Very Easy Cloud Chamber

Every second the Earth is bombarded with muons, hadrons, electrons and positrons. To detect these elementary particles, companies like CERN have built very large and complicated detectors. However, detecting particles does not have to be that difficult. Follow these simple steps and discover how to build your own particle detector at home!

• Large clear drinking glass
• Metal black box
• Dry ice (frozen carbondioxide)
• Iso-propylalcohol (min. 91%)
• Felt
• Styrofoam plates
• Stanley knife
• Vaseline
• Plasticine
• Duct tape
• Double sided tape
• Scissors
• Isolating basis

In this experiment, isolating the metal box is crucial so the dry ice inside has a harder time evaporating. The isolation is done by applying styrofoam on the outside of the container. To make sure that the styrofoam does not come off you can attach it with either hot glue or double sided tape. It is recommended to use a black surface.

This step is only needed when you have a high metal box. It is important that the dry ice in the container makes contact with the surface on which the large glass will be displayed. You do not want to waste any dry ice, so instead decrease the volume of the container by placing several plates of styrofoam inside. Covering the edges with duct tape helps preventing the styrofoam to fray. The styrofoam also again works as an insulator.

To saturate the chamber (large glass) with alcohol, cut a piece of felt into the right shape and place it onto the bottom. When you flip the glass upside down, the felt-covered bottom has to be on the top. Here the felt is cut into circles so it can easily be slided in. If you have thin felt, use a double layer so the alcohol will be well absorbed.

You can stick the felt using hot glue or plasticine. When using hot glue, make sure only to add a few dots of glue to the edge of the felt, or it will take a lot of effort to peel the felt off. Plasticine makes applying and removing the felt easier so the chamber can be reused. The easiest way to apply the plasticine is rolling it into a large rod and place it into the glass.

To further optimize the isolation you can place the box on top of a thick syrofoam plate.

Now it is time to add dry ice. Make sure the dry ice will make contact with the top plate when you turn the container over by using the styrofoam filling you created in step 2.

Once the container is filled with dry ice, you can saturate the felt with isopropyl alcohol (91% or more). The cloud chamber will run longer if you add more alcohol, so don't be sparing! Keep adding alcohol until a small puddle appears, but prevent the alcohol from dripping onto the black plate since plasticine will hardly stick on a slippery surface. If necessary, clean the glass with any excess alcohol so your view won't be blurred.

Alcohol is not allowed to escape the glass, so the chamber has to be fully closed. You can use a combination of vaseline and plasticine which are both easy in use and can be added in desirable quantity. The most effective method is to first put some vaseline on the top side of the glass, then add plasticine to attach the glass to the black surface. If you are not sure about the isolation yet, you can add an additional layer of vaseline over the plasticine.

Ready for some action! Turn down the lights and use a white flashlight to lighten the cloud chamber. After ten minutes you will be able to see ghostly white tracks in the alcohol vapor, which represent the elementary particles that are shooting through the air.

Here are some of the results of the cloud chamber. The particles crossing the chamber have created cloud-like droplets which are visible to the naked eye. All three pictures show the long, straight track of a muon. Other particles you can detect are hadrons (short, fat tracks) and electrons or positrons (zigzags). If you see forked tracks, you witness particle decay! For more result, you can place a radioactive source into the chamber.