放射性物质由很多不稳定原子构成。
Radioactive materials are composed of atoms that are unstable.
不稳定原子在达到稳定状态前，需要释放出自身多余的能量，这一能量即辐射。
An unstable atom gives off its excess energy until it becomes stable. The energy emitted is radiation.
“这些生物从一个我们从未想到的来源获取能量，”McKay惊叹，“南非的极端微生物细菌吃的是岩石里不稳定原子衰变时的放射能。”
"These creatures get their energy from sources we never imagined," McKay exclaims. "the South African extremophile bacteria are powered by the radioactive decay of unstable atoms in the rocks."
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