Activity/Demo Title: Viewing the Subatomic World Through Cloud Chambers
Activity/Demo overview:
Unless you have superpowers, it is impossible to view subatomic particles such as protons and electrons with the naked eye. Or is it?
It turns out that specialized devices known as cloud chambers allow us to accomplish this seemingly impossible task. Invented in 1911 and used in the 1930s to discover both the positron and the muon, these particle detectors make the subatomic world visible through the phenomenon of condensation. The modern iterations are known as diffusion cloud chambers, and a typical setup involves releasing evaporated alcohol (isopropanol) into a chamber which cools as it passes through a steep temperature gradient. This creates a layer of supersaturated vapor. When an energetic charged particle, such as an electron or muon, passes through this vapor, nearby molecules can be ionized and act as condensation nuclei, yielding white tracks of condensed droplets that are large enough to be viewed with the naked eye.
Two of the most striking events which can be clearly seen in a cloud chamber are radioactive decay and cosmic muon detection. Here is a video showing radioactive decay emitting from an Am241 sample. This video shows a Uranium sample. This video shows a cloud chamber operating with different samples and provides insightful information on what is happening.
I am very new to the study of cloud chambers and can’t write too much about how we could go about putting one together. However, I really think it would be amazing to have one operating, for example, somewhere on the 2nd floor of Chamberlin (perhaps in the physics museum) that people could view. I think it could become one of our main attractions if we do it right! Though perhaps challenging, this sounds like a fun project and one that I would be happy to spend time leading and contributing to.
Activity/Demo Instructor Notes:
As a first step, the cloud chamber would need to be filled with the proper alcohol liquid to be evaporated, and then the heating, cooling, and lighting components would need to be turned on (the details of this step can be fully written out once the cloud chamber is built!). The instructor should be aware that the cloud chamber contains heating elements and be careful to avoid contact with them.
After this setup is complete and no radioactive samples are present in the chamber, visible tracks can be attributed to the natural radioactive background and cosmic ray muons passing through the supersaturated vapor. The process of charged particles inducing condensation in the vapor can be explained at this step.
The instructor can then put different radioactive samples into the cloud chamber and give a physics overview of the radioactive decay process occurring. They can also describe the different subatomic particles being emitted by the sample, such as alpha particles, which are leaving tracks.
Your experience in outreach
I was president of the University of Alabama’s Astronomical Society for 2 years during my time as an undergraduate student. In this role, I actively promoted physics and astronomy to students and community members through events such as public stargazing nights.
In graduate school, being a Wonders of Physics Outreach Fellow has allowed me to continue this exciting journey of sharing science with others. My main project was contributing to the Wonders of Physics Annual show alongside a fantastic group of other passionate individuals. I am greatly excited to become even more involved in outreach this upcoming year and inspire members of our community.