Understanding Half–Life : Simulating the process of a radioactive material decaying according to the concept of a half-life.

Lakshmi Karthikeyan, Secondary Technical Education Program (STEP),
Anoka-Hennepin ISD # 11, Anoka, MN.
Based on
Chemistry in the Community – ChemCom, W.H.Freeman and Company, New York. 4th Edition, 2002.


In this activity, students will learn the concept of half-life and how it relates to radioactive material. Students will determine, with a hands-on experiment, the half-life of a radioactive element, "Coinheadsium". Students will create and be able to recognize a graph representing the half-life of a radioactive element.

Learning Goals

From this activity, students will understand that half-life is the time it takes for half of the radioactive material to decay (through either alpha or beta decay) into another element. This activity models the exponential decay curve of radioactive samples through several half-lives. The "decaying: atoms are pennies and decay is represented when a coin flips from heads to tails. The students will understand that atomic decay is a statistical matter, we will never be sure which particular atom will survive and which will decay at any given time.

Context for Use

Resource Type
Activity: Classroom Activity

Grade Level:
High School (9-12)

Lesson Format:
This is a classroom activity

Time needed:
One class period

Cardboard box
Graph paper

Concept Knowledge:
Radioactive elements change spontaneously through the emission of nuclear radiation, atoms of the element change to produce an atom of a different element by emitting an alpha or beta particle and energy called radioactive decay.
The half-life of a radioactive element is the time it takes for half of a statistically large number of atoms in a sample to decay into something else.

Description and Teaching Materials

The students will form small groups of three or four members.
After I review the concept of half-life, the students will simulate radioactive decay using a twizzler. Assuming the half-life of the twizzler to be 15 seconds, the students will figure out the length of the twizzler at the end of one half-life and cut it to that length. The students will continue and stop at the end of four half-lives.

In the next activity, the students will investigate the relationship between the passage of time and how many radioactive nuclei decay. They will assume that each heads-up penny represents an atom of the radioactive element "Coinheadsium". Its decay produces a tails-up penny, the element "Cointailsium".

The student groups will be given 100 pennies and a box. Placing all pennies heads up will represent the starting sample of "Coinheadsium". Each shake of the closed box will represent one half-life. During this time a certain number of "Coinheadsium" nuclei will decay to produce "Cointailsium". (that is some pennies will flip over)

The students will be given an activity sheet with the procedure and a table to record their observations. They will make a graph of "atoms surviving" versus "half-lives". They will answer a few post activity questions.

Teaching Notes and Tips

This is the first time that I am going to try this activity. I want all the student groups following the same procedure. I believe that providing them with an activity sheet will be useful.


Students will be assessed on their understanding of half-life via post lab questions and graph. Also they will do a work sheet with problems based on half-life.


I.B.1 – Scientific Inquiry
II.A.1 – Structure of matter

References and Resources