Radium clocks? Problems? Or not?

[zut]

My wife bought a bunch of old broken alarm-type clocks to use in her collage/assemblage artwork. They were kind of grungy, so she took them apart and cleaned them off. Now, a lot of these had glow-in-the-dark paint on the faces and hands, and this old paint would flake off here and there. She cleaned up real well and washed her hands, but I’m wondering… old clocks + glow-in-the-dark + flaking paint = problems? So…

1. When did manufacturers stop selling clocks with radium paint?
2. How can we tell for sure if the paint is radium or not (put them in the dark for a while and see if they still glow?)?
3. If it is radium, how dangerous are the clocks themselves?
4. How dangerous was scrubbing the clocks?

[andy_fl]

There is no significant health risk (http://hps.org/publicinformation/ate/q1673.html). However, it is not advisable to clean it in the future, because radiation exposure is inversely proportional to the square of the distance between source and you.

You have a higher risk from Radon - http://www.radonloc.com/faq.html - which may be there in your house.

Many modern dials (since Mid 60’s) use promethium or tritium instead of radium which is much safer.

[astro]

Well as long as you’re not planning on having kids…

You were tight to wonder as “cleaning them real good” was probably the absolute worst thing she could have done short of ingesting the paint. If she used gloves while cleaning and did not use a grinder or wire brush at any point there’s probably no problem. If she was “hands on” and using an abrasive brush or tool somehow turned the paint into an airborne dust which she accidently inhaled or ingested, this most likely not a good thing in the long run, however, chances are exceedingly small in real world terms that she got a dose from doing this that would be problematic.
Not a good plan for the long run however…
Commonly available radioactive sources

Radium paint Ra 226
This luminous paint contains a radium salt and some scintillating (fluorescing) substance, which makes it “glow in the dark”. It was used until the 1950s on the hands and faces of clocks and watches, as well as in instruments and meters that had to be read in darkness. Its use was banned, mainly because of the danger for the workers handling it.

Radium and its decay products emit alpha-, beta- and gamma radiation. The activity of radium dials can be astonishingly high. Typical figures are 0.1 to 1µCi (1µCi = 1e-6 Curie = 37kBq)

Items with radium paint are frequently found on flea markets and in antiques shops. Two examples are shown in the pictures to the right.

Top: watch from the 1950s, radium paint marks on face and hands. Count rate at 5cm distance 400/min with front glass, 1000/min without.

Bottom: luminous badge from WW II, diameter ca. 6cm. Estimated activity in the radium paint 70kBq. Count rate at 5cm distance 20,000/min. (!)

Radio active paint

That having been said, the important threat is inhaling or ingesting the stuff. This is a real danger that should not be taken lightly. Radium lodged in the lungs or digestive tract means a serious increase in the chance for cancer, because it sits there for a long time bombarding the same set of cells. The best way to handle radium paint that isn’t flaking is LEAVE IT ALONE.

Radiation Science and Health

“Radium poisoning” was known in the 1920s. Radium seeks bone. It replaces calcium. It is an alpha-emitter. At high doses, the radiation damage can cause bone degeneration (necrosis) and potential long-term cancer (osteosarcomas).
Radium decays to radon, a noble gas, which migrates to the blood stream to be discharged to the lungs (which distributes decay products and dose). Roughly 30% is exhaled. Radon decay products collecting in sinuses have caused head carcinomas.

[whitetho]

Cecil also addressed this issue in the first Straight Dope book: Is my glow-in-the-dark key ring harming my vital organs?