Engaging students: Half-life

In my capstone class for future secondary math teachers, I ask my students to come up with ideas for engaging their students with different topics in the secondary mathematics curriculum. In other words, the point of the assignment was not to devise a full-blown lesson plan on this topic. Instead, I asked my students to think about three different ways of getting their students interested in the topic in the first place.

I plan to share some of the best of these ideas on this blog (after asking my students’ permission, of course).

This student submission comes from my former student Kerryana Medlin. Her topic: working with the half-life of a radioactive element.

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How can this topic be used in you students’ future courses in mathematics or science?

Depending on when they take precalculus, this topic may appear earlier or later in chemistry. The following is the list of TEKS for this topic in chemistry.

112.35. Chemistry (12) Science concepts. The student understands the basic processes of nuclear chemistry. The student is expected to:
(A) describe the characteristics of alpha, beta, and gamma radiation;
(B) describe radioactive decay process in terms of balanced nuclear equations; and
(C) compare fission and fusion reactions.

This is likely the most immediate application the students will encounter, but this topic also appears in calculus and, later, in the topic of differential equations, since it involves exponential decay. This topic can also be brought up in environmental science to mention the lifetime of radioactive isotopes. When a student crunches the numbers on the lifetimes of these isotopes, they can see that sometimes a small action has a huge ripple effect, especially for isotopes that humans bring into the picture.

 

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What interesting things can you say about the people who contributed to the discovery and/ or the development of this topic?

Ernest Rutherford received a Nobel Prize in Chemistry in 1908 for his discovery of the half-life of radioactive materials and his insistence that we apply this information to find the Earth’s age (Mastin, 2009). This later became more of a reality when Willard Libby started to develop carbon dating in 1946 (Radiocarbon Dating). Since then, carbon dating has been used to find the age of historical artifacts and bones, allowing historians to find more accurate time frames of events.

Carbon is not the only radioactive isotope. There are others which come to mind more readily when the word “radioactive” is used. These are typically the elements used for nuclear reactors. These are elements which readily undergo nuclear fission, which is the splitting of atoms, which releases energy. Uranium and Plutonium are the most common of these isotopes. Uranium-235 is the most commonly used for reactors and bombs (Brain and Lamb, 2000). This is probably the more interesting part of half-lives of elements and can extend the learning to an environmental issue such as nuclear waste, which takes an extremely long time to decay and which the U.S. Government has, in the past, not handled so well. (But I am not going into that, lest I go on a rant).

The last piece of history worth mentioning is fairly recent (and can be seen in real life and in the game mentioned later in this paper) which is that half-lives are not so clear cut. There is definitely a lot of estimating involved in the accepted half-life values. There is an article about this if you are interested (http://iopscience.iop.org/article/10.1088/0026-1394/52/3/S51/pdf), but I will leave it at this: much like most mathematical models, there is error in the half-life model, and the model formed may be a best fit, but there are always outliers for data and while carbon dating and half-lives of Uranium can give great estimates of what we are working with, they are not perfect.

 

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How can technology be used to effectively engage students with this topic?

For this topic, there is an interactive simulation posted on PHET. It lends itself to a guided worksheet which would allow students to use the simulations to create the functions for each half-life.
So the following would be an example of said worksheet without spaces for actual answers:

Radioactive Half-Life of Carbon-14 and Uranium-238

Please access the following website: https://phet.colorado.edu/en/simulation/radioactive-dating-game

Once there, download and run the game.

At the top of the game window are four different tabs: Half Life, Decay Rates, Measurement, and Dating Game. We will be going through each one in that order.

Some information about radioactive isotopes: An isotope is an element which has the same number of protons in its nucleus, but a differing number of neutrons, thus making it radioactive. These elements have lives which are defined by the time it takes to no longer be radioactive.

Part I: Half Life

Select the Carbon-14 atom and start placing the atoms in the white area. (The “add 10” tool is helpful here.) Then observe as each goes to Nitrogen-14 (This means the element is no longer radioactive and the radioactive isotope has run its course.)

What do you observe about the lives of the isotopes?

What time-frame do these lives fall into?

Do the same for Uranium-238 and record the time-frame.

Part II: Decay Rates

This part works by adjusting the slider and allowing the isotopes to run the course of their lives.

What does the graph on the bottom tell us?

How does one read the half-life of an isotope from this graph?

At what percent do we find the first half-life?

What is the half-life of Carbon-14 from this graph? Half-life of Uranium-238?

Part III: Measurement

On this one, you activate two separate events and then take readings of the amount of Carbon-14 and Uranium-238 in the objects.

Which item contains the Carbon-14? The Uranium-238?

Use the pause feature as you are taking the readings to find precise values of the half-lives.

At what percentages should we be reading the half-lives?

Use this data to create a function to model the half-life of both isotopes.

Part IV: Dating Game

Use your functions to estimate the date of two of the items (One C-14 and one U-238) in the dating game. Write down the name of the item and the estimated age of the item.

 

References:

Brain, Marshall and Lamb, Robert. (2000). How Nuclear Power Works. How Stuff Works. Retrieved from
https://science.howstuffworks.com/nuclear-power1.htm
Mastin, Luke. (2009). Important Scientists: Ernest Rutherford (1871-1937). The Physics of the Universe.
Retrieved from http://www.physicsoftheuniverse.com/scientists_rutherford.html
n.a. (2016). Willard Libby and Radiocarbon Dating. The American Chemical Society. Retrieved from
https://www.acs.org/content/acs/en/education/whatischemistry/landmarks/radiocarbon-dating.html
n.a. (n.d). Radioactive Dating Game. PHET Interactive Simulations. Retrieved from
https://phet.colorado.edu/en/simulation/radioactive-dating-game

 

 

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