7.2 PhET LAB: Alpha Decay Name: ______________________
OBJECTIVE: explain the alpha decay process; complete radioactive decay equations; define and analyze halflife through applying the PhET “Alpha Decay” simulation at
...
7.2 PhET LAB: Alpha Decay Name: ______________________
OBJECTIVE: explain the alpha decay process; complete radioactive decay equations; define and analyze halflife through applying the PhET “Alpha Decay” simulation at http://phet.colorado.edu.
Open/Run Alpha Decay at http://phet.colorado.edu.
Take 5 minutes to freely explore the sim.
Investigating Alpha Decay
1. Start on the SINGLE ATOM tab. Observe the decay of Polonium-211. After each decay, press the RESET
NUCLEUS button to watch the process again. Write a description of alpha decay for Po-211.
In the alpha decay of Po-211 what happens is after a period of time the unstable Polonium will try to
achieve a more stable state by releasing an alpha particle. The alpha particle is composed of 2 protons and
2 neutrons. As such the mass number will go down by 4 and the atomic number by 2. Due to the atomic
number changing the Polonium is now Lead and has an atomic weight of 207.
Complete the following alpha decay equations, using http://www.chemicalelements.com as a resource:
2. Polonium-211: 211 84Po→207 82Pb+2 4α 3. Radium-226:
¿¿
¿
¿ 2α
4 ¿
¿¿ ¿
¿
226 88Ra →¿
4. Uranium-238:
¿¿
¿
¿¿¿→234 90T h+2 4α
¿¿U¿
5. Plutonium-240:
¿
¿236¿ 42α
Pu
94
240
→¿ 92¿¿¿U¿
6. Americium-241: 241 95Am→237 93Np+2 4α
7. How is alpha decay used in everyday life? (give at least two uses)
Alpha decay is used in cancer treatment as the alpha particles from cobalt-60 can kill cancer cells.
Alpha decay is also used in smoke alarms as the alpha particles are positively charged and can attract
electrons creating an electric charge and smoke disrupts that charge.
Investigating Half-Life of Alpha Decay
8. Click the MULTIPLE ATOMS tab. Execute five trials to determine the number of parent and daughter
nuclei at one half-life. Complete the table below.
Parent Nuclei
Po-211
Parent Nuclei
(remaining nuclei)
[yellow]
Daughter Nuclei
(decayed nuclei)
[black]
100 50 50
80 38 42
60 25 35
9. Define half-life.
The half-life of an element is the amount of time for a quantity of it to have undergone decay and only have
half the original amount remaining.
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10. Suppose a substance has a half-life of 0.52 s. Create accurate pie charts showing the number of
remaining parent nuclei and decayed daughter nuclei (shade slightly) starting with 40 total nuclei.
20 10 5 2
20 30 35 38
11. Use the PhET alpha decay simulation to test your scenario copying each pie chart. Use the Multiple
Atoms setting and hit the pause button at the bottom. Select the Custom button so that you can change the
half-life. Click on Add 10 four times to add 40 atoms. On the half-life scale, you need to approximate the
half life time as ½ a second by sliding the double-headed arrow. Click start and pause when the top row
atom reaches ½ a second. Copy down the pie chart below. Repeat the “play”, “pause” and “copy the pie
chart” for the other three times (approximate those times as 1 sec, 1 ½ sec, and 2 sec).
22 10 3 2
18 30 37 38
12. How does your prediction match with the results of the simulation? Convey with actual values from the
simulation and a calculation of percent difference on 0.52 seconds.
My prediction values are very similar to the actual values given by the sim with only a 0.001% difference.
13. Run three trials and complete the data table below. Include uncertainty.
PREDICTION with VALUES:
SIMULATION with VALUES:
Number of Decayed Daughter Nuclei (n/nuclei)
Trial 1 Trial 2 Trial 3
Average
1¿±¿
0.52 16 19 18 18
1.04 28 32 29 30
1.56 32 34 35 34
2.08 36 39 39 38
2.60 38 39 40 39
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