Half-Life

Each atom decays at a fixed time.

All atoms decay simultaneously.

Individual atoms decay randomly, but large groups decay predictably.

Decay only happens in certain elements.

Uranium-238

Carbon-14

Polonium-214

Nitrogen-14

Half-life is the time it takes for all of a sample to decay.

Half-life is the time it takes for half of a sample to decay.

Half-life is the time it takes for a sample to double in size.

Half-life is unrelated to radioactive decay.

3 years

6 years

8 years

12 years

Dating ancient rocks

Dating once-living things up to about 50,000 years old

Measuring radiation at nuclear sites

Determining the age of the universe

It helps scientists predict the weather

It allows scientists to date ancient artifacts and fossils

It is used to create new elements

It helps scientists grow plants faster

After 2 half-lives, 50% of the original sample remains.

Carbon-14 dating is effective for biological samples up to about 50,000 years old.

If uranium-238 has a half-life of 4.5 billion years, then after 9 billion years, about 25% of the original sample would remain.

A fossil with 12.5% of its original carbon-14 has undergone three half-lives and is approximately 17,190 years old.

All isotopes decay at the same rate

Radioactivity means instant danger

Half-life means half the time to disappear

Longer half-life means slower decay and lower radioactivity

1 Half-life

2 Half-lives

3 Half-lives

4 Half-lives