## Question

What is the half life of plutonium?

## Answer

Eric - The half life of plutonium 239 is 2.4 x 10 4 years. The other isotopes of plutonium have a little bit shorter half life than that. Dave - So that means that if you're breaking plutonium down into something which has a half-life of only 300 years, that's definitely improving the radioactive danger and pollution problem. Eric - Yes. If you look at the repositories they grapple with, these long term elements, and I call them transuranic, those elements above uranium, where they have half lifes of hundreds of thousands of years, that makes it tough on a repository design. If you get down to where you have fission products which are on hundreds of years then your repository design can be, I think, simpler and a little bit different. Ben - And just to clear up a couple of the basics of things, half life essentially means that after that many years, you will have half as much of the original product. So it doesn't mean that it will only last twice that length because after that many years again, you have half again. Eric - Right, but just to be clear for your listeners, if I have 1 kg of plutonium, If I come back after 1 half life, I'll have Ã?,½ kg of plutonium and Ã?,½ kg of uranium because plutonium decays into uranium.

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