Chronological analysis of Omura Bay bottom sediment by measurement of environmental radioactivity

分析了大村湾底部的沉积物。用锗半导体探测器对放射性进行了分析。采用电感耦合等离子体原子发射光谱法（ICP-AES）对主要元素进行了分析。微量元素的分析主要采用电感耦合等离子体质谱法（ICP-MS）。根据Pb-210的放射性，对水平分离的沉积物岩心样品进行了测年。沿岸的沉积速率往往比海湾中部快。这一趋势与直教湾和大阪湾相同。铯-137的垂直分布没有显示出核试验全球沉降物的明显峰值，用铯-137的分布进行测年是困难的。主元素P、Ti、K、Mg、Na、Al和Ca的垂直和水平分布基本均匀。K、Ti、Y、Rb、Sr、Zr、Nb、Cs、Hf、Th、Na、Zn、W、Pb和Cd的浓度高于地壳平均浓度。元素中Na、Zn、W、Pb、Cd的浓度呈上升趋势。Cu的浓度也明显升高。不能轻易下结论说流入海湾的微量元素随着年份的增加而增加，因为这些元素可能会液化到地表。而在缺氧条件下易液化的Fe和Mn的浓度则呈下降趋势。在向上增加的元素中，Cd是一个重要的环境因子，如果它越来越多地涌入海湾，可能是人类活动造成的，结果非常值得注意。

Sediments at the bottom of the Omura bay was analyzed. The radioactivity was analyzed by a Germanium semiconductor detector. The principal elements were analyzed by the inductively coupled, plasma atomic emission spectrometry (ICP-AES). The trace elements were mainly analyzed by the inductively coupled plasma mass spectrometry (ICP-MS).From the radioactivity of Pb-210, horizontally separated core samples of the sediments were dated. The sedimentation rate along the coast tends to be faster than the middle of the bay. The tendency is same as Zbkyo bay and Osaka bay. The vertical distribution of Cs-137 did not show clear peak of the Global fallout of the nuclear tests and the dating with Cs-137 distribution was difficult.The distributions of the principal elements, P, Ti, K, Mg, Na, Al, and Ca were almost uniform vertically and horizontally. The concentration of K, Ti, Y, Rb, Sr, Zr, Nb, Cs, Hf, Th, Na, Zn, W, Pb and Cd was higher than the average concentration of the earth's crust. In the elements, concentration of Na, Zn, W, Pb and Cd were increasing upward. The concentration of Cu was also clearly increasing upward. It is not appropriate to conclude easily that these trace elements pouring into the bay increase with the years because these elements may liquate out up to the surface. But concentration of Fe and Mn, which is known to liquate in anoxic condition, was decreasing upword oppositely. In the elements increasing upward, Cd is an important environmental factor, and if it is increasingly pouring into the bay, it may be the sake of human activity, and very noteworthy result.