Radioactivity in Radium Painted Aircraft Gauge (Turn Indicator)

A very old General Electric brand aircraft turn indicator. These used to glow bright green in the dark, however radium painted dials lose their radio-luminescence after a few years. The strong alpha radiation emissions from the radium destroy the phosphor crystals, which is what "converts" the radiation's energy into light. They will still glow bright green with the assistance of a UV lamp as shown here. And even though the phosphor crystals have long been depleted, the radium paint is still quite radioactive. Keep in mind, these readings are taken with the radium paint behind a good thickness piece of glass which shields all the alpha, and a decent portion of the beta radiation. With the Ludlum 44-9 pancake probe right up against the gauge face, it reads around 11,000 CPM.