Tritium is very popular on gun sights as well- as it's a glow in the dark sight that doesn't need to be charged. I'm now questioning the practice of appendix carrying with tritium sights.
Tritium decays by beta-decay (an electron). The electron can not travel very far in air (1/4 inch), and is stopped by even the thinnest piece of metal. It's even stopped by the dead outer layer of your skin.
Not quite: beta decay will penetrate the skin enough to damage living tissue - beta burns are what caused the fatalities of the Chernobyl first responder fire fighters.
They spent a few hours covered in dust on their coats, and did a bunch of subsurface skin damage which manifested as third degree burns. Sepsis, not radiation poisoning, generally killed them.
Well, it lasts for several years, but considerably less than even a human lifetime: Tritium's half-life is only about 11 years, so gun sights, dark-proof glow-in-the-dark signage (usually reserved for critical industrial plants, ships and offshore platforms due to expense), etc, will become seriously degraded in just a few years. (Since the glow is directly proportional to the remaining low-level beta radioactivity, which can barely penetrate the glass envelope in the first place - you'd get more radiation (from radium) living in a brick house than carrying 24-7.)
FWIW, tritium and a phosphor granule encapsulated in glass microspheres have been developed for self-illuminating runway paint, but again, no one really uses it because tritium is stupid expensive, and again, it' loses half its brightness in only a decade.
On the other hand, I've been told that Trijicon will replace their tritium gun sights for the lifetime of the original owner. I plan to live long enough to cost them money...
