Alpha particles can make sparks fly

This exhibit is currently not on display at Technorama.
Ionising radiation – in this case Alpha particles from a radioactive Americium source – makes the surrounding air conduct electricity. If the alpha particles reach the high-voltage grid, you can see see it sparking over. However, a piece of newspaper between the source and the grid is sufficient to stop the alpha particles, so that there are no longer any discharges.