走査型X線分析顕微鏡(SXAM)による非破壊•連続化学組成分析の猪苗代湖湖底堆積物コアへの適用

摘要

Measured values of twelve elements analyzed by scanning X-ray analytical microscope (SXAM) have been evaluated by comparing them with that of conventional X-ray fluorescence spectrometry analysis (XRF). The samples used were powder-pressed pellets of the GSJ (Geological Survey of Japan) geochemical reference samples and Lake Inawashiro-ko lacustrine sediments. The chemical compositions obtained by the SXAM were quantified by fundamental parameter (FP) method with one standard spectrum. The measured values of titanium, aluminum, iron, manganese and potassium by the SXAM are consistent with a recommended value of the GSJ geochemical reference samples, and fulfill a level comparable to that of the XRF FP-method analysis. The quantifications of silicon, magnesium, calcium and sulfur have a systematic deviation from the recommended values of the GSJ geochemical ref- erence samples, however each element indicates good linear regression relations based on the least squares method. Data of arsenic show relatively low regression relations, however, the values can be used semi-quantitatively only for samples which have low values of lead, such as sediments in Lake Inawashiro-ko. The quantifications of sodium and phosphorus could not be obtained using this method. As a worked example, the non-destructive and sequential SXAM analyses of lacustrine sediments in Lake Inawashiro-ko were performed. Eleven peaks of manganese, iron and sulfur from IN2.5-11 core sample and twelve peaks of iron from IN2.5-11 core sample were identified from the profiles of individual elements. Consequently, these peaks of iron and sulfur profiles can be correlated to the horizons of dark clay layers.%走査型X線分析顕微鏡(SXAM)を用いた非破壊•連続測定による化学組成分析を猪苗代湖湖底堆積物に適用した.そのために，まず岩石標準試料と猪苗代湖湖底堆積物試料を加圧成形した粉末ペレットを用いて，SXAMと蛍光X線分光分析装置(XRF)による定量分析の結果を比較•評価した.SXAMによる岩石標準試料の定量分析は，TiO_2,Al_2O_3,Fe_2O_3,MnO,K_2Oの分析値と推奨値との間に系統的な差はなく，分析値を推奨値に近い値と評価できる.SiO_2,MgO,CaO,SO_3の分析値は，推奨値に対して系統誤差があるが.推奨値との相関は良く.系統誤差の傾向を把握したうえで利用できる.Na_2OとP_2O_5は定量性を得られなかった.Asについては，猪苗代湖湖底堆積物のようにPb含有量が少なく，かつ大きな変化がない場合に相対変動を示す半定量的な値として利用できる.SXAMによる定量分析の各元素の相対誤差は，猪苗代湖湖底堆積物の場合，SiO_2が2%未満,TiO_2が7%未満,AlO_2O_3が5%未満.Fe_2O_3が6%未満,MnOが12%未満，MgOが35%未満，CaOが8%未満，K_2Oが10%未満SO_3が8%未満，Asが35%未満であった.このようにSXAMによる定量分析を評価した上で，猪苗代湖湖底堆積物に対してSXAMによる非破壊•連続化学組成分析を適用し，IN2.5-11コアの厚さ10cm部からFe_2O_3,MnOとSO_3の極大値を11層準.IN2.5-09コアの厚さ12cm部からFe_2O_3の極大値を12層準見いだした.SXAMによるFe_2O_3,MnO,SO_3,As含有量の鉛直変化（プロファイル）は，猪苗代湖湖底堆積物の縞状粘土の明暗部に対応して変化しており，縞状粘土の成因を検討する際の基礎資料となる.