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Radium watch hands & luminescence

The vintage radium watch hands contains copper doped zinc sulfide, with little radium salt, is radioactive. The material in the watch hands has now mostly degraded, but very faint radioluminescence can still just be seen in total darkness once the eyes have accustomed to the darkness, and is visible as scintillations when viewed through 20x loupe in the computer generated still image at the bottom. However, much brighter green phosphorescence is produced for a time when illuminated with LW UV rays, as in a real photo in the middle; this is what the watch hands use to look like in the early days.

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Uploaded on April 1, 2008