1. Radioactive Decay

2. I can solve half-life problems. Radioisotopes decay in a predictable way – The time is takes for half of a sample to decay is called the half life for the isotope. – Every radioactive element has a unique half-life C-14 is 5730 years U-238 is 4.5 billion years I-131 is 8.05 days

3. I can solve half-life problems Barium-122 has a half life of 2 minutes. A fresh sample weighing 80 g was obtained. If it takes 10 minutes to set up the experiment using barium-122, how much barium-122 will be left when the experiment begins TIMEStart2 min4 min6 min8 min10 min Mass80 g

4. I can solve half-life problems 1.How many half-lives have passed when 25% of parent isotope remains? 2.What percent of the parent isotope remains after 5 half-lives? 3.If we started with 200 grams of a radioisotope, how much would be left after 2 half-lives?

5. I can solve half – life problems 1.What is the half-life of strontium-90? How do you know? 2.How many half-lives have passed when 12.5 grams of Sr-90 remain? 3.How much Sr-90 remains after 8 half-lives?

6. I can solve half-life problems Use the formula – The amount remaining is equal to the original amount times 1/2 raised to the # of half-lives that have passed. N=N 0 (1/2) n N= amount of remaining radioisotope N 0 = original amount of radioisotope sample n= # of half lives that have passed (time elapsed/half life)

7. I can solve half-life problems Barium-122 has a half life of 2 minutes. A fresh sample weighing 80 g was obtained. If it takes 10 minutes to set up the experiment using barium-122, how much barium-122 will be left when the experiment begins N=N 0 (1/2) n – N=? – N 0 =80g – n= time elapsed/half life = 10 days/2 days = 5 N= 80g (1/2) 5 N=80g (1/2)(1/2)(1/2)(1/2)(1/2) N= 2.5 grams Barium-122

8. I can solve half-life problems Actinium-226 has a half-life of 29 hours. If 100 mg of actinium-226 decays over a period of 58 hours, how much actinium-226 will remain? N=N 0 (1/2) n N=? N 0 =100 mg Ac n= 58 days/29 days= 2 half lives pass N= 100 mg (1/2) 2 N=25 g Ac

9. I can solve half-life problems Iodine-131 is used to destroy thyroid tissue in the treatment of an overactive thyroid. The half-life of iodine-131 is 8 days. If a hospital receives a shipment of 200 g of iodine-131, how much I-131 would remain after 32 days? N=N 0 (1/2) n N=? N 0 =200 g I n= 32 days/8 days= 4 half lives N= 200g (1/2) 4 N= 12.5 g I

10. I can solve half-life problems Mercury -197 is used for kidney scans and has a half-life of 3 days. If the amount of mercury-197 needed for a study is 1.0 gram and the time allowed for shipment is 15 days, how much mercury-197 will need to be ordered? N=1.0 grams Hg-197 N 0 = ? n=15 days/3 days= 5 half lives 1.0grams= N 0 (1/2) 5 N 0 =32 grams