Answer to Question #11947 Submitted to "Ask the Experts"

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

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


If a hyalite opal is set into a ring, is the amount of uranium measurable? Does it release appreciably more energy when fluorescing? Ultimately, is it safe to wear the ring next to the skin daily for the next 50 years?


The bottom line for your concerns is that it is very unlikely that your gemstone, when mounted on a ring, would have any consequences for the wearer, for many reasons as follows.

First of all, the amount of uranium would be very small as a trace impurity in the opal. It only takes a small amount to cause fluorescence under an ultraviolet light. In fact, without fluorescence the small quantity of uranium in opal would be very difficult to measure. Also, fluorescence from uranium has nothing to do with it being radioactive—it is a property of the uranium mineral. Uranium has been incorporated as a coloring agent in glass since its discovery as a new mineral in 1789. The use of uranium for coloring glassware was especially popular from about 1910 to 1940 for light yellow Vaseline glass and dark green Depression glass. These pieces of glassware are now collectors' items found in antique shops everywhere. Actually, uranium is still being used today for coloring glassware. The US Nuclear Regulatory Commission (NRC) allows use of uranium in glassware up to 10% by weight, although only a fraction of 1% is commonly used. If you go to ebay and search on "uranium glass," you will find many items colored with uranium that are still being made today. The amount of uranium in use for coloring glassware today is likely much greater than the amount in your hyalite opal.

Second, uranium is primarily a beta-particle emitter, and beta particles are easily blocked by a small amount of material. Therefore, the beta-particle radiation from a trace amount of uranium in hyalite opal is self-shielded within the crystal. Thus, relatively little of the beta radiation from uranium is released outside of the crystal. Also, the beta-particle energy has nothing to do with fluorescence. The beta energy from uranium is a consequence of its being a naturally occurring radioactive element. This beta energy will be released from uranium at a constant rate having nothing to do with fluorescence.

Third, beta-particle radiation will not penetrate very far in tissues. Thus, even a very large exposure to beta radiation would likely cause damage only to surface or skin tissues, such as skin reddening. This requires a very high radiation dose of 3–5 sieverts (Sv) in a short time. The exceedingly high exposures required to cause skin reddening would not be possible from the small amount of uranium in opal. Furthermore, our skin is not very sensitive to damage from radiation, and the NRC allows 10 times higher doses to the skin than to the whole body.

Fourth, depending on the setting design of your ring, if you have any metal between the opal and your finger, the metal will also serve as further shielding to block beta particles.

Thus, my overall conclusion is that if your opal is placed in a ring, it will be safe to wear for the next 50 years.

Ray Johnson, MS, PSE, PE, FHPS, DAAHP, CHP

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 10 April 2017. 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.