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Comment by Stratoscope | Hacker News Reader

When I was five or so, I had a watch with a radium dial.

I read in a kid's science book that if you went to bed and waited until your eyes were adjusted to the dark, and then held the watch dial against your closed eyelid, you would be able to see the sparks as individual radium atoms decayed.

I did this, and it worked! I could see each spark!

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Radium is primarily an alpha emitter. Alpha won't cross through the glass of the watch face, or even your skin. Maybe you were seeing the much more rare beta decays.

I doubt it was from the betas, they are all fairly low energy for typical radium. It was probably from the gammas produced by Ra-226. Ra-226 produces a 186 keV gamma in 3.3% of decays. Cherenkov radiation flashes in the eye are observed by patients undergoing clinical radiation therapy (see this interesting paper where this was explored and tested: https://www.redjournal.org/article/S0360-3016(19)33947-1/ful... ). The test done in the paper was with much higher energy gammas, but it is feasible that the 186 keV lines could cause the same effect.

I've never observed this when working with radium, but then I don't stick it in my eye.

I remember reading some witness accounts who saw nuclear explosions and they described being able to see through their eyelids (when closed) and in some cases even through their hands. Pretty wild when you think about how bright and forceful a nuclear explosion is.

Ball watches use Tritium in glass tubes for some really incredible lume https://shop.ballwatch.ch/en/

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