Nuclear Fission Simulation
Click on the Nuclear Fission simulation to help you answer the following questions:
http://phet.colorado.edu/simulations/sims.php?sim=Nuclear_Fission
Part 1: Fission - One Nucleus
Select the tab that says “Fission: One Nucleus‟ and click on “Run Now”.
Experiment with shooting the neutron gun and watch what happens.
1. ​Try to figure out, how can you make Uranium-235 unstable?
2. How do you know U-235 is unstable? In your own words, what does “unstable” mean
when used to describe the isotope?
3. What happens when the U-235 nucleus is “hit” with a neutron? There are a number of
things that happen here, describe all of them in as much detail as you can. Use the
pause button when needed.
4. Imagine that you have many U-235 atoms and you fire a neutron at one of them. What
do you think will happen? Explain your prediction.
Part 2: Chain Reaction
Select the “Chain Reaction” tab at the top. Experiment with changing the settings and
shooting the neutron gun and watch what happens. Then answer the questions below.
5. Click the “Reset All‟ button and then set the initial number of U-235 nuclei to 100 and
U-238 nuclei to 0. What happens when you fire the neutron gun? Does this cause a
chain reaction?
Nuclear Fission Simulation
6. If you wanted to explain nuclear chain reactions to someone, what would you tell
them? Briefly, explain your ideas using appropriate vocabulary. Make sure your answer
explains why the reaction occurs AND what affects the speed of the reaction.
7. Set the initial numbers of U-235 nuclei and U-238 nuclei to the numbers in the table
below. Repeat each trial multiple times and record the value that occurs most often.
U-235
100
70
50
30
0
U-238
0
30
50
70
100
% of U-235
fissioned after 1
firing
# firings required
to fission all
U-235
N/A
8. What happens to the reaction as the proportion of U-238 nuclei increases? Explain why
this happens.
9. Why do you think U-235 a good isotope of Uranium for creating chain reactions?
Part 3: Nuclear Reactor
Select the “Nuclear Reactor” tab at the top. Experiment with changing the settings
and firing the neutrons and watch what happens. Then answer the questions below.
10. Watch very closely to the fission reactions as they happen. Specifically watch what
happens to the loose neutrons after the reaction.
a. What happens if the neutrons hit another nucleus?
Nuclear Fission Simulation
b. What happens if the neutrons hit a control rod?
11. Compare the chain reaction that occurs when the control rods are inserted further
into the reactor versus when they are pulled all/mostly out of the reactor:
12. If the purpose of a nuclear reactor in a power plant is to produce energy, why do you
think are there control rods?
13. The bar graphs on the right of the display show the “Power Output” and the “Energy
Produced”. What is the difference between these two quantities?
Part 4: Developing Nuclear Bombs
14. Now let’s say you are a government researcher who wanted to make a nuclear bomb.
Use an Internet search to determine which materials are used for nuclear bombs.
(Remember, a bomb must be transportable – what do you need to do so that it is
transportable?) What do you need to make the bomb explode?
15. While using the simulation, what observations have you made that makes nuclear
reactions good for nuclear bombs?