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Turns out there's tritium illumination - a tiny very strong plastic tube will be covered in phosphor and filled with tritium. Tritium will undergo beta decay and a flow of electrons will cause the phosphor to glow.

This gives enough light for illuminating hours marks on a wristwatch dial and the hands of the wristwatch for many years and is claimed to not pose health hazard.

Now how it is possible to have energetic enough radioactive decay and no health hazard at the same time?

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The answer is provided on the page you linked to, under "health concerns". – pafau k. Sep 17 '12 at 14:25
up vote 2 down vote accepted

Because you keep the Tritium on the other side of the glass tube!

Tritium is a beta emitter, it sends out electrons, these are absorbed by the glass. More usefully they are also absorbed by the phosphor coating the glass which causes it to emit light.

The decay doesn't have to be particularly energetic, only enough to cause the phosphor to emit light. Also radioactive risk is a combination of activity; how much the isotope emits and how much of the isotope you have, the chemical nature of the isotope; what it binds to in the body and how long it stays there, and the type/energy of the emission; how much damage a single particle can do.

Tritium is a kind of Hydrogen so will form water and so can get into your body relatively easily, it's a low energy beta emitter so the particles don't carry much energy to do any damage and being water it doesn't accumulate in your body for very long.

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