In message o.uk, Dave
Liquorice writes
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.

IIRC the original assertion was that the radiation would never fall to
zero. If there's just one atom left and it doesn't decay then it
releases no radiation. Once that last atom has decayed there's also no
radiation.



--
bof at bof dot me dot uk