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We'll make a cloud chamber, and observe vapor trails. I don't know whether or not these are like the vapor trails we see in the sky when jet plans pass overhead.

Wrap a large piece of dry ice in a towel, and cut a circle in the towel to fit a quart jar lid. (The dry ice is used to cause an extreme temperature difference between the top and bottom of the container.) If you get confused, remember the top of the jar will become the bottom, because the jar will be inverted for this experiment.

Cut a circle of black velvet to cover the inside of the jar lid, and glue it in place. (The black velvet provides a good background for observing vapor trails.)

Cut a circle from blotter paper to cover the inside bottom of the jar. Hold it in place with glue or a bent piece of coat hanger wire.

Now rinse the outside of the jar with hot water to warm it. Saturate the blotter with rubbing alcohol, swish it around the sides, and pour off any excess. (Rubbing alcohol will form vapor better than most liquids.)

Screw the jar into the lid (which is embedded in the dry ice in the towel) leaving the jar inverted. Shine a bright light (at least 200 watts) from a projector or other source
directly into the jar.

You will see vapor trails forming when you look at the velvet in the container. This device is called a cloud chamber.

Radiation particles enter the jar and travel through the alcohol vapor. When particles collide with the vapor molecules, droplets form and cloud trails can be seen.

Scientists can recognize certain particles by the kinds of trails they produce. For example, nuclei (alpha particles) are heavy, and leave straight, dense trails; electrons (beta particles) are light, and leave irregular trails, because they are easily deflected by other particles.

To produce highly visible trails, place a radioactive watch (try it with a quartz-dial watch--your writer doesn't know if it will work the same or not, but radium-dial watches are not easy to find) in the lid of the jar or stick a radioactive pin in a cork and set the cork near one side of the lid. (Radioactive pins are not dangerous and can be obtained from most scientific supply houses.)

You might try photographing the trails using ASA 200-rated film and testing different lens openings and shutter speeds.

You might also research the work of Charles Wilson (1869-1959), the Scottish physicist who invented the cloud chamber

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