Science Questions

What is the half life of plutonium?

Tue, 27th Mar 2012

Listen Now    Download as mp3 from the show Nuclear: About to Explode?


Eddie in Northampton asked:

What is the half life of plutonium?


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 doesnít 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, Iíll have Ĺ kg of plutonium and Ĺ kg of uranium because plutonium decays into uranium.


Subscribe Free

Related Content


Make a comment

I do not have the figures to hand but some isotopes of Plutonium have a very short half life making them a useful source of heat in thermo electric generators syhprum, Fri, 30th Mar 2012

From wikipedia: damocles, Sat, 31st Mar 2012

Here is a list of the half-lives of all the known Plutonium isotopes.  Some decay in less than a second.  Others decay over thousands of years.  Of course, Fission is a different process in which the atoms break apart, occurring much quicker. 

Plutonium-238 (238Pu) is used for Thermal Electric Generators, and has a half-life of 87.7 years.  Thus, the Voyager probes have probably used up about 1/4 of their original Plutonium by now.  In this case, the 238Pu decays to 234U with a half-life of 246,000 years, which then decays to 230Th, also with a long half-life of 75,380  years, and so-on. 

So, while the deep space probes will loose most of their Plutonium in a few centuries, they will remain radioactive for millions of years.

The overall proportion of decay products, depends on the half-life of each decay product.
239Pu (half-life 24,200 years) --> 235U (half-life 700 million years, so it will build up as a decay product) --> 231Th (half-life 25.5 hours, so it will not significantly build up) --> 231Pa (half-life of 32,760 years, a little remains, but much shorter half-life than the 235U) --> 227Ac(half-life, 21 years) --> 227Th (as well as some 223Fr)  (For 227Th, 18 days, no build-up) ---> 223Ra (11 days) -> 219Rn (3 seconds)  --> 215Po (2 ms) --> 211Pb (36 min) --> 211Bi (2 min) --> 207Tl (4 min) --> 207Pb (stable form of lead). CliffordK, Sat, 31st Mar 2012

See the whole discussion | Make a comment

Not working please enable javascript
Powered by UKfast
Genetics Society