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

对大村湾底部的沉积物进行了分析。用锗半导体探测器进行放射性分析。采用电感耦合等离子体原子发射光谱仪(ICPAES)对样品中的主要元素进行分析。采用电感耦合等离子体质谱(ICPMS)对沉积物中的微量元素进行了分析，根据铅-210的放射性，确定了沉积物中水平分离的岩心样品的年代。海岸的沉积速率往往比海湾中部的沉积速率快。这一趋势与Zbkyo湾和大阪湾相同。~(137)Cs垂直分布没有显示出明显的全球放射性尘埃峰值，用~(137)Cs分布测年困难，主量元素P、Ti、K、Mg、Na、Al、Ca在垂直和水平方向上分布基本均匀。K、Ti、Y、Rb、Sr、Zr、Nb、Cs、Hf、Th、Na、Zn、W、Pb、Cd等元素的含量高于地壳平均含量。元素中，钠、锌、钨、铅、镉的含量呈上升趋势。铜的浓度也有明显的上升趋势。不能轻易地得出这样的结论，即这些进入海湾的微量元素随着时间的推移而增加，因为这些元素可能会熔化到表层。而已知在缺氧条件下熔融的铁和锰的浓度则相反地下降。在向上增加的元素中，Cd是一个重要的环境因素，如果它越来越多地涌入海湾，那可能是出于人类活动的原因，而且结果非常值得注意。

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.