Clouds produced in an expansion chamber by ultra-violet light

Abstract

Clouds are produced in an expansion chamber filled with air and water vapour by irradiating with ultra-violet light through a quartz window, and expanding shortly afterwards. It is shown that the condensation does not occur upon charged particles, but on certain electrically neutral nuclei, not yet identified. By varying the wave-length of the ultra-violet light it is shown that the condensation is initiated by atomic oxygen, liberated by the action of the radiation on oxygen molecules. Similar effects are produced when an intense beam of deuterons is passed into the chamber.