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High altitude tests on the geographical, directional, and spectral distribution of cosmic rays

Millikan, R. A. and Cameron, G. H. (1928) High altitude tests on the geographical, directional, and spectral distribution of cosmic rays. Physical Review, 31 (2). pp. 163-173. ISSN 0031-899X. doi:10.1103/PhysRev.31.163.

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Intensity of cosmic rays in the high Andes.—Depth-ionization readings taken in Lake Miguilla, Bolivia (alt. 4570 m) and on Lake Titicaca (3820 m) agreed closely with observations in the northern hemisphere previously reported. Intensity of cosmic rays at sea-level.—Three electroscopes which differed considerably in form, wall material and volume, all agreed in giving at sea-level an ionization of 1.4 ions/cc/sec. Effect of Milky Way on cosmic ray intensity.—Two sets of day and night observations, each of three days duration, in a deep valley of the Andes at 4700 m elevation failed to bring to light any difference between the radiation coming in from the plane of the Milky Way and the plane normal thereto. Spectral distribution of the cosmic rays.—A new curve which includes the readings in South America and those published in 1926, analyzed by the method before used, yields absorption coefficients which vary from μ=0.25 per meter of water to μ=0.15. The corresponding wave-lengths, using the Compton equation, are .000525A and .00032A. Ionization at extreme altitudes.—Under the assumption that the largest absorption coefficient, viz. μ=0.25, is valid for the upper regions of the atmosphere, the ionization at any altitude may be calculated, with the aid of the Gold tables, taking the sea-level value as 1.4 I/cc/sec. The total ionization, computed from this data by a graphical integration, for the Millikan and Bowen sounding-balloon observations reported in 1926, shows remarkable agreement with their experimental result. This implies that the wave-lengths of the rays entering the atmosphere are not appreciably different from those at altitudes at which we have ourselves taken observations. Effects of thunder-storms on cosmic rays.—Lake Miguilla, Bolivia, is completely screened from thunder-storm influences and yielded the same value of the cosmic rays as regions not so screened. Also sea-level observations taken in the midst of heavy thunder-storms showed no influence of these on cosmic ray readings.

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Additional Information:©1928 The American Physical Society. Received 7 November 1927.
Issue or Number:2
Record Number:CaltechAUTHORS:MILpr28a
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2316
Deposited By: Tony Diaz
Deposited On:27 Mar 2006
Last Modified:08 Nov 2021 19:46

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