Radioactive Decay
Life Science: Natural World
What does DECAY mean?
Rotting
Death
Changing from one thing to another
ISOTOPE
Atoms of the same element have a different number
of neutrons
Carbon
Carbon 12 and Carbon 14
Carbon 12 is MUCH MORE STABLE than Carbon 14
How can carbon become stable?
Radioactive Decay
How Isotopes Help Us
We can measure the amount of a radioactive element
to determine the age of a fossil
Each element has a HALF LIFE
The amount of time it takes for HALF of the material to
decay (turn into a stable element)
Half Life
We can figure out how much time has passed
We can figure out how much of an remains
Needed information:
The time for one half life
The amount of the material (starting and ending)
How much time has passed
Things to Check For:
If you find it, underline it
 Starting material amount
 Ending material amount
 Total time
 Number of half lives
 Time for one half life
Circle what you are solving for
Practice with Cougartonium
Cougartonium has a half life of 4 years.
If an artifact started out with 10 grams of
Cougartonium and 4 years have passed, how much of
the Cougartonium remains?
Underline the important information
Practice with Cougartonium
Cougartonium has a half life of 4 years.
If an artifact started out with 10 grams of
Cougartonium and 4 years have passed,
how much of the Cougartonium remains?
The Solution
Starting Material Number of Half
Lives
10 grams
??
Years Passed
4 years
Ending Material
??
Since we know that one half life is 4 years, we know how many half lives
have occurred.
The Solution
Starting Material Number of Half
Lives
10 grams
1
Years Passed
4 years
Ending Material
??
The Solution
Starting Material Number of Half
Lives
10 grams
1
Years Passed
4 years
Ending Material
??
Since we know know how many half lives (1) and how much starting
materials (10 grams), we can divide 10 grams by 2 (or multiply by ½).
The Solution
Starting Material Number of Half
Lives
10 grams
1
Years Passed
4 years
Ending Material
5 grams
Let’s practice with on
from your packet
1. What is the half life of a 100 gram sample of
nitrogen-16 that decays to 12.5 grams of nitrogen-16
in 21.6 seconds?
Underline the important information
Let’s practice with on
from your packet
1. What is the half life of a 100 gram sample of
nitrogen-16 that decays to 12.5 grams of nitrogen-16
in 21.6 seconds?
Starting Material
100 grams
Number of Half
lives
0
Time Passed
0 seconds
Ending Material
100 grams
Let’s practice with on
from your packet
1. What is the half life of a 100 gram sample of
nitrogen-16 that decays to 12.5 grams of nitrogen-16
in 21.6 seconds?
Starting Material
Number of Half
lives
Time Passed
Ending Material
100 grams
0
0 seconds
100 grams
100 grams
1
x
50 grams
Let’s practice with on
from your packet
1. What is the half life of a 100 gram sample of
nitrogen-16 that decays to 12.5 grams of nitrogen-16
in 21.6 seconds?
Starting Material
Number of Half
lives
Time Passed
Ending Material
100 grams
0
0 seconds
100 grams
100 grams
1
x
50 grams
50 grams
2
2x
25 grams
Let’s practice with on
from your packet
1. What is the half life of a 100 gram sample of
nitrogen-16 that decays to 12.5 grams of nitrogen-16
in 21.6 seconds?
Starting Material
Number of Half
lives
Time Passed
Ending Material
100 grams
0
0 seconds
100 grams
100 grams
1
x
50 grams
50 grams
2
2x
25 grams
25 grams
3
3x
12.5 grams
Let’s practice with on
from your packet
1. What is the half life of a 100 gram sample of
nitrogen-16 that decays to 12.5 grams of nitrogen-16
in 21.6 seconds?
Starting Material
Number of Half
lives
Time Passed
Ending Material
100 grams
0
0 seconds
100 grams
100 grams
1
x
50 grams
50 grams
2
2x
25 grams
25 grams
3
3x
12.5 grams
21.6 = 3x
7.2 = x
What to be working on
1. Half-Life Worksheet
2. Relative Dating Worksheet
3. Fun with Stratigraphy worksheet
4. Mesozoic Article
5. Ask me