[SteveB]

Hi.

Today I was browsing eBay for watches with radium and I remembered that my mom still has a clock that's still in use, which looks like it MIGHT have some radium. I don't know exactly how old it is but it is fairly old. I'd like to know if there's actually radium, tritium, or something else on there.

I have some pictures of this clock... Sorry for the bad picture taking and for the odd-looking clock.

http://img245.imageshack.us/img245/8246/radiumradon1ui2.jpg

http://img169.imageshack.us/img169/9011/radiumradon2wm7.jpg

http://img119.imageshack.us/img119/3766/radiumradon3cp6.jpg

I put the clock under UV light and the area with the light green absorbed the light and turned a bright green. It does not glow in the dark though. I'm not sure if it's radium or anything else that I could take into my collection.

If you know what it could be, please let me know.

Thank you,

- Steve

[pantone159]

I don't know any good way to tell if there is Ra other than a Geiger counter or such.  (In which case it is obvious.)  The hands not glowing in the dark doesn't mean much, as I think the phosphor degrades fairly rapidly (unlike the Ra which takes millenia to go away) and then the hands don't glow much after that.

[billnotgatez]

²²⁶Ra, has a half-life of 1602 years

This is a link to some information about radium
http://en.wikipedia.org/wiki/Radium

I would think it still would be self-illuminating.

[SteveB]

Any idea what it could possibly be if it's not radium? What purpose do those spots serve?

- Steve

[Mitch]

Probably is Radium.

[pantone159]

I would think it still would be self-illuminating.

You are correct that the radium is still there, but the phosphor isn't.  (Or it's broken, or something.)  So it might not glow (it would, if it got a fresh coat of phosphor paint, though).  It would still be fully radioactive.

[billnotgatez]

I stand corrected.

http://en.wikipedia.org/wiki/Radioluminescence

An example of a common radioluminescent material is the tritium-excited luminous paints used on watch dials and gun sights, another is the now-disused mixture of radium and copper-doped zinc sulfide paint used historically to paint clock dials.

[pantone159]

Promethium has been used as well.  I think tritium is supposed to be the safest, so that is what would be in a modern self-illuminating whatever.

[SteveB]

I'm interested. Any specific things it was used in?

- Steve

[pantone159]

Any specific things it was used in?

Watch hands again, I think.  Maybe some scuba diving equipment (gauges) has used the stuff.  AFAIK, it is no longer used, tritium is what is used nowadays.

[jdurg]

I really doubt that it's radium.  The clock does not appear to be old enough to have been made during the early radium craze where no markings were required.  In later years (Typically Post WWII), they were required to put some type of symbol down by the 6 on the watch/clock face.  (Not neccessarily denoting radium, but denoting that it contained a radioactive paint).

In the later part of the era in which self-illuminating paints were used, Promethium-147 was used because it was less problematic than the radium paints were and depending on where the manufacturer was located it was cheaper than radium paints as well.  (China and Japan made great use of Promethium based luminescence, and the indication of 'MADE IN CHINA' on your clockface makes me think that perhaps it is a Pm-147 based paint.  Again, however, you would expect to see some indication of the promethium paint by some sort of label).

If the clockface used Pm-147, you'll have nothing left at this point in time.  The half life of a couple of years means that based upon a stop date of 1976 for the use of radioactive paints (I know they stopped in the 70's, but I can't recall the last year), your Pm-147 would have gone through about 15 half-lives.  That means you have 1/2^15 of the original tiny amount of promethium left.

While the phosphors do die over time, they don't die completely.  If you take your clock and keep it in a dark place for a day, then look at the face in the dark, if it used a self-illuminating paint you should see the tiny faintest of glow from the painted areas.  It may not be much, but if you match it to a non-radioactive based paint you'll notice it.  If there is absolutely no glow, then there is no activity left.

Honestly, the best way to tell is to pick up a geiger counter, or an even cheaper method is to pick up some polaroid film.  Take one sheet of the polaroid film and put it right down on top of the watch face and leave it there for about 24-48 hours.  Then open up the film to develop it.  If the face is using radium, the intense gamma rays will expose the covered film in the area that the paint exists and that will show up on the polaroid.  This is the easiest, and cheapest if you don't have a geiger counter, to see if Ra paint was used.