Watches that glow without batteries?

Question

I am doing a science assignment on radiation. One of the questions asks why watches used to glow in the dark without batteries, how they did it and who it was harmful to. Does anyone know any good websites that could explain this? Please note Im only in year 9, so i dont want any websites with heaps of technical terms that I wont understand, thanks for your help :)

Answer 1

This was traditionally done with a radium compound as the radiation source, and activated zinc sulfide as the phosphor (a substance that fluoresces when hit with radiation, in this case).  Old watches that no longer glow may still be radioactive: the zinc sulfide wears out long before the radium, with a half-life of 1602 years, decays.

Modern versions replace radium with the safer tritium - with a half life of only 12 years, it decays quickly and does not leave behind long-term hazards.  I think for a brief period after radium was phased out, promethium was used.

Radium exposure most seriously harmed the workers in the watch factories: they were told to l**k the brushes to keep them sharp, and often ingested radium salts.  Many died of cancer or acute radiation poisoning - see the link.

In addition, many of the old factories are still polluted now, and the radioactive waste has the potential to cause harm to those living nearby.  One of the largest such factories is now a superfund site.