This isotope of radium has a half-life of 1600 years. It isn't dead, or even noticeably less radioactive.
Most probably it has burned out the binder that holds the ZnS:Cu material together and on the digits and hands. -Chuck Harris Bill Hawkins wrote:
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
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