RADIOACTIVITY EXERCISE SHEET

1.    You start out with 10,000 atoms of an unstable, radioactive isotope.

        After 1 half life, how many parent atoms are there?

After one half life, half of the parent atoms have decayed.  Therefore there are 5,000 parent atoms.

        How many daughter atoms are there?

10,000 - 5,000 = 5,000 daughter atoms

       After 2 half lives, how many parent and how many daughter atoms are there?

After 2 half lives, one half of the remaining parent material has decayed to daughter product so there are 2,500 parent atoms and 7,500 daughter atoms.

After 3 half lives, how many parent and daughter atoms are there?

After 3 half lives, one half of the remaining parent material has decayed to daughter product so there are 1,250 parent atoms, and 8,750 daughter atoms.

2.    You find that the ratio of parent: daughter atoms is 500:500.

        a.    How many half lives have passed?

If the ratio is 1:1, then 1 half life has passed.

        b.     If the ratio is 1250:8750 how many half lives have passed?

If the ratio is 1:7, then 3 half lives have passed.

        c.    If the length of a half life is 5700 years, how old are the samples in a and
               b above?

If 1 half life has passed, then the age of the object is 5700 years. (1 X 5700 years = 5700 years)

If 3 half lives have passed, then the age of the object is 5700 years/half life X 3 half lives = 17,100 years.