This is one of my favorite chemistry topics since its also a topic in physics. I pulled out an old slide show on nuclear physics, different types of nuclear reactions, fission, fusion, atomic bombs, power plants, all the good stuff. We did the activities ‘Simulation of Nuclear Decay Using Pennies and Paper’, from the Modern Chemistry curriculum and built cloud chambers.
For the paper activity, I precut a bunch of paper strips from colored card stock and gave each student two strips. They placed the first strip on a graph to represent 100 percent of material. Half of that will decay in one half life so they take the second strip which is the same length as the first one and cut it in half. Tape the half strip next to the first one. Repeat with each remaining strip until you can no longer easily cut the strip. For this example we made the half life 1 minute, which is about the time it took to fold and cut the piece of paper to make the next bar.
The other part of this activity involved putting 100 pennies heads up in a box – this represents our ‘original’ sample of material. Students shook the covered box 5 times and then removed all the pennies that had ‘decayed’ (turned to tails). This should be roughly half the pennies. They then repeated the shaking and removing of ‘decayed’ pennies til they had 1 or 0 pennies left. Every shake was considered to be a half life of 10 minutes for the purposes of graphing their data.
Then we get to the fun part of class, making cloud chambers. A cloud chamber is a closed container with an isopropyl alcohol soaked felt pad inside it (near the top or sides) and black paper on the bottom. The alcohol forms a mist inside the container becoming super saturated near the cold bottom of the container which is sitting on dry ice. As particles zip through the mist it produces ions and the alcohol drops condense on these ions, leaving a visible trail. There are a lot of videos on the web explaining how to make cloud chambers. Here are the two I like, one by Jefferson Labs uses a petri dish to make a small cloud chamber and the one on ScienceFriday has instructions for using something bigger. The petri dish one works really well but its gets fogged up and you spend a lot of time wiping it off. I bought the dry ice and 91% isopropyl alcohol at my local grocery store. Our best cloud chamber was built from a cheap (thin and flimsy) plastic cookie (Dunkers) container from Trader Joe’s.
In the photo above you can see our radioactive rock and 4 trails from particles that were emitted from the rock. You can also see the alcohol mist/rain in the container. You don’t need a radioactive sample to put in the container, you will see trails from muons and other particles that are zipping by us all the time. Here’s two videos from class:
I asked students to watch these videos before class: