氦是钍和铀元素数千年放射性衰变的副产品。
Helium is the by product of millennia of radioactive decay from the elements thorium and uranium.
这颗晕星不同于大多数超新星，它吐出的许多元素比铁还重，其中包括放射性钍和铀。
Unlike most supernovae, this one spewed lots of elements far heavier than iron, including radioactive thorium and uranium.
他们当时对一种放射性元素钍很感兴趣，这种元素能驱动核反应堆，却不能制造生产成武器。
They had been interested in thorium — a radioactive element that can fuel nuclear reactors but not be processed into weapons.
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