在自然界很稀少，因为它所有的同位素都是短寿命的，还因为它的来源是稀有的。

It is rare in nature because all its isotopes are short-lived and because radium, its source, is scarce.

youdao

在自然界很稀少，因为它所有的同位素都是短寿命的，还因为它的来源是稀有的。

It is rare in nature because all its isotopes are short-lived and because radium, its source, is scarce.

youdao