Diffusion Chamber

Diffusion Chamber 

a device in which the visible tracks of charged particles may be observed. As in the cloud chamber, the tracks in a diffusion chamber are generated by droplets of liquid in supersaturated vapor, and the ions generated along the trajectory of the charged particle are condensation centers. Supersaturation of the gas in the diffusion chamber is achieved by maintaining a continuous stream of vapor from the hotter surface near the top of the chamber toward the cold surface at its bottom. In contrast to the cloud chamber, supersaturation in a diffusion chamber exists continuously; therefore, it is continuously sensitive to the ionizing particles. A diffusion chamber was constructed for the first time by the American physicist A. Langsdorf in 1936.

The metal bottom of the chamber, which is filled with gas, is cooled with solid carbon dioxide to a temperature of −60° to −70° C. A large vertical temperature gradient is established in the chamber as a result of the thermal conductivity of the gas and the convective heat transfer between the gas and the walls of the chamber. The upper part of the chamber is filled with methanol vapor at a vapor pressure close to saturation (at a temperature of 10°-20° C). The alcohol vapor diffuses downward and condenses at the bottom of the chamber. Since the temperature of the gas in the region adjacent to the bottom of the chamber is considerably lower than the temperature near the top, a layer of supersaturated alcohol vapor is formed in the lower part, where the particle tracks are formed. The layer that is sensitive to ionized particles is as thick as 50-70 mm. Clear particle tracks are formed in the sensitive layer at temperature gradients of ~50–10 deg/cm.

Diffusion chambers operating under high pressure are filled with hydrogen up to a pressure of 3–4 meganewtons per square meter (MN/m²), or 30–40 atmospheres (atm), and with helium up to a pressure of 20 MN/m² (20 atm). They are used in studying the interaction of high-energy particles with hydrogen, deuterium, and helium nuclei. Placement of the diffusion chamber in a magnetic field (~10,000-20,000 oersteds), makes it possible to determine the particle momenta with great accuracy. Diffusion chambers have been used in the studies of pi-mesons generated during collisions of protons, neutrons, and other particles with hydrogen and helium nuclei. Pair formation of lambda-hyperons and K-mesons was observed during collisions of pi-mesons with protons and other particles.

REFERENCE

Liapidevskii, V. K. “Diffuzionnaia kamera.” Uspekhi fizicheskikh nauk, 1958, vol. 66, fasc. 1.