A cloud chamber is an effective device for detecting radioactive particles by visualizing their paths as trails of condensed vapor.

Also known as a Wilson cloud chamber, this simple apparatus is designed to detect and visualize the trajectories of ionizing radiation, including alpha and beta particles, as well as gamma rays. The operation of the cloud chamber is based on the principle of supersaturation. Inside the chamber, the air is saturated with alcohol vapor to such an extent that any disturbance, such as the passage of a charged particle, triggers the vapor to condense into tiny droplets, thereby forming a visible trail.

The cloud chamber is a sealed environment that contains a supersaturated vapor of either water or alcohol. At the bottom of the chamber, a piece of metal—commonly lead or uranium—emits radioactive particles. As these particles traverse the vapor, they ionize the surrounding gas molecules along their path. This ionization process generates a trail of charged particles that serve as condensation nuclei. Consequently, the supersaturated vapor condenses onto these nuclei, resulting in a visible trail that corresponds to the trajectory of the radioactive particle.

The characteristics of these trails vary based on the type and energy of the radiation involved. For instance, alpha particles, which are relatively heavy and carry a double positive charge, penetrate the vapor and produce thick, straight trails. In contrast, beta particles, which are lighter and possess a single negative or positive charge, create thinner, more erratic trails. Gamma rays, being electrically neutral, typically do not leave a trail; however, they can occasionally eject a secondary electron from a gas molecule, which then creates a detectable trail.

The cloud chamber serves as a powerful tool for investigating radioactive decay and cosmic radiation. It enables us to visualize the otherwise invisible paths of particles, providing insight into their behavior. By analyzing these trails, we can identify not only the presence of radiation but also its type and energy, thereby gaining valuable insights into the properties of radioactive substances and the fundamental particles that constitute matter.