What is the reason radioactive decay is measured in half-life’s instead of just using the elements “full-life”?

Question

Is there something special about the halfway point? Does the decay happen at a steady pace or exponentially?

In: 910

Answer 1

Explanations of half-life on the thread are excellent. There actually is a case where we consider “full life”, at least sort of. For nuclear medicine purposes, we consider a radioactive material no longer physiologically relevant after 10 half-lives, so that can be considered the “full life” biologically speaking. For instance, iodine 131, used to treat overactive thyroid and some types of thyroid cancers, has a half-life of 8 days. After 80 days, or 10 half-lives, there’s simply not enough radioactivity left to be effectively bombarding cancer cells. (There’s also the biological half-life, which is the body eliminating the foreign material, but that’s outside of ELI5 considerations.)