Name
Date
Exploring nuclear decay – Beta Decay


Go to PhET Simulations. Find and open the sim called Beta Decay.
http://phet.colorado.edu/simulations/sims.php?sim=Beta_Decay
Click on ‘Run Now’ to start the simulation. When the simulation
opens click on the ‘Single Atom’ Tab.
After the simulation begins, follow the instructions below and
answer the questions that follow each instruction.
1. Watch the Hydrogen-3 (3H) nucleus until it decays. Click ‘Reset
Nucleus’ and watch it again. Repeat this at least 8 times. List at least 3 observations that
compare the 3H nucleus before and after it decays.
2. Click on the ‘Reset Nucleus’ button and run the program again, but this time click the
‘Pause’ button
immediately after a decay so you can look at what comes flying out of the
nucleus. Describe what you observe.
3. Why does the Hydrogen (3H) nucleus become a Helium (3He) nucleus after it decays? (You
may have to look at a Periodic Table to determine this.)
4. Why doesn’t the mass number change after Hydrogen-3 (3H) decays to Helium-3 (3He)?
5. Select the Carbon-14 (14C) nucleus and run the simulation. Do this at least 8 times. List at
least three observations that compare the Carbon-14 nucleus before and after it decays.
6. Describe the similarities and differences you observed between 3H decay and 14C decay.
7. Look at the Decay Time Chart across the top of the screen. It should display the decayed
nuclei of all of the previous trials you watched. Describe any pattern for the decay times that
are represented on the chart. Does this indicate that the decay of a specific nucleus is a
predictable pattern or random?
8. Now click on ‘Multiple Atoms’ and quickly dump about 50 3H nuclei by rapidly clicking the
‘Add 10’ button until the ‘Bucket o’ Atoms’ five times. Watch the atoms decay and watch
the ‘Decay Chart’ across the top. List 3 observations concerning the decay. Print out the
screen if possible or draw what the Decay Chart across the top looks like.
9. Click on the pause button and then click on ‘Reset All Nuclei’ button. Be prepared to make
observations. Run the program. Is the pattern of decayed nuclei across the top the same as it
was the first time? Print out the screen or copy the Decay Chart on your paper. You might
have to repeat this a few times to be sure of your answer. Describe any similarities and/or
differences in what you see when you do this.
10. Use the timeline on the top of the simulator as 11. Make a graph of the data, plotting time
a timer. Click on ‘Reset All Nuclei’ again and
on the horizontal axis and the number of
click the ‘Pause’ button every 5 years to take
Hydrogen-3 nuclei on the vertical axis.
your data. Make a data table in the space on
Label your axes. You will need to pick
the right showing the time in 5 year
the best scale for both axes so the data
3
increments and the number of H nuclei left
fits nicely on the graph. Does the graph
after each 5 year time period. What should
resemble any mathematical function you
the first data point for everyone be?
know of, for example a straight line
(linear), parabolic, exponential or other?
Data Table
12. EXTRA CREDIT: Using the Custom Nucleus and all the nuclei in the bucket, what half-life
do you have to use so that it takes 20 years for all of the nuclei to decay.