Name: ______Pd.: ______Date: ______

Objective:
1. Define the term, half-life.
2. Distinguish between parent and daughter elements.
3. Use this model to demonstrate half-life to others.
Materials needed:

clock or watch with second hand, sheet of paper, scissors.
Procedure:
1. Record the time.
2. Wait one minute, then cut the paper in half. Select one piece, and set the other piece aside.
3. Wait one minute, then cut the selected piece in half. Select one piece, then set the other piece aside.
4. Repeat step 3 until 9 one-minute intervals have elapsed.
Questions to consider:

Question / Answer
1 / In terms of radioactive decay, what does the whole piece of paper used in this investigation represent?
2 / What do the pieces of paper that you set aside in each step represent?
3 / What is the half-life of your element?
4 / What fraction of your paper was left after the first three intervals? Six intervals?
5 / What two factors in your model must remain constant for your model to be accurate?


Closure:

Discuss how does this model represent radioactive decay?


Teacher Notes:

Provide the following for each student:

one sheet of color paper or construction paper, one half sheet of plain white paper, scissors and glue

You need: one of everything the students have (for modeling the activity along with them) and a timer.

Things to explain before beginning:

•  The white paper represents the parent material before any decay. I usually let them make up a name for their element…like lilwayneium or something that is relevant (but clean) to them

•  The half life of our fake radioactive element is 1 minute…so every minute we will cut our paper in half,

•  The decay material will be set aside into a pile after it has been cut, not to be picked up again until the end of the activity.

•  The cuts need to be made so that each one yields two pieces that are as close to square as possible. The tendency is for some creative types to only cut in one direction, giving them a nearly impossible sliver to cut later.

•  They are not allowed to cut until the 1 minute timer goes off. Some just can’t help themselves so I have started making them put the scissors on the table and hold up the piece of paper they are going to cut.

•  While we are waiting, we discuss how much is in our parent piece (in our hands) and how much is in the daughter pile. We talk about percentages and fractions. We talk about how many half lives have transpired.

•  We do 9 half lives. Yes, that’s a lot. But they end up with this tiny little piece of paper that’s about ½cm by ¼cm. It’s doable and it really makes a point. When it starts getting really small, they need to be careful about accidentally blowing away their decay materials…particularly the tiny pieces.

After 9 half lives have transpired, I have them compare the amount of parent material to the amount of decay material. Then I have them glue that tiny little piece into a corner and label it as the remaining parent material.

Then I have them start gluing down their decay material. Some will stack them ‘wedding cake’ style or like blocks, others will stack them one on top of the other. If they do the latter, I make them take a marker and color the edges so they can be seen.

I have them label the decay material. Then they answer the questions and glue that to the back of their model and turn it in for grading. You can also do a quick check on the answers and have them keep the model as a study item.

Questions to consider:

Question / Answer
1 / In terms of radioactive decay, what does the whole piece of paper used in this investigation represent? / the parent (radioactive) material
2 / What do the pieces of paper that you set aside in each step represent? / the daughter (decay) material
3 / What is the half-life of your element? / 1 minute
4 / What fraction of your paper was left after the first three intervals? Six intervals? / after 3: 1/8
after 6: 1/64
5 / What two factors in your model must remain constant for your model to be accurate? / time (or rate of decay)
amount of decay (1/2 of parent material remaining)


Closure:

Discuss how does this model represent radioactive decay?

Answers will vary but basically they should correlate cutting the ‘parent’ paper in half each minute to a radioactive element decaying by half for each half life.