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1)We have radium clocks, watches, wrist bands and many things which glow because of radium but we know that radium is radioactive so why isn't it harmfull for us when in bands, watches etc.

2)Does it have enough energy to excite an electron?

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    $\begingroup$ The basic issue here is one of scale. Don't just here "radiation" and think "bad", ask "How much?". xkcd.com/radiation is a kind of layman's guide to real-life doses and danger levels. $\endgroup$ – dmckee --- ex-moderator kitten Apr 21 '15 at 4:09
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Humans can tolerate a certain amount of radiation. The watch contributes less radiation to our bodies than the soil. Radium emits x-rays, so yes, they can excite an electron.

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  • $\begingroup$ certain amount means what... please explain exact quantity $\endgroup$ – natarajan physicist Apr 21 '15 at 6:04
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    $\begingroup$ Why would electrons only be exited by gamma rays? Radium watch dials glow because the radiation excites orbital electrons of the paint material to a higher energy level and photons are emitted when they fall back. $\endgroup$ – Emil Apr 21 '15 at 7:49
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    $\begingroup$ "I don't think radium emits them" - Ra-226 emits x-rays. $\endgroup$ – Fermi paradox Apr 21 '15 at 10:12
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    $\begingroup$ "..the only form of radiation that would excite an electron would be gamma rays.." - Incorrect. Here is an interesting article on ionizing radiation $\endgroup$ – Fermi paradox Apr 21 '15 at 10:14
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One has to make clear that the watches we are using now are no longer using radium , because of radiation danger awareness.

Radium dials are watch, clock and other instrument dials painted with radioluminescent paint containing radium-226. The 1900s (decade) were the peak of radium dial production, as radiation poisoning was then unknown; subsequently, radium dials have largely been replaced by phosphorescent- or occasionally tritium-based light sources.

The radiation it emits is dangerous in large doses, but on a table top dial ignorable, . A hand watch worn continuously, like the new water resistant ones would be another story.

More specifically, natural radium (which is mostly 226Ra) emits mostly alpha particles, but other steps in its decay chain (the uranium or radium series) emit alpha or beta particles, and almost all particle emissions are accompanied by gamma rays.

Alpha particles have short range and their energy is what raises the luminescence in the radium compounds

Historically, a mixture of radium and copper-doped zinc sulfide was used to paint instrument dials giving a greenish glow. Phosphors containing copper-doped zinc sulfide (ZnS:Cu) yield blue-green light; copper and manganese-doped zinc sulfide (ZnS:Cu,Mn), yielding yellow-orange light, are also used. Radium-based luminescent paint is no longer used due to the radiation hazard posed to those manufacturing the dials.

Because of awareness of radiation dangers,

Currently, tritium is virtually the only radioisotope permitted to be used commercially as a radioluminescent light source. It is used on wristwatch faces, gun sights, and emergency exit signs. The tritium gas is contained in a small glass tube, coated with a phosphor on the inside. Beta particles emitted by the tritium strike the phosphor molecules and cause them to fluoresce, emitting light, usually yellow-green.

And current dials of watches must be using tritium mainly.

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By far the most common isotope of Radium is 226Ra, which decays by emitting an alpha particle. Alpha particles have almost no penetrating ability, and in general externally- occurring alpha particles are absorbed by the outer layers of skin which are naturally sloughed off, so no permanent damage occurs.

If you swallow it, that's a whole other (very sad) story, as it concentrates in the bones and the alpha particles can do serious damage. See "Radium Girls" http://en.wikipedia.org/wiki/Radium_Girls for a starting point.

And, of course, a watch case and dial glass will absorb any alphas from watch dials.

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It all depends on the amount of radiation to which one is exposed due to the day-to-day things used. Radium releases alpha particles which have very low penetrating power. Hence we are not in danger of those radiations.

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