On Wed, 23 Sep 2009 22:57:12 +0100, Paul Martin wrote:

If you start with a finite number of radioactive atoms you'll
halve the
number every half-life period

On average. Sometimes it will, sometimes it won't. It's random.

, at some point there'll be one atom left and when that decays it's
all gone.

On average. Maybe. It's random.

Quite. If the half life is say 1 year after 1 year there is a 50%
*probabilty* that the lone atom might have decayed. Even after
hundreds of years you can't say that that lone atom *will* have
decayed just that the probabilty of it happening is pretty high(*)
but you can't say when it will happen.

(*) I think, what does happen to the probabilty of an event after N
half lives? Gut feeling is that the probabilty increases but as for
any given half life period it's stuck at 50% I'm not so sure.

--
Cheers
Dave.