Isotopes and Radioactive Decay

When an unstable radioactive atom decays, it usually turns into:

• a more stable atom
• a less stable atom
• the exact same atom but with less pure energy
• empty space

Radiometric dating is possible because the rates of decay of radioactive isotopes _____.

• change over time
• change from place to place
• are constant
• vary widely

The time it takes for 50% of the nuclei in a radioactive sample to decay to its stable isotope is called _____.

• the daughter product
• geologic time
• the half-life
• the half-time

According to the graph, what fraction of the original parent isotope still exists after 3 half lives?

• 0.5000 g
• 0.2500 g
• 0.1250 g
• 0.0625 g

You find a rock sample with radioactive atoms present.  If 12.5% of the original radioactive atoms were present, how many half-lives has the rock been around for? (Hint, at Half-Life = 0, you start with 100%)

• zero
• 1
• 2
• 3

You find a rock sample with radioactive atoms present.  If 25% of the original radioactive atoms were present, how many half-lives has the rock been around for? (Hint, at Half-Life = 0, you start with 100%)

• zero
• 1
• 2
• 3

If the half-life of a radioactive group of atoms is 100 years, then how old is the rock if there have been two half-lives?

• 25 years
• 200 years
• 400 years
• 800 years

Suppose you found a material in which 12.5% of the original radioactive atoms were still present.  If the half-life of an atom is 60 years, how old is the material?

• 30 years old
• 60 years old
• 120 years old
• 180 years old

If the  half-life of a radioactive group of atoms is 100 years, then how old is the rock if there have been ten half-lives?

• 10 years
• 100 years
• 1000 years
• 10000 years

The table shows the radioactive decay of carbon-14. Part of the table has been left blank. 
After THREE half-lives have passed, approximately what percentage of the original carbon-14 remains? 

• 25%
• 12.5%
• 6.25%
• 3.125%