Abstract
WE have recently made measurements of cosmic ray intensities in the Simidu tunnel of the Government Railways of Japan. The measurements were carried out at different positions along its length of 9.7 km., in order to find the penetration of cosmic rays through various thicknesses of rocks, which consist mainly of diolite, the average density being probably 2.8. The measuring apparatus was the Neher electroscope1 with which Dr. Millikan kindly supplied us. The ionization chamber of diameter 15 cm. was covered with 11 cm. of lead and was left at each place for about 24 hours. The vertical thickness of rocks varied from 1,230 m. to 120 m., corresponding to about 3,400 m. and 340 m. of water-equivalent respectively.
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References
Cf. R. A. Millikan and H. V. Neher, Phys. Rev., 50, 15 (1936).
W. Kolhörster, Sitz. Pr. Ak. Wiss., 689 (1933); NATURE, 132, 407 (1933). A. Corlin, NATURE, 133, 63 (1934); Ann. Observatory Lund, No. 4, A, 95 (1934).
loc. cit.
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NISHINA, Y., ISHII, C. A Cosmic Ray Burst at a Depth equivalent to 800 m. of Water. Nature 138, 721–722 (1936). https://doi.org/10.1038/138721b0
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DOI: https://doi.org/10.1038/138721b0
