Cloud Chamber
Cloud Chamber, instrument used to track the paths of charged subatomic particles released by radioactive substances. Physicists learn about a particle’s charge, mass, and energy by observing its path as it moves through a cloud chamber.
A cloud chamber is an airtight container, varying in size from a few square centimeters or inches to a room large enough for a person to enter. The container has at least one glass window through which the particle tracks can be observed and photographed. In order to trace the paths of particles, which are invisible to the naked eye, cloud chambers cool a gas saturated with water vapor, methyl alcohol vapor, or ethyl alcohol vapor so the gas becomes supersaturated—so full of vapor that liquid would begin to condense out of the gas under normal conditions. The vapor in the gas will not condense, however, unless there are foreign particles in the gas that the vapor can condense around.
As a charged particle passes through the supersaturated gas in the cloud chamber, the particle interacts with atoms and molecules of the gas and vapor. This interaction turns the gas particles into ions, atoms or molecules with a positive or negative electric charge. The supersaturated vapor condenses around these ions in the gas, forming a visible string of liquid droplets that illuminate the pathway of the particle.
Scottish physicist and Nobel Prize winner Charles T. R. Wilson invented the cloud chamber in 1911. He had experimented with optical phenomena created by light shining through supersaturated water vapor since the 1890s. In 1896 he discovered that supersaturated vapor condensed around the ions created by X rays just as it did around any other foreign body.
The cloud chamber played a key role in the early discoveries about particle physics. It enabled physicists to study the behavior of individual atoms, to photograph the actual paths of ionizing particles, and to analyze the complicated interactions that take place between charged particles and individual atoms.
A cloud chamber is an airtight container, varying in size from a few square centimeters or inches to a room large enough for a person to enter. The container has at least one glass window through which the particle tracks can be observed and photographed. In order to trace the paths of particles, which are invisible to the naked eye, cloud chambers cool a gas saturated with water vapor, methyl alcohol vapor, or ethyl alcohol vapor so the gas becomes supersaturated—so full of vapor that liquid would begin to condense out of the gas under normal conditions. The vapor in the gas will not condense, however, unless there are foreign particles in the gas that the vapor can condense around.
As a charged particle passes through the supersaturated gas in the cloud chamber, the particle interacts with atoms and molecules of the gas and vapor. This interaction turns the gas particles into ions, atoms or molecules with a positive or negative electric charge. The supersaturated vapor condenses around these ions in the gas, forming a visible string of liquid droplets that illuminate the pathway of the particle.
Scottish physicist and Nobel Prize winner Charles T. R. Wilson invented the cloud chamber in 1911. He had experimented with optical phenomena created by light shining through supersaturated water vapor since the 1890s. In 1896 he discovered that supersaturated vapor condensed around the ions created by X rays just as it did around any other foreign body.
The cloud chamber played a key role in the early discoveries about particle physics. It enabled physicists to study the behavior of individual atoms, to photograph the actual paths of ionizing particles, and to analyze the complicated interactions that take place between charged particles and individual atoms.
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