[time-nuts] How dangerous if a Rb lamp broken?

[Bill Hawkins]

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