Radium

due to its radioactivity dials using radium paint glow in the dark.

Radium is the 88th chemical element on the periodic table. All of its isotopes are radioactive. <upper>226</upper>Ra has the longest half-life -- 1600 years.

Radium was first discovered in 1898 by Marie Curie and her husband Pierre Curie. The pair shared the Nobel Prize in Physics in 1903.

Early researchers were not aware of the precautions necessary to prevent exposure to Radium causing cancer.

Radium's radioactivity was exploited to make paint that could be seen in the dark, where fluorescent chemicals lit up when struck by the radiation emitted by the Radium. There is a factory, where a very large fraction of the workers, who painted clock dials, died of cancer of the jaw. The explanation was that they all licked the tips of their paint brushes to get a find point, and this meant they got minute by deadly amounts of Radium on their tongues and lips.