Half-Life Answers

   1. What is a becquerel?

  One decay per second

   2. What is the half-life of a radioactive isotope?

  The time that it takes for half of the parent nuclei to decay

   3. A substance has a half-life of 3 hours. 
What fraction of the atoms will have decayed after 6 hours?

  3/4 of the atoms will have decayed 

   4. A radioactive substance activity falls from 8,000 counts per minute to 500 counts per minute in 20 hours. What is the half-life of the substance?

  5 hours

   5. After the 3rd half-life, how much of the sample is left?

  25%  |  11/4  |  0.25

   6. After the second half-life, how much of the sample is left?

  50%  |  1/2  |  0.5

   7.  What does the beta particle have a charge of?

  Minus 1

   8.  If Carbon-14 has a half-life of 5,730 years, how old is a fossil if it has undergone 4 half-lives?

 22,920 years old

   9.  If Carbon-12 has a half-life of 5,730 years, how old is a fossil if it has undergone 7 half-lives?

  40,110 years old

   10. An isotope has a half-life of 6 hours, what percentage of the isotope will be left after 24 hours?

  6.25%