Foote, R. 5S. Time Variation of Terrestrial Gamma Radiation adams, J. A. S. and Lowder, W. M. (Editors) Natural Radiation Environment Univ. of Chicago Press, Chicago (1964) Thompson, T. and Wiberg, P. A, Some Observations of Variations of the Natural Background Radiation Tellus, 15, 313 (1963) ‘mination of Kraner, H. W., Schroeder, G. L. and Evans, R. D. Measurements of the Effects of Atmospheric Variables on Radon-222 Flux and Soil Gas Concentrations tesearch Group I sjht in the ’. mental 3) Univ. (1963) Program M. of Chicago Press, Chicago Johnston, A. (Editors) (1964) R. The Absolute Cosmic-Ray Ionization in the Atmosphere at Balloon Altitudes Thesis, re 2 Adams, J. A. S. and Lowder, W. Natural Radiation Environment Calif. Inst. of Tech. (1956) National Academy of Sciences Studies in Penetration of Charged Particles in Matter NRC Publication 1133 (1964). Hess, V. F. and Manning, A. W. A Study of the Ionization Produced in Various Gases by Cosmic Radiation otal Absorptia ) sptember (1963 i 1lin, J. E. y to B-Ray : Transactions, American Geophysical Union, 37, December (1956) Clay, J. The Absolute Value of Cosmic-Ray Ionization at Sea Level in Various Gases Rev. Mod. Phys. ll, 123-127 (1939). Hopfield, J. J. Use of Argon in the Ionization Method of Measuring Cosmic Rays and Gamma Rays Phys. Rev., 43, 675-686 (1933) eR Ee

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