Half-Life Notes

1. Half-Life Notes

2. Half-Life: the amount of time it takes half of a radioactive sample to decay. 1 0 ½ ½ ¾ ¼ 1/8 7/8 1/16 15/16 1/32 31/32 1/64 63/64

3. Example 1) Assuming a half-life of 1599 years, how many years will be needed for the decay of 15/16 of a given amount of radium-226? Need 4 half-lives 4 * 1599 years = 6396 years 1 0 0 yrs ½ ½ 1599 yrs ¾ ¼ 3198 yrs 1/8 4797 yrs 7/8 1/16 6396 yrs 15/16

4. Example 2) The half-life of radon-222 is 3.824 days. How much time must past for ¼ of a given amount of radon to remain? Need 2 half-lives 2 * 3.824 days= 7.648 days 1 0 0 days ½ ½ 3.824 days ¾ ¼ 7.648 days

5. Example 3) The half-life of polonium-218 is 3.0min. If you start with 16mg of polonium-218, how much time must pass for only 1.0mg to remain? Starting Amount = 16 mg Remaining Amount = 1.0 mg Fraction Remainig = 1.0/ 16mg = 1/16 1 0 0 min Need 4 half-lives 4* 3.0min = 12 min ½ ½ 3.0 min ¾ ¼ 6.0 min 1/8 9.0 min 7/8 1/16 12 min 15/16

6. After 4797 years, how much of an original 0.250g sample of radium-226 remains? Its half-life is 1599 years.

7. The half-life of radium-224 is 3.66 days. What was the original mass of radium-224 if 0.0800g remains after 7.32 days?