1. Half life

2. Half Life
Half life is the amount of time required for half of the substance to decay
Example 1:
The half life of Polonium-214 is 1 sec. If you have 10 grams of Po-214, how much will you have after one half life?
Solution: After one half life(1 sec) you will have half of the original amount(10 grams) so after 1 sec you will have 5 grams

3. Half Life
Example 2:
The half life of Polonium-214 is 1 sec. If you have 10 grams of Po-214, how much will you have after two half lives (2sec)?
Solution: After one half life(1 sec) you will have half of the original amount(10 grams) so after 1 sec you will have 5 grams. After two half lives(2sec) you would have 2.5 grams

4. Half Life
Example 3:
If As-81 has a half life of 30 seconds and you have 20g of As-81, how long will it take for there to be 10g?
Solution: 10g is half of 20g so it takes one half life for there to be 10g which is 30seconds.

5. Half Life Practice write answers on a separate sheet
How long does it take a 100g sample of As-81 to decay to 50g if the half life is 30sec?
How long does it take for an 18g sample Na-24 to decay to 4.5g if the half life is 15 hours?
A 30g sample of Ar-35 decays to 15g in 6 seconds, what is the half life of Ar-35?
Challenge! After 40 days a 20g same of P-32 contains only 5g. What is the half life of P-32?

6. Half Life Practice answers
30sec
30 hours
6 seconds
Challenge! 20 days

7. Complete the half life worksheet you received last week; if you can’t find it, click here then click on the Jan link