1983 年三宅島溶岩の U 系列核種と Th 系列核種の比放射能および K 濃度

概要

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U- and Th-series radioactivities and K contents of basaltic rocks erupted in 1983 from the Miyake-jima volcano are measured by a non-destructive gamma-ray spectrometry. The K contents show an essentially uniform distribution throughout the lava flow and the scoria fall deposits, giving the average value of 0.46%. The Th-series specific activities are all very low, mostly clustering around 0.2×10^<-13>Ci/g. The U-series activities generally range from 1.0 to 1.5×10^<-13>Ci/g, some varying up to 2.4×10^<-13>Ci/g. The Th- to U-series activity ratios cluster, with a few exceptions, around 0.20. The lowermost ends of the lava flow appear to have significantly low Th-series/U-series values. An initially erupted portion of the magma might have a different history with respect to some radionuclides.
特定非営利活動法人日本火山学会の論文
1984-12-28