1. 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

2. Half-life Graphs

3. Half-life Graphs

4. Half-life Graphs

7. 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

9. Sample Problem: Half-life
has a t½ = 5.27 years. What percentage of the original sample would be left after years? What mass would be left after 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

11. 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

12. 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%

14. Sample Problem: Half-life