1. Radioactive Decay

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

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

5. … or when ...

6. But one thing we do know...

7. ...is that it always takes the same
amount of time for half to disappear.
(8 atoms)

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

19. One half-life.

20. Two half-lives.

21. Three half-lives.

22. Four half-lives.

23. Don’t worry about the last atom
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.)

24. 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% parent
0% daughter
0 half lives

25. One half-life.
50% parent
50% daughter
1 half-life

26. Two half-lives.
25% parent
75% daughter
2 half-lives

27. Three half-lives.
12.5% parent
87.5% daughter
3 half-lives

28. Four half-lives.
6.25% parent
93.75% daughter
4 half-lives