Detecting Cosmic Radiation Through a Cloud Chamber

By Jasmine Virk
Intermediate Category (Grades 9-10)
Innovation | Environment, Physics

We are bombarded with about 10,000 cosmic particles that enter every square meter of the Earth’s surface per second at approximately 1 GeV. We are unable to see, hear, or feel these cosmic rays. Approximately 100 million of these particles pass through our bodies every second without us knowing. However, through building a cloud chamber, I was able to see these particles.

Using a fish tank, rubbing alcohol, and dry ice, I designed a cloud chamber and used it to observe particles emitted from a source of radiation. At first, I used the cloud chamber without any radiation-emitting source and was unable to see any results. I determined that the best way to see radiation was to use a direct radioactive source. In my second attempt, I used part of a banana, which contains the radioactive isotope potassium-40. Even after using the banana, I did not see any visible signs of radiation. Consequently, I figured that I needed a larger source of radiation.

Cloud Chamber Setup

I considered that radon gas is naturally radioactive and is emitted from the soil beneath some houses. While radon gas is not the same as cosmic radiation, its common presence in homes gave me more reasons to try to detect radiation. Therefore, in my final attempt, I placed the cloud chamber in the basement (as it’s closest to the ground) and was successfully able to see trails left by particles zipping through the cloud chamber.

The warm rubbing alcohol that was at room temperature in the sponges placed at the top of the tank, evaporated into the air inside the tank. As it approached the bottom of the tank it cooled down close to the temperature of the dry ice. When at the top, the rubbing alcohol behaved as gas, however, as it reached the bottom, it behaved like a liquid. This disturbance in the air created a cloud. As the particles zipped through the cloud chamber, they ionized the gas molecules while the evaporated alcohol molecules clumped together to form tiny droplets. In the end, I was able to see different types of particles passing through the cloud chamber. The large tracks observed were from the radon atoms spinning out alpha particles. The thin and straight tracks were from muons. Lastly, the wavy tracks were from the electrons and positrons that bounced off the rest of the particles, resulting in their wavy shape.

Inside the Cloud Chamber

Through this experiment, I became more aware of the safety of my surroundings. For example, I was able to examine visible signs of radiation in my house. After observing the radon gas atoms zipping through the cloud chamber, I can infer that my house is exposed to radon gas. Although the cloud chamber did not provide details regarding the amount of radiation in my surroundings, it was an inexpensive alternative to a Geiger counter.
Overall, I thank my mentor for assisting me in safely carrying out this experiment and helping with gathering the supplies needed.

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