Name______________________________________Per. ________Date______________
Nuclear Fission Phet Simulation Activity
Go to Phet Simulations at phet.colorado.edu. Find and open the simulation called Nuclear Fission, or go to:
http://phet.colorado.edu/simulations/sims.php?sim=Nuclear_Fission Click on “Run Now.”
For questions about isotopes of uranium, go to: http://en.wikipedia.org/wiki/Isotopes_of_uranium
Fission – One Nucleus:
Click on the “Fission: One Nucleus” tab. Experiment with
shooting the neutron gun and watch what happens.
1) What happens when the U-235 nucleus is first “hit” with
a neutron? What isotope is made?
What does Wikipedia say about this isotope? If it didn’t
fission, where would it end up?
2) What happens after the isotope fissions? What products
are made? Be specific in your answers below.
What is the daughter isotope, according to the decay
chain to the right? (look at the first decay only)
What type of decay is this? _____________________________
What particle(s) should come off in this type of decay?
(look up alpha, beta, or gamma decay)
Watch the simulation, what type of small particles does
the simulation show being emitted after the fission process? ______________________ Is this accurate? _______
What is the final, stable isotope at the end of the U-235 decay chain (look at the diagram above)?
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.
3) Click the ‘Reset All’ button and then set the initial number of U-235 nuclei to 100 and U-238 to 0. What
happens when you fire the neutron gun?
4) Explain what makes this a “chain reaction”.
5) Click ‘Reset’ and then set the initial number of U-238 nuclei to 100 and U-235 to 0. Explain what
happens when you fire the gun. Does this cause a chain reaction? Try multiple times to start a chain
reaction with the U-238. Explain why this happens. See U-238 the Wikipedia website for an
explanation.
Look up U-239, the product of neutron bombardment of U-238 in a
reactor.
What is U-239’s half life? _______________________________
nuclear
What is the final product in the decay series for U-239? ___________
What is its half-life? _________________
What does the Wikipedia site say about the use for this final product in
the U-239 decay series?
6)
Set the initial numbers of U-235 nuclei and U-238 nuclei to the numbers in the table below. Record
your results.
U-235
U-238
% of 235U fissioned
after 1 firing
# firings required to
fission all 235U
100
0
70
30
50
50
30
70
0
100
N/A
What happens to the reaction as the proportion of U-238 nuclei increases? Explain why this happens.
7) If you were trying to design the most efficient nuclear fission reactor possible, what ratio of U-235 to U238 would you want? Explain why.
8) Look up the percentage of U-235 and U-238 in naturally occurring uranium:
_____________%U-235
_________________% U-238
What does this imply about what must be done to uranium ore in order to use it in a nuclear reactor?
Why do you think they call the processing of uranium ore “enrichment?” This website might help in
your understanding: http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Conversion-Enrichmentand-Fabrication/Uranium-Enrichment/
Nuclear Reactor:
Select the “Nuclear Reactor” tab at the top. Click on the picture box, so you can see what actual rods in a
nuclear reactor look like. Experiment with changing the height of the control rod adjustor and firing the
neutrons and watch what happens. Then answer the questions below.
9) 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?
b) What happens if the neutrons hit a control rod?
10) 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.
11) If the purpose of a nuclear reactor in a power plant is to produce energy, why are there control rods?
12) One way to control the temperature in a nuclear reactor is to keep the control rods fully/mostly
inserted, and then keep firing neutrons into the reactor every time the nuclear chain reaction dies
down. What would be a disadvantage of this method?
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?