Its air has been so radioactive, a worker could be exposed only five hours before exceeding a safe limit.

安全壳内的空气具有相当的辐射性，工作人员最多只能曝露5个小时，否则就超过安全范围。

youdao

They had been interested in thorium -- a radioactive element that can fuel nuclear reactors but not be processed into weapons.

VOA: special.2010.10.15

Suppose we've got some sort of radioactive atom, which has a certain chance of decaying.

假定我们有某种放射性原子,它们以一定的几率衰变

耶鲁公开课 - 死亡课程节选

4 And then there are the last four, carbon 14, which is a radioactive form.

然后，还有碳，以放射性形式存在。

麻省理工公开课 - 固态化学导论课程节选

Radioactive decay happens when a radioactive substance emits a particle.

FORBES: Radioactive Decay Rates May Not Be Constant After All

To call Rangers a poisoned chalice is a bit like calling a mug of radioactive chemicals a nice cup of coffee.

FORBES: What Can We Learn From the Financial Meltdown of Glasgow Rangers FC?

And what if the waste produced by such a reactor was radioactive for a mere few hundred years rather than tens of thousands?

FORBES: Is Thorium the Biggest Energy Breakthrough Since Fire? Possibly.