Bubble Chamber

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Bubble Chamber, device that detects and tracks the paths of high-energy subatomic particles released by radioactive substances. Subatomic particles are invisible to the unaided eye. Bubble chambers provide an indirect way for physicists to “see” a particle and learn about its charge, mass, and energy and how it interacts with other subatomic particles. See also Particle Detectors; Elementary Particles.

A bubble chamber contains liquid, often hydrogen or deuterium, heated beyond its boiling point. This liquid does not boil, however, because it is under pressure and all the impurities have been removed. As a charged particle moves through the liquid, it interacts with atoms and molecules in the liquid, making them ions, which are atoms or molecules with a positive or negative charge. The new ions that form along the path of the charged particles act as impurities, causing the liquid next to them to boil. The tiny bubbles formed by the boiling liquid behind the particle form a line that makes the path of the particle visible. This pathway is usually photographed for later analysis. American physicist Donald A. Glaser built the first bubble chamber in 1952.

The bubble chamber overcomes many of the disadvantages of the cloud chamber, a particle detector used before the bubble chamber’s invention. A cloud chamber uses a gas that condenses along the path of the subatomic particle. Because the atoms and molecules in a liquid are closer together than those in a gas, an incoming particle in a bubble chamber has more interactions than an incoming particle in a cloud chamber in the same amount of time. The greater number of interactions in a bubble chamber makes the paths of subatomic particles easier to photograph and track.

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