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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