• Question: Why is radioactive decay random and spontaneous?

    Asked by freddie to Adam, Geoff, Rob, Sheila, Suzie on 18 Mar 2011 in Categories: .
    • Photo: Adam Tuff

      Adam Tuff answered on 17 Mar 2011:

      Like most things governed by Quantum mechanics, it’s random because it is! The best way I can invision the decay is by putting a little steel ball inside of a pingpong ball, and put a hole in the side of the ping pong ball just big enough for it to get out – shake the ping pong ball and timing how long it takes the little steel ball could mean you see it come out of the hole in a few seconds, or it could mean it will never come out of the hole. I like to think of that as a good analogy for particle emission, although the hole is metaphorical. This is slightly away from your question, as in a sense it’s not possible to have a “proof of randomness” in any sense. Great question!

    • Photo: Suzie Sheehy

      Suzie Sheehy answered on 18 Mar 2011:

      That’s a great question! And a particularly tough one, I’d have to say. Radioactive decay can be ‘triggered’ by either an event in the nucleus and occasionally by an electron getting involved.
      It is a random or ‘stochastic’ process (that’s Greek for random, but we use the word a lot) and the reason it’s random has to do with quantum mechanics.
      Radioactive decay happens when a particle ‘quantum tunnels’ into or out of the nucleus. This has to be random – because of quantum mechanics everything is ‘fuzzy’ at that level and everything is a statistical process, rather than a predictable one.

    • Photo: Sheila Kanani

      Sheila Kanani answered on 18 Mar 2011:

      Great question, as I don’t think we really know the answer, but we have a few good guesses.

      Radioactive decay involves the spontaneous transformation of one element into another. The only way that this can happen is by changing the number of protons in the nucleus. There are a number of ways that this can happen and when it does, the atom is forever changed. There is no going back!

      This is very much like popping popcorn, there is no way to know which will pop first. And once that first kernel pops, it will never be a kernel again…it is forever changed!

      The reason atoms spontaneously throw off a particle is because the atom is unstable and it is trying to make itself stable.

      If you were looking at an individual atom, it would be impossible to predict when it would throw off a particle. However, if you have a large collection of the same atoms, then the rate of decay becomes quite predictable.