers, while the ratios for the largest bursts agree with the ionization chamber data of others on large bursts. The maxima of the burst production absorption curves shift to greater lead thicknesses with increasing burst size.