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Cloud chamber demonstration

This is just too cool to pass up.

Despite it being common knowledge in the scientific community, many people don’t know that there is radioactive decay going on all around them – and it’s perfectly safe. Background radiation comes from many natural sources, including the radioactive potassium-40 in the bananas you eat.

Radioactivity has three common “flavors”, though there are a number of other decay processes. Alpha decay occurs when an atom expels a helium 2+ atom and decays to a lighter element, beta decay is the release of an electron, and gamma radiation is the release of a highly energetic photon. Alpha particles can be blocked by a piece of paper, while gamma radiation is only attenuated by a slab of lead. Luckily, background radiation tends to be mostly of the alpha variety.

In the video below, a cloud chamber is used to detect background radiation, as well as to illustrate the radioactivity of Americium and radon gas.

A cloud chamber is a sealed container which usually contains supersatured alcohol. Supersaturation means that the relative humidity of the vapor is greater than 100%. While this seems impossible, it’s in fact a common occurrence in clouds (you can get supersaturations in excess of a few percent in the vigorous updrafts of a thunderstorm). Water cannot spontaneously condense without the aid of a condensation nucleus – a particle like sodium chloride, for example – due to the energy requirements necessary to overcome surface tension, among other things. If you supersaturate a chamber of water and then inject condensation nuclei, a cloud will form instantly.

A cloud chamber operates on a similar principle. Without condensation nuclei in the isolated chamber, you can reach high supersaturations without producing condensation droplets. As an atom undergoes radioactive decay, the radiation ionizes the supersatured vapor. These ions act as condensation nuclei and essentially trace the path of the emitted particle through the chamber with little cloud streaks.

Very cool.

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