C.T.R Wilson was the first person reported seeing and photographing "cloud tracks" formed by ionising radiation. The following photos are from the historic paper published in 1911.
His cloud chamber has a diameter of about 7.5 mm, with a height of approximately 4 to 5 mm before expansion, and 6.2 mm after. The ion clearing field was only 8 volts, which give a field strength about 16 Vcm-1.
Visual observation of the tracks was through a Nernst lamp (an early form of incandescent lightbulb) while photography was done with a specialized flash tube using Leiden jar arc discharges in heated mercury vapour at atmospheric pressure.
Alpha tracks emanating from radium-tipped spinthariscope source.
Wilson noted in his paper that this photograph did no justice to the beauty of the actual cloud chamber tracks. "The cloud condensed on the ions, while varying infinitely in detail, was always of the same general character."
Tracks due to cloud chamber exposed to X-rays. It is interesting to note that scientists at the time was still figuring out the nature of X-rays.
REFERENCE
C. T. R. Wilson, "On a Method of Making Visible the Path of Ionising Particles Through a Gas", Proc. Roy. Soc. A, Vol. 85, 578, pp. 285
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