DO NOT WRITE ON THIS PAPER…RECORD ALL ANSWERS ON THE ANSWER SHEET
Everything around you is made of atoms, including plants, animals, people, water, furniture and buildings.
Each atom contains tiny particles called protons and neutrons in its center, or nucleus. The number of
protons in the nucleus determines which element the atom belongs to. For example, all hydrogen atoms
have one proton, and all carbon atoms have six protons.
Within a particular element, atoms with different numbers of neutrons are called isotopes. Carbon-12 and
carbon-14 are two different isotopes of carbon. Carbon-12 has 6 protons and 6 neutrons, while carbon-14
has 6 protons and 8 neutrons. Unlike carbon-12, carbon-14 is an unstable or radioactive isotope. Like a
kernel of popcorn in the microwave, an unstable nucleus can suddenly change in a burst of energy. This
process is called radioactive decay, and the resulting stable atom is a daughter product. The stable
daughter product of carbon-14 decay is nitrogen-14, which has 7 protons and 7 neutrons.
1. Define the term Half-life.
2. Examine the graphs below. These graphs represent the decay of two specific isotopes. Use the
graphs to determine the half-life of the isotopes (128 atoms were present before decay began).
Record your answers on the answer sheet.
Graph #1
Graph #2
Go to the following website: www.explorelearning.com
Log in using the following username and password: tyanka
science
Type “half life” in the search box (upper right corner)
Select “Launch Gizmo” under the Half-life activity
Under the “User Choose Half-life” tab, select “Isotope A”. Also, check to be sure that your settings are for
“Random Decay” and that 128 atoms are present of Parent Material.
Select the “play” button to begin decay and study the Table, Bar Chart, and Graph on the right of the
page. Determine the Half-life of Isotope A and record this on your answer sheet.
Reset the Gizmo and select “Isotope B”. Determine the Half-life of this isotope and record your answer.
Be sure to use the Table, Bar Chart & Graph to help find the correct answer.
CONTINUE ON BACK OF PAPER
Set your Gizmo to each of the scenarios below (begin with Scenario #1). Use the “Table” Tab and graph
the data generated by this scenario. Include a data point for each 10 second interval. Be sure to label
this curve (HL=35) or use different color pens/pencils for each of the 3 scenarios you will graph.
Your graph should contain 3 curves, each of which is labeled or color coded (with a key)
Scenario #1
Half-Life = 35 seconds
Sample = 120 atoms
 Graph the number of radioactive atoms (red) over time
Scenario #2
Half-Life = 20 seconds
Sample = 120 atoms
 Graph the number of radioactive atoms (red) over time
Scenario #3
Half-Life = 10 seconds
Sample = 120 atoms
 Graph the number of radioactive atoms (red) over time
Follow Up Question
Compare the 3 curves that represent the radioactive atoms over time. How does the (initial) slope of each curve relate
to the half-life of the substance? Explain your answer below.
Answer the following Multiple Choice Questions (on the answer sheet)
1.
Two scientists are experimenting with pure samples of isotope X, a highly radioactive substance. The first
scientist has a sample with a mass of 20 grams. He measures a half-life of 232 seconds. The second scientist
has a sample of the same substance with a mass of 80 grams. What is the half-life that she is most likely to
measure?
a. 26
c. 232
b. 58
d. 464
2. Radioactive isotopes can be used to find the age of rocks, fossils, or other artifacts. Carbon-14 has a half-life
of 5,730 years. Suppose a sample of charcoal from a primitive fire pit contains one eighth of its original
amount of carbon-14. How old is the sample?
a. 716 yearss
c. 22,920 years
b. 17,190 years
d. 45,840 years
Name _________________________________
Answer Sheet
Explore Learning: Half-life Activity
1.__________________________________________________________________________________
__________________________________________________________________________________________
2. Graph #1: Half-life = ________ sec
Graph #2: Half-life = _________sec
**From the website…
Half-life of Isotope A:_____sec
Half-life of Isotope B:_____sec
Remember to include a title, labels, and units (x & y) on your graph below. Be sure to indicate which
curve belongs to which data set (color code, different lines, etc.)
Graph the Independent Variable on the X-axis & Dependent Variable on the Y-axis
(title)
0
100
200
(Label & Units)
over
Follow Up Question__________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
Multiple Choice: 1)_____
2)_____
Additional Half-life Practice Problems