Half-Life Data Worksheet
Name:
Date:
Follow the directions and answer the questions.
The following image shows how uranium-238 (a radioactive element) decays and changes to a stable
element (lead-206). The half-life of each element is shown in years and days.
1. Hypothesize what half-life is:
The Uranium-238 Decay Chain
Atomic Number
83 84 85 86 87 8
Only main decays are shown
Gamma emitters are not indicated
Pb-214
26.8 m
a
Po-218
3.05 m
P
Pb-210
22.3 a
s
Bi-214
19.9 m
N
a
P
Po - 214
-4
1.64*10 S
p
^ Bi-210
5.0 d
\,
P
Pb-206
Stable
a
Po-210
138.4 d
89
90
91
92

Th-234
a
U-238

24.1 d

4.5x109a

P
Pa-234
1.17m
N,
P
a
Th-230
a
U-234

7.7x104a

24x105a
Element Names
U - uranium
Th - thorium
Ra - radium
Pa - protactinium
Rn - radon
Po - polonium
Bi - bismuth
Pb - lead
Half-life units
a - years
d - days
h - hours
m - minutes
s- seconds
Observe the half-life demonstration as directed by your teacher.
2. Calculate the number of radioactive atoms remaining after each half-life. Write the number of
atoms in the "Number of Radioactive Atoms" column. Plot the number of radioactive atoms on the
graph provided. Note that the number of unstable (radioactive) atoms decreases as they are being
transformed into stable atoms.
Half-Life
Number of
Number
Radioactive

Atoms
0
1024
1

2

3

4

5

6

7

8

9

10

1000		
900		
>s\
| 800			
* 700		
>
'5 600		
ra
o
*5 500		
ra
cc
g 400		
ii 300		
E
= 200		
100	
0											
0123456789 10
Half-Life Number
^ rnA United States _	RadTown Radioactive Atom Activity Set	EPA 402-B-19-025
JbNWl Environmental Protection	'
* * Agency	https://www.EPA.gov/RadTown/Activity-5-Half-Life

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3. If you had a sample of 4,000 radioactive atoms, how many atoms would remain after 5 half-lives?
Half-Life
Number
Number of
Radioactive
Atoms
0
4000
1

2

3

4

5

4. If you had a sample of 210 atoms, and you started with a sample of 3,360 atoms, how many half-
lives have elapsed?
5. If the half-life of the sample from question 2 is 30 minutes, how many hours did it take to decay
from 3,360 atoms to 210 atoms?
6. Can you determine the age of something (like a fossil) by examining its half-life? Explain.
7. In what other ways might it be useful to know a sample's half-life?
^pp/v Environmental Protection RaclTown Radioactive Atom Activity Set	EPA 402-B-19-025
* * Agency	https://www.EPA.gov/RadTown/Activity-5-Half-Life

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