Departmental Bulletin Paper EPMAによる火山ガラス組成分析:Na損失の検証と分析条件の提案
Analysis of volcanic glass compositions using WDS-EPMA: Examination of Na Migration and Proposal of Analytical condition

松本, 亜希子  ,  宮坂, 瑞穂  ,  中川, 光弘

78pp.1 - 9 , 2015-03-19 , 北海道大学大学院理学研究院
We examined the analysis method of the compositions of volcanic glass using WDS-EPMA, focusing on Na migration caused by electron-beam bombardment. As a result of the comparison among the beam current in 10 μm square area, it is concluded that Na migration occurs in any cases at 15 kV. During the first 30 seconds, Na decay is not observed, and therefore, the detection of Na must be finished within the first 30 seconds. Considering the variations of other elements, the 15 kV accelerating voltage and 7 nA beam current with raster scanning of 10 μm square area is the best condition for the determination of volcanic glass compositions. This can prevent “grow-in” of Si and Al, as well as can make smaller the deviations of the minor elements. Using this condition, we can discuss the variations of volcanic glass compositions (except for Na) without any corrections.

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