actinium
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        A soft,silvery-white,highly ra-dioactive metallic element of group 3 (for-merly ⅢB) of the periodic table. It is usual-ly considered to be the first member of theACTINOID series. It occurs in minute quan-tities in uranium ores as a result of the natu-ral ......（本文共 842 字）     [閱讀本文] >>