A Theory of Diffusion Cloud Chambers

Abstract

An attempt is made to understand quantitatively the effects of a given gas, gas pressure, vapor, ionization density, and temperature distribution on the operation of diffusion chambers. An integral equation is set up which takes into account diffusion of the vapor through the gas, removal of vapor by condensation, drop growth, and the motion of the drops due to gravity. Temperature distributions necessary to produce tracks through a given depth of a chamber are calculated, applying to a wide variety of different conditions. For example, the average temperature gradient for operation with methanol and air at 1 atmos or hydrogen at 10 atmos exposed to sea level cosmic radiation amounts to 3.6°C/cm while for air at 3 atmos or hydrogen at 30 atmos a gradient of 6.3°C/cm would be required. Because of the formation of uncharged drops at higher operating temperatures and because of the onset of semi‐stable convection currents in the light gases operation is expected to become difficult with air at a pressure >3 atmos or hydrogen at a pressure >30 atmos, or with ionization densities >4 times sea level cosmic radiation at 1 atmos of air.