Some things for the readers with fewer introductions to Standard model of Particle Physics:- In the standard model there are twelve elementary fermions, six quarks and six leptons. The six leptons are three neutrinos and three electron-like particles. The three electron-like leptons are the electron, the muon and the tau particle. All three have negative charge and their spin is half. Fermions are thus grouped in three generations, each generation consisting of a charged lepton and its associative neutrino.
The cloud chamber is a particle detector invented by British scientist C.T.R. Wilson in the early twentieth century. For inventing this particle detector, he received the Nobel Prize in Physics in 1927. A cloud chamber consists of a sealed environment containing a super-saturated vapour of water or alcohol. The vapour condenses on the ionizing particle (alpha or beta), thus leaving a trail. The tracks can be seen with the help of a tangential light source. The bottom of the chamber is cooled. This creates a temperature difference between the top and bottom of the chamber.
Now coming back to the topic of building the particle detector, We need a transparent plastic container for the body and a metal plate for the bottom surface of the cloud chamber. The metal plate should be black to provide a suitable backdrop for the tracks. However, if you can’t get hold of a black metal plate then just paint it black or wrap it with black tape. Keep some putty or tape at hand to attach the container and plate to each other.
Next, we need a piece of felt. The felt will be used to introduce the alcohol into the chamber. And then you need some dry ice to cool the chamber. The local ice cream vendor parlour can help you out with getting dry ice if you don’t know where to get it. And to keep the dry ice you need an insulating box made from wood or thermocol. Get some ethyl or isopropyl alcohol from your school’s chemistry lab. Find a torch with a strong beam to provide the lightning. And you now have all your raw materials ready.
How do we put together a working cloud chamber or rather a particle detector from all these things? Stick the felt to the bottom of the plastic box. Soak it with the alcohol using a draper. Remember that the alcohol should not touch your bare skin. Also it is poisonous so do not try to drink it.
Put the box upside down on the metal plate. The felt lined bottom is now on top. Seal the box to the plate using the tape. Make sure the arrangement is airtight; otherwise you won’t get proper tracks. Now take the dry ice and put it below the metal plate. This sets up the temperature gradient and you should be able to see a sort of ‘rain’ at the bottom of the chamber.
Remember to handle the dry ice wearing gloves otherwise you will get a burn from the extremely cold ice. Also, the room should be ventilated because when the dry ice melts carbon dioxide will be formed.
Once you have completed all these steps turn off the lights in the room. Point the flashlight at the chamber from the side and wait for the tracks to appear. And there you have it, your own particle detector.
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