MODELING RADIOACTIVE DECAY
1. Place 100 sunflower seeds into a box with all seeds pointing to the right.
2. Shake the box gently from side to side. Stop after ten seconds
3. Remove and count the seeds that “point” to the left side of the box.
4. Record in your data table the number of seeds removed.
5. Repeat steps 2-4 until all seeds have been counted and removed.
6. Calculate the cumulative number of seeds removed for each time interval.
7. Make a graph using your group’s data. Plot “cumulative number of seeds” on Y-axis.
Plot “time (seconds)” on the X-axis.
DATA TABLE
Rate of Radioactive Decay
Time
(seconds)
10
Number of
seeds removed
Cumulative number
of seeds removed
20
30
40
50
60
70
80
90
100
Analysis:
1. Explain what the seeds at the beginning of the experiment represent in terms of
radioactive decay.
2. Identify what the removed seeds represent in each step.
3. Calculate the half-life of your sample, in seconds, that is represented in this activity
(number of trials it took to remove 50 seeds multiplied by 10 sec/trial).
4. Calculate the age of your samples in years, if each 10-second interval represents 5,730
years (number of trials X 5,730 years/trial).
5. What is meant by half-life?
6. Thorium-232 is a radioactive isotope that has a half-life of 14 billion years. Thorium
232 decays into Uranium 233. If a fossil was discovered that had 50 grams of Thorium
and fifty grams of uranium, how old would the fossil be?
7. Using the information above, If a fossil had 25 grams of thorium and 75 grams of
uranium, how old would the fossil be?