Alpha particle path

This animation shows the effect of an alpha particle passing through air saturated with a volatile liquid such as methylated spirits. As the alpha particle moves it produces ions along its path. These ions are invisible (but are shown in the animation as fine blue circles), as is the alpha particle itself (shown in the animation as a small yellow ball). Vapor condenses on these ions and it is these droplets of liquid (shown as pale blue bubbles) that are visible and show the path of the alpha particle.