## Lesson Plan for Girl with Pencil, Drawing: You Just Can’t Hide Your Age

February 11, 2017 by anniet16

__Station #4__: You Just Can’t Hide Your Age

__Grade Band:__ 6-12

A technique used to tell the age of various ancient artifacts is half-life. Half-life is the amount of time it takes for ½ of a sample of radioactive material to break down into a stable material. It is a specific amount of time for every radioactive element. All materials contain trace amounts of some radioactive element. Therefore, by measuring the ratio of radioactive material to the stable material it breaks down into, one can calculate the age of a rock, an artifact, Stonehenge, etc.

__Aim__: Students will

- Build a vocabulary
- Learn about half-life by doing the activity with manipulatives
- Relate half-life to telling the age of objects.

__Materials__:

The set of cards described below.

__Protocols:__

- Make a set of 3×5 cards for each of your groups as follows:
- The cards appear in pairs with labels on the back. Use red for radioactive, green for stable.

First pair

Card #1 is totally red, there is no card #2

Second pair

Card #1 is only half red, card #2 is half green

Third pair

Card #1 is only one quarter red, card #2 is ¾ green

Fourth pair

Card #1 is 1/8 red, card #2 is 7/8 green

Fifth pair

Card #1 is 1/16 red, card # 2 is 15/16 green

Sixth pair

Card #1 is 1/32 red, card #2 is 31/32 green

- Have students observe the pairs of cards to see how the process works.
- Students should then prepare a graph of the progress of radioactive decay using time for the x axis and amount for the y axis.
- Ask students how long it will take to have nothing left of the original radioactive sample.
- There are many radioactive substances called isotopes used to tell the age of objects. Carbon-14 is the most famous. Have students research carbon-14 and describe how it is used and on what types of objects and materials. Describe its limitations.

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