Kids Research Express

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

. Detectors that enable researchers to observe the tracks that particles leave behind are called track detectors. Spark and bubble chambers are track detectors, as are the cloud chamber and nuclear emulsions. Nuclear emulsions resemble photographic emulsions but are thicker and not as sensitive to light. A charged particle passing through the emulsion ionizes silver grains along its track. These grains become black when the emulsion is developed and can be studied with a microscope. A. Cloud Chamber The fundamental principle of the cloud chamber was discovered by the British physicist C. T. R. Wilson in 1896, although an actual instrument was not constructed until 1911. The cloud chamber consists of a vessel several centimeters or more in diameter, with a glass window on one side and a movable piston on the other. The piston can be dropped rapidly to expand the volume of the chamber. The chamber is usually filled with dust-free air saturated with water vapor. Dropping the piston causes