The author determined the radon contents of spring waters in the eastern part of Hiroshima Prefecture. In this district granite is distributed, and radon was found in most of the spring waters, although their content was variable. The results are as follows: 1) The highest radon content was 172 Mache (626×10(-10) Curie/ℓ) of Harada Spring. Such a high mdon content is rare in the spring waters of Sanyo District. 2) Kanae Spring showed 73.2 Mache (266.4×10(-10) Curie/ℓ) and the well waters near by it showed also comparatively high radon content. 3) The radon contents of the springs of Niwakayama, Immyoseki and No.1 of Hongo, and Takasu water were 44.6 (162.3), 23.2 (84.5), 7.5 (27.3) and 14.7 (53.5) Mache (×10(-10) Curie/ℓ) respectively. 4) The radon contents of rain, river and sea waters could not be determined by the I. M. fontactoscopeon account of its low values.

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