A cloud chamber, also known as a Wilson chamber, is a particle detector used for visualizing the passage of ionizing radiation. Invented in 1911 by Charles Thomson Rees Wilson, a Scottish physicist, it was designed to study cloud formation and optical phenomena in moist air. The device earned Wilson the Nobel Prize in Physics in 1927. Large cloud chambers have been crucial in scientific research, with notable examples located in prominent physics laboratories worldwide, such as CERN in Switzerland and Fermilab in the USA.
How it works?
The principle of a cloud chamber involves creating a supersaturated environment of alcohol vapor. When a charged particle, such as an electron, muon, or alpha particle, passes through this vapor, it ionizes the gas molecules along its path. The ionized molecules act as condensation nuclei, around which the vapor condenses to form tiny droplets, thereby making the path of the particle visible as a streak of cloud.
DIY cloud chamber
Building a cloud chamber at home can be a simple DIY project. At ICTS, we have built multiple versions of the cloud chamber of which one of the best working configurations was built using an open rectangular acrylic box (L x W x H = 15 x 10 x 8 cm), a thin (~ 3mm thick) Aluminium plate to close and air-tight the open side of the acrylic tank, 5 kgs of dry ice, isopropanol (IPA, 99.9 %), felt or sponges, double-sided tapes, glue, black paper sheets, torch or mobile flashlight, and a heating bag. By placing the metal plate over the dry ice and sealing the container with molding dough or cellotapes on the plate, we created a cold environment. Soaking the felt with isopropanol and placing it inside the lid above the cooled plate before sealing it had allowed the vapor to supersaturate the air inside the acrylic box. After 10-15 mins, when the Al plate is cooled down, tiny droplets of IPA (alcohol mists) were visible to fall down on the plate.
Depiction of cloud chamber setup and observed particle tracks
We observed that a semi-dark room with proper illumination arrangement significantly improves particle track visibility. When charged particles enter the chamber, they condense the supersaturated IPA vapor and make the track visible. Follow the cartoon depiction of the setup below for more clarity.
Cartoon depiction of the cloud chamber setup
Visualization of Tracks and Particle Interaction
Watch a video of the working cloud chamber recorded at the ICTS lab
The tracks visible in a cloud chamber differ depending on the type of particle and its interaction with the vapor. For example, alpha particles create thick, short tracks due to their heavy charge and mass, while electrons create longer, thinner tracks. The visible trails help physicists identify the type of particles and study their behaviors and interactions, such as decay sequences and collisions.
Conclusions
The cloud chamber remains a fascinating and educational tool, bridging historical and modern physics. It provides a visual and intuitive way to understand complex physical processes and the fundamental particles of our universe. Constructing a cloud chamber offers hands-on experience with radiation and particle physics principles for educational purposes or amateur science enthusiasts.
Resources:
- https://www.hep.phy.cam.ac.uk/scatter/cloud.html
- https://www.classe.cornell.edu/Outreach/LessonPlans.html
- How to build a cloud chamber?
- ICTP SCIFabLab cloud chamber
- Close view of the ICTS cloud chamber
Acknowledgments: This experiment has been successful with the help of integrated PhD students at ICTS, Prof. Mahesh Bandi (OIST), & Prof. Abhishek Dhar (ICTS)
For queries, don’t hesitate to write to: ikbal.ahmed@icts.res.in