Hi, I recently bought a glow-in-the-dark key chain, similar to http://tinyurl.com/zqf5sxb (image link). It is made from solid plexiglass, with a hollow cylinder in the middle, containing tritium. The electrons from the beta decay presumably hit a fluorescent wall on the inside of the cylinder, making the thing glow. Really cool! My question is: should I worry about beta decay happening inside 3-6 mm of plexiglass?