Cloud chamber

A cloud chamber, also known as a Wilson chamber, is a <a href="/facts/Particle_detector/rYj0qKtA">particle detector</a> used for visualizing the passage of <a href="/facts/Ionizing_radiation/vw0d9GaT">ionizing radiation</a>.
A cloud chamber consists of a sealed environment containing a <a href="/facts/Supersaturation/YaTN0D1L">supersaturated</a> <a href="/facts/Vapor/PLlojGug">vapor</a> of <a href="/facts/Water/0lkXnJPK">water</a> or <a href="/facts/Alcohol_(chemistry)/Y0SCTDkh">alcohol</a>. An energetic charged particle (for example, an <a href="/facts/Alpha_particle/dzNMs9WP">alpha</a> or <a href="/facts/Beta_particle/x8b3ttLn">beta particle</a>) interacts with the gaseous mixture by knocking <a href="/facts/Electron/L0KBo5cW">electrons</a> off gas molecules via <a href="/facts/Electrostatic/bxkuW6s4">electrostatic</a> forces during collisions, resulting in a trail of ionized gas particles. The resulting <a href="/facts/Ion/wrbwhF3z">ions</a> act as <a href="/facts/Cloud_condensation_nuclei/8u5mVsFR">condensation centers</a> around which a mist-like trail of small droplets form if the gas mixture is at the point of condensation. These droplets are visible as a "cloud" track that persists for several seconds while the droplets fall through the vapor. These tracks have characteristic shapes. For example, an alpha particle track is thick and straight, while a beta particle track is wispy and shows more evidence of deflections by collisions. 
Cloud chambers were invented in the early 1900s by the Scottish physicist <a href="/facts/Charles_Thomson_Rees_Wilson/DlvmMa6u">Charles Thomson Rees Wilson</a>. They played a prominent role in experimental particle physics from the 1920s to the 1950s, until the advent of the <a href="/facts/Bubble_chamber/awVVhk4G">bubble chamber</a>. In particular, the discoveries of the <a href="/facts/Positron/HgV4zBzA">positron</a> in 1932 (see Fig. 1) and the <a href="/facts/Muon/BP2fLVIR">muon</a> in 1936, both by <a href="/facts/Carl_David_Anderson/rIMqD9ax">Carl Anderson</a> (awarded a <a href="/facts/Nobel_Prize_in_Physics/o6w1nCbr">Nobel Prize in Physics</a> in 1936), used cloud chambers. The discovery of the <a href="/facts/Kaon/Yn2w4QlQ">kaon</a> by <a href="/facts/George_Rochester/oz8ntg4x">George Rochester</a> and <a href="/facts/Clifford_Charles_Butler/9fSP9QlG">Clifford Charles Butler</a> in 1947 was made using a cloud chamber as the detector. In each of these cases, <a href="/facts/Cosmic_rays/uxCVdTKd">cosmic rays</a> were the source of ionizing radiation. Yet they were also used with artificial sources of particles, for example in <a href="/facts/Radiography/ab1bvq3q">radiography</a> applications as part of the <a href="/facts/Manhattan_Project/gtg8yRK2">Manhattan Project</a>.

Cloud chamber open-in-new

Cloud chamber