広域火山灰の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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Non-destructive gamma-ray spectrometry was made on the following widespread volcanic ashes for specific radioactivities of U- and Th-series nuclides and for K contents ; (1) 1978 Sakurajima ash fall samples collected at 6 different distances (4-42 km) from the crater, (2) 1982 Asama ash fall samples collected at Karuizawa (Nagano) and Tokyo, (3) Rhyolitic ash fall deposit from the N3 layer in Izu-Oshima island, (4) "AT" ash (Aira Tn volcanic ash) deposit at an outcrop near Gotemba (Shizuoka) and (5) Akahoya volcanic ash fall deposit from northern Kyushu. Detailed examination of the data for each ash fall and for some related volcanic pro-ducts showed that there was no significant difference in three ratios, Th-ser./U-ser., Th-ser./K and U-ser./K, between the ashes scattered far away in the air and such materials deposited near the crater as lavas, pyroclastic flow deposits and pumice fall deposits. As observed previously with samples occurring near their sources, these parameters tend to cluster around values characteristic of respective volcanoes.
特定非営利活動法人日本火山学会の論文
1983-10-01