Radioactive Decay

Radioactive materials decay from the “Parent” material into the “Daughter Product”.

Original“Parent” Material

Daughter Product

You’ll never know which atoms will decay...

(16 atoms)

… or when ...

But one thing we do know...

...is that it always takes the same amount of time for half to disappear.

(8 atoms)

Each half-life, the amount of atoms gets cut in half.

One half-life.

Two half-lives.

Three half-lives.

Four half-lives.

Don’t worry about the last atom. You start with so many trillions that

you never really get there. (It will just decay and then

they’re all gone.)

Since you don’t know how many atoms you started with, a ratio between parent to daughter will tell you how many half-

lives have gone by.

100% parent0% daughter0 half lives

One half-life.

50% parent50% daughter1 half-life

Two half-lives.

25% parent75% daughter2 half-lives

Three half-lives.

12.5% parent87.5% daughter3 half-lives

Four half-lives.

6.25% parent93.75% daughter4 half-lives