Answer to Question #8650 Submitted to "Ask the Experts"

Category: Consumer Electronic Products — Watches, Clocks, and other Glow-in-the-Dark

The following question was answered by an expert in the appropriate field:


I was a little alarmed by the information about older watches in the Health Physics Society fact sheet on radioactive materials in consumer products. I have a pendant that is the inside of an old watch. You see a small (about 2 cm diameter) silver disk with two cogs that you can move. It was explained to me when I bought it that the inside of old watches was meant to represent the heavens—the  larger golden cog was the sun, the smaller silver one was the moon, and when you held it up to the light, you saw little pinpricks for stars and ruby ones for planets. I have had this piece of jewelry since about 1995. I have handled it many times, as have many others, including kids. I'm wondering if I have to be concerned about this piece and about anything else it may have touched.

If I understand the fact sheet correctly, the radioactive material is in what may reflect light—the face or the hands—which would mean that what my pendant is made of is unlikely to be dangerous. However, I just want to make sure.


Your pendant is not dangerous! Even if it has radium, the amount of radiation emitted from such watch pieces is small, but potentially could be hazardous if ingested. For a definitive answer you would have to have this tested by a health physicist or laboratory with the proper instrumentation for detecting and properly identifying what the material is.

Other types of radioactive materials represent a much smaller risk than the radium, but without more technical information, it is simply not possible to assess what your watch contains. However, based on your description, I believe your watch does not contain radioactive materials, but phosphorescent materials that glow after being exposed to light for a short period of time.

In any case, as long as the watch is intact, the material is not touched, and (especially) the material is not ingested, you are safe. Again, for more specific analysis you should contact experts in radiation measurement; appropriate contacts would be your local university, hospital radiation safety officer, or health department, where they should be able to assist you.

I am attaching several URLs from several organizations, some of which provide additional links, which may be helpful:

The U.S. Environmental Protection Agency has an excellent and informative site.

The U.S. Nuclear Regulatory Commission has a publication (NUREG-1717) that discusses such products.

An interesting site is the Oak Ridge Associated Universities website, which discusses jewelry in more detail.

And finally, I will refer you to our own Health Physics Society site, which has many similar questions related to watches. Simply search on "watches."

I hope this is useful information.

Orhan H. Suleiman, MS, PhD

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
Answer posted on 18 December 2009. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.