Radioactivity

[Birt]

Sorry guys, im in a bit of a science mood today. What does Half life mean exactly.
Does a radioactive element eventually disappear once all its radioactive decay has taken place?
It confuses me why, for instace Pl decays to another element. If anyone can explain this to me in fairly plain english i would be grateful.

[Top_Gooner]

The half-life of a quantity subject to exponential decay is the time required for the quantity to decay to half of its initial value. The concept originated in the study of radioactive decay, but applies to many other fields as well, including phenomena which are described by non-exponential decays.

from wikipedia

[Loosehead]

It's explained quite well here:
http://www.colorado.edu/physics/2000/index.pl

[ugly_bob]

The element doesn't disappear.
The half life is regarding the radioactivity of the element. So for example if substance A had a half life of 5 minutes, and at time 0 was emitting 20 units of radiation per second, after 5 minutes, it would be emitting 10 units, after 10 minutes, 5 units etc.
What usually happens is that the element decays into another, ore stable, form of that element (eg from uranium 238 to Uranium 232) <- numbers may be wrong, can't remember.