富士火山およびその周辺地域の環境放射能強度分布と湧水中のラドン濃度

Abstract

The environmental gamma radiation from basaltic lava flow units and the radon concentration in ground waters around the Fuji volcano were measured with a portable liquid scintillation counter newly developed for field survey. Gamma-ray spectrometry was carried out on some lava samples with a Ge(Li) spectrometer. The observed environmental radioactivites ranged from 88 to 170 cpm, being lower than the values of ordinary andesitic lavas, for example, 190-220 cpm for the Asama volcano. This is consistent with the Th- and U-series radio-activities and K contents of the lavas from the Fuji volcano which may be incorporated into the group of lower values among gamma-ray spectrometric results so far obtained for Japanese Quaternary volcanoes. The Th-series/K, the U-series/K and the Th-series/U-series ratios of the Fuji volcano are 1.9, 2.9 and 0.7, respectively, each falling within the range observed for the Izu-Mariana volcanic arc. The radon concentration in ground water around the Fuji volcano was in the range of 0.1-0.6 × 10-10Ci/l

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