On the last day of recording the 2012 Christmas Lectures Dr Peter Wothers illustrates the properties of Air with a beautiful demo from his final Lecture.The Cloud Chamber shows the natural radiation in the atmosphere. When the charged alpha particles and smaller beta particles fire through the alcohol-heavy atmosphere in the chamber they cause little droplets to form leaving cloud-like trails.
When Dr Wothers introduces a sample of the artificially-produced radioactive metal Americium into the chamber the alpha particles emitted (with their two protons and two neutrons) grab electrons and form Helium atoms.
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