Can someone explain the radioactive decay of that would happen over time to a 1 cubic decimeter block of plutonium?

Question

I just saw an article talking about naturally occurring plutonium on Earth and it said that some [or many or some other purposefully ambiguous statement] people think this element could [another good weasler to not commit to an answer in case you're wrong] be primordial. So, I started thinking. How long could plutonium last? As far as I know, nothing alters radioactive decay, right? So, no matter if it were in the Earth's bowels, hit by an asteroid, then a couple nukes, etc., the decay rate remains unaltered, right? So, I wanted to see a detailed breakdown of what percent of the cube would be element/isotope (x) at time (p); while the rest of the cube is element/isotope (y) at time (p) all the way until the cube becomes stable. I know the example may sound misleading but I don't really want the answer in equations and whatnot. This is all for my little curiosity and don't really care if you're off by a little. It would be awesome if you could this for Pu 244; Pu 247; and then whichever isotope would undergo the most radical change (I am sure that is based in opinion). Make whatever assumptions you need, just make sure you say, in your answer [obviously, on a side note f*** OCD], what assumptions you made. Thanks

Answer 1

I thought I'd post the article - never a bad idea. (If it's not the article, let me know).

http://www.scientificamerican.com/article/do-transuranic-elements-s/

I'm going to give a long answer, cause I think I see what you're going for, having read a few of your questions. Also, I appreciate your questions, I found them interesting.

What this article suggests is that when a U-238 shoots out a Neutron, sometimes that Neutron hits another U-238 which leads to a P-239. It's naturally (but rarely) occurring, created by radioactive decay in one molecule, affecting a nearby molecule.

or - how the article explains it:

The isotope Pu-239 was produced on March 28, 1941 by bombarding a U-238 target with neutrons to produce U-239 (half-life of 23.5 minutes). This radionuclide decayed by beta emission to Np-239 (half-life of 2.12 days), which subsequently decayed by beta emission to Pu-239 (which has a very long half-life of 24,600 years).

Plutonium is produced in nature through the reasonably well-understood process discussed above. Uranium is a naturally occurring element that is ubiquitous in the Earth's crust. The isotopes of uranium decay primarily by alpha-particle emission, but there is also a process called "spontaneous fission" that occasionally competes with alpha decay.

In spontaneous fission, the nucleus splits ("fissions") and additional neutrons are released. There is a possibility that these released neutrons are absorbed (captured) by another U-238 nucleus. If this occurs, it triggers a process that produces Pu-239 in a manner similar to that discussed above. Thus, we have plutonium produced naturally in the environment (admittedly in trace quantities). This reaction has been going on since the creation of the Earth.

So, you wrote:

I just saw an article talking about naturally occurring plutonium on Earth and it said that some people think this element could be primordial.

Now, as to the element being primordial (existing at the birth of the solar system), That's more difficult to prove. It's hard to prove that an element with a half life of 264,000 years was around 4 billion years ago. Any Pu-239 that was around when the earth formed would be long gone.

So, no matter if it were in the Earth's bowels, hit by an asteroid, then a couple nukes, etc., the decay rate remains unaltered, right?

Yes, as far as I know this is true.

So, I wanted to see a detailed breakdown of what percent of the cube would be element/isotope (x) at time (p); while the rest of the cube is element/isotope (y) at time (p) all the way until the cube becomes stable.

The math is pretty simple. A half life of 264,000 years means the element is half gone in 264,000 years, only 1/4 remains after 528,000, 1/8th after 792,000 and roughly 1/16th after a bit over a million years - and each million years after, it's a 1/16th of what remains, so 4 million years, 1/16th of 1/16th of 1/16th of 1/16th - or one about 1/30,000. 8 million years, 1/900,000,000 - at which point, we're nearing the point where it's no longer detectible. 4.5 billion years - forgedabout it.

You need a very long half life (U238 for example) for an element to still be around from the formation of the solar system. Anything with a half life much less than, say, 50 million years is very hard to detect as "Primordial" because there would be so little of it left. That's why Pu239 is naturally occurring on earth (an occasional product of U238), but Pu241 and Pu244 are gone.

Also, not strictly related to your question but if you have a block of pure plutonium, that changes the half-life equation, because as one nuclei decays it would bombard neighboring elements, that speeds up the decay rate.

The article mentions Pu 244 and Pu 241. (not 247) You can look up all the half lives in Wiki. PU 244 is the most stable. http://en.wikipedia.org/wiki/Isotopes_of_plutonium

All the Pu Isotopes are likely formed in stars during the r-Process

http://en.wikipedia.org/wiki/R-process

Not sure that helps, but I gave it my best shot.

More details in this answer: Age of the Earth and the star that preceded the Sun