Nuclear plants use Plutonium-239, which has a chemical half-life of 24, 000 years, meaning anything leaked from Fukushima today will still affect the area for thousands of years to come.
Nuclear fission can only occur in some types of heavy and unstable nuclei such as in the uranium -235 and plutonium -239.
核裂变只能在某种类型的重核及不稳定核素内发生，如铀- 235及钚- 239。
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On the other hand, analyses of 85 Kr, a fission product of uranium-235 and plutonium-239, can serve as a means to help verify compliance with the Nuclear Non-Proliferation Treaty.