All are radioactive and have similar properties to actinium.
这些元素都有放射性，而且性质与锕相似。
There are three naturally occurring radioactive series - the thorium series, the actinium series, and the uranium series.
有三个天然存在的放射系列，即钍系、锕系和铀系。
There are three naturally occurring radioactive series - the thorium series, the actinium series, and the uranium series.
有三个天然存在的放射系列，即钍系、锕系和铀系。
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