1. H ALF L IFE P RACTICE

2. Y OU HAVE 5 G OF SODIUM 25. H OW MUCH WOULD YOU HAVE AFTER 3 HALF LIVES ? Step 1: 25  12.5  6.25 6.25g remain

3. Now You

4. C14 HAS A HALF LIFE OF 5730 YEARS. I F YOU HAD 88 G, HOW MUCH C14 WOULD REMAIN AFTER 5 HALF LIVES ? Step 1: 88  44  22  11  5.5  2.75g

6. A CTINIUM 226 HAS A HALF LIFE OF 28 HOURS. 100 G OF ACTINIUM 226 DEGRADES OVER 56 HOURS. H OW MUCH WILL BE LEFT ? Step 1: 56/28=2 Step 2: 100g  50g  25g 25g

7. Now You

8. A FTER 11,200 YEARS, A SAMPLE OF RADIUM -226 HAS DECAYED. I T HAS A HALF - LIFE OF 1600 YEARS. T HE SAMPLE WAS ORIGINALLY 162 GRAMS. H OW MUCH IS LEFT ? Step 1: 11,200/1600=7 Step 2: 162  81  40.5  20.25  10.125  5.0625  2.53125 2.53125g

10. T HE HALF LIFE OF ISOTOPE X IS 2 YEARS. H OW LONG WOULD IT TAKE FOR 4 G TO DECAY TO.5 G ? Step 1: 4  2  1 .5 (3 Half lives have passed) Step 2: 3X2years=6 years

11. N OW Y OU

12. C ARBON HAS A HALF LIFE OF 5730 YEARS. H OW LONG WOULD IT TAKE 100 G TO DECAY TO 25 GRAMS ? Step 1: 100  50  25 (2 half lives have passed) Step 2: 5730 years X 2=11460 Years

14. A SAMPLE INITIALLY CONTAINS 60 G OF THORIUM 234. A FTER 48 DAYS ONLY 7.5 GRAMS REMAIN. H OW LONG IS ONE HALF LIFE ? Step 1: 60  30  15  7.5 (3 half lives have passed) Step2: 48/3=16 16 days

15. Now You

16. W E START WITH 500 G OF ISOTOPE X. I N 10,000 YEARS WE END WITH 7.8 G. H OW LING IS ONE HALF LIFE FOR ISOTOPE X? Step 1: 500  250  125  62.5  31.25  15.6  7.8 (6 half lives have passed) Step 2: 10,000/6 = 1666.66 One half life is 1666.66 years