Name ___________________________________
Phet Simulation
Alpha Decay
Quick Review Practice (not scored) – Turn to the periodic table in the very back of your physical
science book.
The atomic number is written above the element’s symbol and tells you how many protons the element
has.
1) How many protons does an atom of the element silver (Ag) contain? ___
Answer: 47
The atomic mass is written below the element’s name and represents the number of protons and average
number of neutrons added together.
2) What is the atomic mass of an atom of the element of arsenic (As)?
Answer: 74.9222 amu
Isotopes are atoms of an element varying in the number of neutrons they have. Carbon atoms contain 6
protons. Carbon-12 is a carbon atom with 6 protons and 6 neutrons. Carbon-14 is a carbon atom with 6
protons and 8 neutrons. Carbon-12 and Carbon-14 are isotopes of carbon.
3) How many neutrons does a Uranium-235 isotope have? (Hint – find uranium’s atomic number on
the periodic table)
Answer: 143 neutrons,
235 – 92 = 143
Go to Phet Simulations. Find and open the sim called Alpha Decay.
http://phet.colorado.edu/simulations/sims.php?sim=Alpha_Decay
Click on
‘Run
Now’
Run
Now
and when the simulation opens click on the Single Atom
LOOK at the ‘Legend’ on the top right of the simulation. Use the three questions below to
check before proceeding. (1 pt)
What color particle represents a proton? ______
What color particle represents a neutron? _______
An alpha particle consist of ____ protons and ____ neutrons
This simulation will show the decay of a Polonium-211 atom.
1) Using your periodic table, a Polonium-211 atom has _______ protons and _______ neutrons. (1 pt)
Watch the Polonium-211 atom until it decays. Click ‘Reset Nucleus’ and watch it again. Repeat
this at least 8 more times.
2) How does the Polonium-211 atom compare BEFORE and AFTER it decays (2pts)
3) Click the Pause button immediately after a decay so you can look at the particle that comes
flying out of the nucleus. What kind of particle comes flying off? (1 pt)
A) One Neutron
B) One Alpha Particle
C) One Proton
4)Why does the mass number change from 211 to 207 after a decay? (2pts)
5) Look back at your periodic table. Why does the Polonium (Po) atom become Lead (Pb) after a
decay (2pts)
5) 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. Did all of the Po-211 atoms decay at the half-life mark
(red line)? _______ (1 pt)
Multiple
Atoms
6) Now click on
‘Multiple
Atoms’ and press the pause button. Empty the Bucket o’
Polonium by clicking the ‘Add 10’ button until the bucket is empty. Hit the play button and when you
reach the half life mark click pause. Use the data chart below to record the amount of Po-211 and Pb-207
atoms. Reset All Nuclei and repeat 4 more times. (2 pts)
Trial Number of 211 Po Atoms
1
2
3
4
5
Number of 207 Pb Atoms
7) Using your data above, at the half life mark, what happens? (1 pt)
A) All of the Po-211 decays
B) Some of the Po-211 decays
C)About Half of the Po-211 decays D) None of the Po-211 decays
Extra Credit (8 bonus points possible)
8) Click on ‘Reset All Nuclei’ again and this time click the Pause button every half second. Use the data
chart below to record the number of Po-211 atoms remaining at each point. (2pts)
Time
0
0.5
1
1.5
2
2.5
3
Number of 211 Po Atoms
100
9) On the right side bar, under ‘Choose Nucleus’, select custom. Set the half life line to 1 second. Predict how these
custom atoms will decay compared to the Po-211 atoms above. (2pts)
10) Empty the bucket of atoms and repeat step 8. (2pts)
Time
0
Number of Custom Atoms
100
0.5
1
1.5
2
2.5
3
11) Was your prediction correct? Explain using the data charts in Step 8 and 10. (2pts)