Radioactivity has given us more than just Spiderman. It can also be used to figure out how many BILLIONS of years old something is. Bring pennies. Register to explore the whole course here: https://school.bighistoryproject.com/bhplive?WT.mc_id=Slideshare12202017

1. TEACHER MATERIALS
Page 1
MODELING MEASURING TIME USING RADIOACTIVITY
BIG HISTORY PROJECT / LESSON 1.4 ACTIVITY
Process
Ask students to get into small groups and give each group a
cup filled with 100 pennies. Tell students that they are to do the
following:
• Toss all 100 pennies onto the table
• Remove the pennies that land tail-side up on the table, and
place them flat on the table, arranged in a tall column.
• Gather the remaining pennies and toss them again. Remove
the pennies that land tail-side up and arrange them in a
second column, next to the first column.
• Repeat until all the pennies have been removed.
• If no pennies come up tails on a toss, leave an empty
column.
Columns that the students make should look something like this
image.
Explain to students that the chance that any penny will come up
tails is always the same: 50 percent. This is why after each toss,
approximately half of the pennies are removed.
Tell students that in this model, the removal of a penny signifies the decay of
a radioactive nucleus. The time it takes for half of the remaining pennies to be
removed is called the half-life. Since each penny has a 50 percent chance of
decaying (or coming up tails) each time it’s tossed, the half-life of the pennies in
this model is about one toss.
Have the students count the number of columns they made during this first
round of their experiment. Now, have students gather up all their pennies and
conduct the experiment again. This time, they’ll plot the number of tail-side up
pennies on the worksheet.
Have groups write their answers to the three questions on the worksheet, and
then have them share with the class.
1. How many columns, or half-lives, did your pennies have in the first round
of your experiment? How about in the second round?
2. Did you ever have exactly half of your pennies come up tails?
3. What if we did this experiment again, like this: Each student in class
has a penny and everyone tosses their pennies at the same time. Those
students whose pennies landed tail-side up, had to sit down. About how
many students do you think would sit down after one half-life? After two
half-lives? How many half-lives do you think your “radioactive” class has?
Note: This activity is an adaptation of material produced by the Exploratorium Teacher Institute.
Preparation
Gather materials needed:
• 100 pennies per group of students
• A cup or container to hold the pennies
Purpose
The video you watched in the last activity (How Old Is the Earth?) explained that the Solar System is over 4 billion years old. In this activity, students will learn about
radioactive decay and the concept of half-life, which scientists use to measure extremely old things.

2. Name: Group Name:
STUDENT MATERIALS
Page 1
MODELING MEASURING TIME USING RADIOACTIVITY
BIG HISTORY PROJECT / LESSON 1.4 ACTIVITY
Purpose
The video you watched in the last activity (How Old Is the Earth?) explained that the Solar System is over 4 billion years old. In this activity, you’ll learn about
radioactive decay and the concept of half-life, which scientists use to measure extremely old things.
Process
Get into small groups. Your teacher will distribute a cup filled with 100 pennies to each group. As a group, do the following:
• Toss all 100 pennies onto the table.
• Remove the pennies that land tail-side up on the table, and place them flat on the table, arranged in a tall column.
• Gather up the remaining pennies and toss them again. Remove the pennies that land tail-side up and arrange them in a second column, next to the first
column.
• Repeat until all the pennies have been removed.
• If no pennies come up tails on a toss, leave an empty column.
The chance that any penny will come up tails is always the same: 50 percent. This is why after each toss, approximately half of the pennies are removed.
In this model, the removal of a penny signifies the decay of a radioactive nucleus. The time it takes for half of the remaining pennies to be removed is called the half-
life. Since each penny has a 50 percent chance of decaying (coming up tails), each time it’s tossed, the half-life of the pennies in this model is about one toss.
Once we know the rate of decay of a radioactive element in an object (like the meteorites in the last video), we can determine its age. If an object is made up of 50
percent decay product, then the object has been through one half-life.
Count the number of columns you made during this first round of the experiment. Now, gather all of your group’s pennies and conduct the experiment again from
the beginning. This time, plot the number of tail-side up pennies on the next page, and then answer the three questions.

3. Name: Group Name:
STUDENT MATERIALS
Page 2
MODELING MEASURING TIME USING RADIOACTIVITY
BIG HISTORY PROJECT / LESSON 1.4 ACTIVITY
Directions: Do the exercise as described in the Process section of the previous page. Record the results from the two rounds of penny-tossing, and then answer
the three questions, below. Be prepared to discuss your answers with the class!
1. How many columns, or half-lives, did your pennies have in the first round of your experiment? How about in the second round?
2. Did you ever have exactly half of your pennies come up tails?
3. What if we did this experiment again, like this: Each student in class has a penny and everyone tosses their pennies at the same time. Those students whose
pennies land tail-side up, have to sit down. About how many students do you think would sit down after one half-life?
After two half-lives?
How many half-lives do you think your “radioactive” class has?
1 - heads 2 - tails