Radioactive Decay

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

Some atoms in the parent are isotopes These atoms have a different number of neutrons than protons They are unstable As isotopes decay to stable daughter energy is released

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

… or when ...

But one thing we do know...

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

Radioactive Decay Parent – unstable Daughter – stable Half-life is the time required for HALF of the atoms of the unstable parent to decay to stable daughter

Radioactive Decay Data Parent Daughter Half-live years Carbon 14 Nitrogen 14 5,700 Potassium 40 Argon 40 Calcium 40 1.3 billion Uranium 238 Lead 206 4.5 billion Rubidium 87 Strontium 87 49 billion

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

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

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

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

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

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

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.)

Shape of curve similar for each radioactive isotope

Half Life Continues indefinitely Random and spontaneous Not affected by temperature or pressure Not affected by mass or volume of parent