[eli5] If a half-life is the amount of time it takes for a radioactive substance to lose half its radioactivity, and this number is constant no matter how much radiation remains, will there come a time when the substance loses all radioactivity?

Question

[eli5] If a half-life is the amount of time it takes for a radioactive substance to lose half its radioactivity, and this number is constant no matter how much radiation remains, will there come a time when the substance loses all radioactivity?

In: 2

Answer 1

Sort of. First, when we say a “substance loses its radioactivity” remember that we are talking about some radioactive element becoming a different element. That “different element” (the decay product) can also be radioactive and have a completely different half-life.

Speaking strictly in terms of one specific radioactive element, then yes, there will come a time when all atoms of that element have decayed into something else and, if its decay products are also radioactive, a time when it arrives a stable, non-radioactive element.

We just can’t ever say when that will be, which is why we have to use half-lives.