Name: Jennifer Miyashiro

Topic: Uranium-238 Decay Series

Grade Level: 10 – 12

Course: Chemistry in the Community

Target Class Size: 25 - 30

Objective:

The students will construct a graph that demonstrates the decay of Uranium-238.

Materials:

  • Cards for each of the major decay products
  • Blank graph on which to plot decay series
  • Periodic table of the elements

Assessment: Accuracy of plotted decay series and answers to questions.

214
84 / Po
1.6x10-4 s / 210
84 / Po
138 d / 218
84 / Po
3 min
206
82 / Pb
Stable / 210
82 / Pb
19.4 y / 214
82 / Pb
27 min
234
90 / Th
24 d / 230
90 / Th
8x104 y / 210
83 / Bi
5 d
238
92 / U
4.5x109y / 234
92 / U
2.5x105y / 234
91 / Pa
1.17 min
214
83 / Bi
19.7 min / 226
88 / Ra
1620 y / 222
86 / Rn
3.8 d

URANIUM – 238 DECAY

Directions:

Below is a set of cards. Each card contains a major product of the uranium – 238 decay series.

1.Fill in the missing information on the decay product cards (You will probably need your periodic table).

  1. Cut the cards out.

Each card is supposed to contain the following information:

Mass Number
Atomic Number / Chemical Symbol
Half - Life
214
84 / 1.6x10-4 s / 210 / Po
138 d / 218
84 / 3 min
206
82 / Stable / 210 / Pb
19.4 y / 214
82 / 27 min
234 / Th
24 d / 230
90 / 8x104 y / 210
83 / 5 d
238
92 / 4.5x109y / 234 / U
2.5x105y / 234
91 / 1.17 min
214
83 / 19.7 min / 226 / Ra
1620 y / 222 / Rn
3.8 d

Directions (continued):

  1. Place the cards in the correct square (based on mass number and atomic number).
  2. Draw an arrow that connects each decay product to the one that it will decay into. This will take a little thought (make sure that the nuclear equations for alpha and beta decay would be balanced).
  3. Next to each arrow, label if the isotope undergoes alpha-decay or beta-decay to get to the next isotope in the decay series.
  4. Check your work over carefully.
  5. Glue the cards down.
  6. Color each of the elements a unique color (hint: you will need 8 colors).
  7. Color the alpha – decay arrows a unique color.
  8. Color the beta – decay arrows a unique color.
  9. Answer the questions.

Questions:

  1. What were the first and last isotopes in the decay series?
  1. Which isotope has the longest half – life? How long is it?
  1. Which isotope has the shortest half – life? How long is it?
  1. Fill in the following table for radon – 222.

Time Elapsed

/ % of Rn – 222 remaining
  1. Approximately, what is the sum of all the half – lives in this decay series?
  1. Which of these isotopes would give off the most amount of radiation in a short period of time? Explain your reasoning.
  1. Generally, a radioactive isotope is considered “safe” after ten half – lives. How long is that time period for U – 238?

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URANIUM – 238 DECAY SERIES

ATOMIC NUMBER / 92
91
90
89
88
87
86
85
84
83
82
81
206 / 210 / 214 / 218 / 222 / 226 / 230 / 234 / 238
MASS NUMBER

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STRUCTURE OF ATOMS½ life Worksheet

In the following problems, an original sample of mass m0 decays over time, t, to a mass of mt. The half-life of the isotope is given as t1/2. In each problem, calculate the value of the missing variable.

Question / m0 / t / mt / t1/2
1 / 64g / 4 half lives / ? / N/A
2 / 32g / 8.0yr / ? / 2.0yr
3 / 128g / 5d / ? / 24hr
4 / 50.0g / 8.0min / ? / 1.6min
5 / 30.0g / 9840yr / ? / 2460yr
6 / 60.0g / ? / 3.8g / 4.3 x 106yr
7 / 400.0g / ? / 50.0g / 13.6d
8 / 1.0000g / ? / 0.15625g / 2325yr
9 / ? / 40.0min / 1.00g / 10.0min
10 / ? / 16.2yr / 2.5g / 3.24yr
11 / 64.0g / 18min / 1.0g / ?
12 / 18.00g / 12.5d / 0.562g / ?

Adapted from:

Newton,David, Chemistry Problems. Portland: J. Weston Walch, 1984

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