Physicist studying alpha radiation in a cloud chamber. The flower-like pattern in the centre of the chamber is formed of the tracks of alpha particles emitted by a polonium source at the centre. A cloud chamber allows the tracks to be seen as the ionising particles cause the condensation of a supersaturated vapour as they pass through it. This study was being done during research into the effects of radiation on the components of a proposed nuclear-powered aircraft. The work was carried out by the National Advisory Committee on Aeronautics (NACA). This photograph was taken on 12th September 1957. NACA was absorbed by the newly-created NASA in 1958, and the nuclear-powered aircraft research was cancelled in the 1960s.