I have pretty fond memories of the various physics classes I have taken, learning about wave/particle duality, the Millikan oil drop experiment, the Michelson Morley ether experiment, and other landmark events in the world of physics.
This evening I got on Instructables to take a look at more of the entries in the dead computer contest but before I could do that I saw an Instructable on building your own cloud chamber to observe the paths of decaying radioactive particles.
What a neat project, and easily within reach of every high school physics teacher. If you recall, a cloud chamber creates a condition where the atmosphere inside the chamber is supersaturated with alcohol, caused by a temperature gradient in the chamber that goes to a very low temperature. The alcohol evaporates in a warmer part of the chamber, and becomes supersaturated as it drifts into the cooler part. If the supersaturated condition is disturbed then the alcohol will condense into visible droplets.
In a particle physics experiment, the disturbance is provided by a radioactive sample placed inside the chamber. As the radioactive particles pass through the vapor they cause it to condense into a visible trail of droplets.
In this Instructable you will see a simplified cloud chamber built from a plastic food container and a small sponge, with the cooling provided by two stacked Peltier junction devices. The Peltier devices are solid state heat pumps that develop a hot side and a cold side when a voltage is applied. Which side is hot and which is cold is determined by the polarity of the applied voltage. In this case two devices are stacked, hot side to cold side, to increase the overall temperature difference.
The container is placed on the cold side of the Peltier devices (which are in turn powered by a PC power supply), an alcohol soaked sponge is attached to the lid, and the radioactive sample is placed inside the container. When the bottom of the chamber cools sufficiently the trails of vapor produced by the radioactive sample are clearly visible. This Instructable includes a video of the chamber in action, with samples of Americium, Autunite, and other radioactive ores. Be sure to watch it, it’s fascinating to see the different trails produced by the different ores.
Improvements?
The chamber is the main thing here, and in the Instructable the author comments that a dry ice based chamber is colder and has a larger area of supersaturation. Insulating this chamber should help and could be as simple as wrapping 3 sides with newspaper, or spraying with expanding foam from your local hardware store. You could also flip the container upside down and glue it to a piece of aluminum or other sheet metal with silicone glue. The sheet metal would them form the bottom of the chamber and would have better heat transfer from the Peltier device. A hold would be cut into the top of the chamber (the bottom of the container) to allow access, and a lid would have to be fashioned to close the chamber when in use. There are lots of other possibilities as well, if you have any leave a comment here or at the Instructible.
Best Regards,
Steve Ravet
EDN Gadgeteer
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