Radioactive Isotopes and "Half-Lives"

The half-life of uranium-238 is approximately...

4.5 billion years.

The half-life of an isotope depends on...

the stability of the isotope.

If an isotope has a long half-life, it is most likely...

relatively stable.

If an isotope has a short half-life, it is most likely...

relatively less stable.

True or false: Half-lives can range from seconds to billions of years.

True

It takes 60 hours for a 208-gram sample of sodium-24 to decay to 13 grams. What is the half-life of sodium-24?

15 hours

A radioactive isotope has a half-life of 8.1 days. If you start with 50 grams, how long will it take until only 6.25 grams remain?

3 days

24.3 days

If a 100-gram sample of nitrogen-16 decays to 12.5 grams of nitrogen-16, how many half-lives have passed?

3 half-lives

Radioactive decay happens when you have...

an unstable nucleus.

What isotope is formed when uranium-238 goes through alpha decay?

Thorium-234

Half-life measures...

how long it takes for half of a sample to decay.

A radioactive substance has a half-life of 250 years. If only 50 grams of the sample remain, how much of the substance was there 1,500 years ago?

3,200 grams

Which of the following can be dated using carbon dating?

A fossil estimated to be 7,500 years old

You have 4 grams of a radioactive sample that has a half-life of 2 days. How much would you expect to remain after 10 days?

0.125 grams