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A more accurate and more extended cosmic-ray ionization-depth curve, and the present evidence for atom-building

Millikan, Robert A. and Cameron, G. Harvey (1931) A more accurate and more extended cosmic-ray ionization-depth curve, and the present evidence for atom-building. Physical Review, 37 (3). pp. 235-252. ISSN 0031-899X. doi:10.1103/PhysRev.37.235.

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The cosmic-ray ionization-depth curve has been extended at both its upper and lower ends and made more accurate throughout. The absorption coefficients obtained directly from the slope of the curve run from μ=0.35 per m. of water at the top (Pike's Peak) to μ=0.028 at the bottom (80 m. or 262 ft. of water below the top of the atmosphere, thus bringing to light both softer and harder components than the authors had before found. Strong quantitative evidence is presented, on the basis of the Klein-Nishina formula, that the strongest and most absorbable cosmic-ray band arises from the act of formation of helium out of hydrogen. Striking qualitative evidence is found that the three more penetrating bands are due to the formation out of hydrogen of the only other abundant elements oxygen (C, N, O) silicon (Mg, Al, Si, S) and iron (Iron group). Two independent proofs are given that the cosmic-rays enter the earth's atmosphere as photons, namely, (1) they are quite uninfluenced by the earth's magnetic field, and (2) the ionization produced by them in a closed vessel does not increase continually in going to the top of the atmosphere but passes through a maximum. It is shown to follow that the cosmic rays, in coming from their place of origin to the earth have not passed through an amount of matter that is appreciable in comparison with the thickness of the earth's atmosphere and that they must therefore originate in interstellar space rather than in the atmospheres of the stars. Some participation of the nucleus in the absorption of cosmic-rays is brought to light.

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Additional Information:©1931 The American Physical Society. Received 9 December 1930. We wish to express our appreciation to Professor Bowen for assisting, as indicated above, in the analysis of the curve.
Issue or Number:3
Record Number:CaltechAUTHORS:MILpr31a
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:6558
Deposited By: Tony Diaz
Deposited On:13 Dec 2006
Last Modified:08 Nov 2021 20:35

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