Hi, Not quite, The raduim is still very active. The glow stops because the ZnS breaks down. The light emissson relies on the crystaline structure of the ZnS plus a small amount of doping, typically silver. The alpha particles break down the crytaline structrure causing the glow to weaken. Most will still show a very faint glow if you let your eyes adapt in complete darkness for about 15 minutes. One reason why stopped hands can darken the srystal of a watch more than the numerals is distance. Inverse square law applies, thae hands are about half the distance so four tine the radiation. Alphs leaves are even lower as even a inch or two of air will stop them. Robert G8RPI.
________________________________ From: Bill Hawkins <b...@iaxs.net> To: 'Discussion of precise time and frequency measurement' <time-nuts@febo.com>; 'Tom Miller' <tmil...@skylinenet.net> Sent: Thursday, 11 July 2013, 0:11 Subject: Re: [time-nuts] How dangerous if a Rb lamp broken? Since this thread doesn't appear to have a half-life, perhaps this needs some explanation. The zinc sulfide fluoresces when an atom or more of radium decays. The fluorescence will still occur in the presence of ionizing radiation. The radium, OTOH, is nearly dead. Probability says that some number of atoms will leave their radioactive state and become inert (Lead? I haven't got time to look it up so I'll share my ignorance with you. Someone will correct me and the thread will never die.) The rate at which a mass of radium becomes inert is expressed as its half-life, which is the TIME that it takes for half of the remaining radium to become inert. The decay is exponential, as are so many natural things. You'll need a sensitive Geiger counter to see if there's any life left in the radium. Or you could expose the watch to a photomultiplier in total darkness to see if it scintillates. In other words, it doesn't burn out. Bill Hawkins -----Original Message----- From: Chuck Harris Sent: Wednesday, July 10, 2013 5:29 PM The dial is painted, the hands are actually metal frame, and the luminous paint is a wax that is put on the hand kind of like a soap bubble. The luminous material in the paint is very dead, as the hands and digits no longer glow at all. I guess there is a limit to how long ZnS:Cu can take the exposure and still glow. -Chuck Harris _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.