Radioactivity half-life half longer unique has a t½ = 3 min 50% 25% One way that scientists measure radioactivity is in terms of an isotope’s _________, which is the amount of time it takes for ________ of the nuclei to decay into a new element. The more stable an isotope is the __________its half-life. Every isotope has a ___________ half-life. For example, ____________________. In those three minutes, half of the original sample will decay so that _____ of the original material remains. In 6.0 minutes, two half-lives will pass and _____ of the original sample will remain. Depending on the __________, __________, and ________ of exposure some radiation is very dangerous, while others are very useful to humans. half-life half longer unique has a t½ = 3 min 50% 25% source type amount

Half-life Graphs

Half-life Graphs

Half-life Graphs

Uses and Risks of Radiation Length of t½ the Half-life Uses and Risks of Radioactive Isotopes Isotope Uses and Risks of Radiation Length of t½ the Half-life 4.5 billion yr Find the age of very old rocks 5730 yr Find the age of previously living things Destroy cancer cells 5.27 yrs Treat thyroid disorder 8 days Tracer used just to identify cancer cells 6 hours

Sample Problem: Half-life has a t½ = 5.27 years. What percentage of the original sample would be left after 21.08 years? What mass would be left after 21.08 years if the original sample weighed 160 grams? 100.00% 50.00% 25.00% 12.50% 6.25% Orignal 160 g 80 g 40 g 20 g 10 g 21.08 yr 1t1/2 ----------- 5.27 yr = 4 half-lives 2t1/2 3t1/2 4t1/2

10 9 8 7 6 5 4 3 2 1 10/17 Radioactive Decay & Half-life Leave H#10 out to be checked Examine the 10th grade Candyium Lab Data Tape the graph into your notebook. Create a bar graph for the radioactive decay over 12 hr for an isotope that starts with 8000 atoms and has a half-life of 2 hr. # of atoms

10/17 Radioactive Decay & Half-life Create a bar graph for the radioactive decay over 12 hr for an isotope that starts with 8000 atoms and has a half-life of 2 hours. 8000 = 0 t½ = 100% 1 t½ = 4000 = 50% 2 t½ = 2000 = 25% 3 t½ = 1000 = 12.5% 4 t½ = 500 = 6.25%

Sample Problem: Half-life