PhET Activity for MS-ESS1-4: Radioactive Dating Game

DIRECTIONS:
1. You should be on the 'Half Life' tab with 'Carbon-14' selected by default.
2. Locate the 'Bucket o' Atoms' and click the 'Add 10' button twice to add 20 Carbon-14 atoms to the screen.
3. Click the play button at the bottom of the screen to start the simulation.
4. Observe how the Carbon-14 atoms (red spheres) randomly change into Nitrogen-14 atoms (blue spheres). Notice the pie chart on the right and the graph at the top.
Spend 2-3 minutes exploring this tab. Watch the pie chart and the graph at the top. What do you notice about the decay of individual atoms? You can pause and reset the simulation using the buttons at the bottom. Try adding more or fewer atoms.

QUESTION: Are you acquainted with the tools in this simulation?

DIRECTIONS:
1. Click the 'Reset All Nuclei' button at the bottom right.
2. Click the 'Add 10' button twice to add 20 Carbon-14 atoms.
3. Click the play button and watch the atoms decay. Pause the simulation when exactly half (10) of the atoms have decayed. Note the time on the graph at the top.
4. Click the 'Reset All Nuclei' button again and repeat steps 2 and 3. Compare the time it took for half the atoms to decay this time.

QUESTION: Did it take the exact same amount of time for half the atoms to decay each time you ran the experiment? Based on your observations, describe why scientists refer to radioactive decay as a random process for a single atom but a predictable process for a large group of atoms.

DIRECTIONS:
1. Click the 'Reset All Nuclei' button.
2. Click the 'Add 10' button once to add 10 Carbon-14 atoms.
3. Click the play button and immediately pause it after the very first atom decays.

QUESTION: When a Carbon-14 atom decays, what does it become?

DIRECTIONS:
1. Click the 'Uranium-238' radio button in the 'Choose Isotope' panel on the right.
2. If there are any atoms on screen, click 'Reset All Nuclei'.
3. Click the 'Add 10' button to add 10 Uranium-238 atoms.
4. Click the play button and let the simulation run. Observe how long it takes for a single U-238 atom to decay, if it does at all during the time you watch.

QUESTION: Uranium-238 decays into ___ -206. Compared to Carbon-14, Uranium-238 has a much ___ half-life, meaning its atoms decay much more ___.

(a)  

DIRECTIONS:
1. Click on the 'Decay Rates' tab at the top of the screen.
2. If it is not already selected, click the 'Carbon-14' radio button on the right.
3. Click 'Reset All Nuclei'.
4. Drag the handle on the 'Bucket o' Atoms' all the way to the top to add the maximum number of atoms.
5. Click the play button and observe the graph as the atoms decay.

QUESTION: Pause the simulation when the time is at one half-life (approximately 5700 years). What is the approximate percentage of Carbon-14 remaining?

DIRECTIONS:
1. If you are not there already, reset the simulation in the 'Decay Rates' tab, add a full bucket of Carbon-14, and press play.
2. Let the simulation run until the time reaches two half-lives (approximately 11,400 years).
3. Pause the simulation and observe the pie chart and the graph.

QUESTION: After two half-lives, the percentage of the original Carbon-14 atoms remaining is about (a)   .

DIRECTIONS:
1. In the 'Decay Rates' tab, click the 'Reset All Nuclei' button.
2. In the right panel, select the 'Uranium-238' radio button.
3. Add a full bucket of Uranium-238 atoms and press play.
4. Observe how slowly the graph changes compared to the Carbon-14 graph you saw earlier.

QUESTION: Why is Carbon-14 (half-life ~5,700 years) useful for dating things that are thousands of years old, while Uranium-238 (half-life ~4.5 billion years) is used for dating objects that are millions or billions of years old?

DIRECTIONS:
1. Click on the 'Measurement' tab at the top of the screen.
2. Ensure 'Tree' is selected in the 'Choose an Object' panel and 'Carbon-14' is the selected probe.
3. Click the 'Plant Tree' button and wait for it to grow.
4. Use the probe to measure the C-14% in the living tree and in the air. Note the values.
5. Click the 'Kill Tree' button.

QUESTION: Why does the amount of Carbon-14 in the tree only start to decrease after the tree dies?

DIRECTIONS:
1. Ensure you have a dead tree on the screen from the previous step in the 'Measurement' tab.
2. Let the simulation time advance. The graph will plot the age of the tree vs. the C-14 percentage.
3. Drag the probe to the dead tree and pause the simulation when the C-14 percentage is exactly 50%.

QUESTION: As the dead tree ages, the percentage of Carbon-14 ___. An object with 50% of its original Carbon-14 is approximately ___ years old.

(a)  

DIRECTIONS:
1. In the 'Measurement' tab, click the 'Rock' radio button in the 'Choose an Object' panel on the right.
2. Click the 'Erupt Volcano' button.
3. After the eruption, click the 'Cool Rock' button to solidify the lava.

QUESTION: For dating this volcanic rock with Uranium-238, what event 'starts the clock' for the decay process?