Friday is here, and the weekly "A Taste of Physics" corner is back — number 12.
This time: the cloud chamber, ionizing radiation, and the use of ions as condensation nuclei.
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The cloud chamber is also known as the Wilson chamber, named after the Scottish scientist who invented it at the beginning of the 20th century.
By using a cloud chamber, it is possible to observe the tracks of radioactive particles and study their properties.
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The chamber's operation is based on several principles:
Supersaturation — the chamber is cooled thoroughly, so the air contains an especially large quantity of vapor that has not yet condensed into droplets.
Ionization — every atom contains protons with a positive electric charge and electrons with a negative electric charge.
Removing an electron turns the atom into a positive ion, because a positively charged proton remains without an electron to balance it.
Condensation — when particles are added to a supersaturated vapor cloud, the vapor condenses onto these particles and forms droplets. This process occurs, for example, in cloud seeding.
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When a radioactive particle passes through the chamber, it ionizes the atoms it strikes along the way.
Ionized atoms act as condensation nuclei, attracting the surrounding water vapor molecules to themselves in order to form droplets.
(The reason for this is that water molecules are polar — they have a positive pole and a negative pole. The negative pole is attracted to the positive ion, much like a magnet.)
The particle's path is observed as a trail of droplets it leaves behind.
The structure of the particle can be inferred from the length, width, and direction of the trail.
In addition, by applying a magnetic field, it is possible to control the particle's trajectory and thereby learn about its electrical properties.
The cloud chamber was succeeded by the bubble chamber, which operates on the same principle but is considered more advanced. The bubble chamber was itself later replaced by more modern and sophisticated detectors.
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