Answer to Question #1582 Submitted to "Ask the Experts"

Q

I work in a public health agency and we get calls periodically about sources of radiation in consumer products. I am not familar with some of the sources that are the subject of some inquiries and would like to obtain information. We are often asked about "glow in the dark" items, like clocks, watches, road signs, etc. I know that there are new crystal inorganics that provide long afterglows in "glow in the dark" items and these are not radioactive, but I also have heard of the presence (and read on your Web site) of phosphorescent products that contain tritium and promethium being added to road signs, clock dials, watches, etc. Is this process still practiced today or is this a "thing of the past"? If this is still practiced today how does one discern whether an item may contain radioactive material? Is there a health risk associated with say someone who repairs/handles "glow in the dark" items such as clocks, signs, etc.?

A

Glow-in-the-dark (GITD) materials have been around since the mysterious Bologna stones (BaSO₄) of the 16^th century and are quite commonplace today. GITD materials require energy, usually in the form of light, to become activated or "charged." Once activated, the after-glow lasts from seconds to hours, depending on the type and amount of trace activator present, the temperature, and the intensity of the ambient light. However, by employing radionuclides with long half-lives, the energy source can be self-contained and emit light for years. A variety of radionuclides were used in radioluminescent products. These included tritium (³H), ⁹⁰Sr, ¹⁴⁷Pm, and ²²⁶Ra. The older the item (pre 1970s), the more likely it was to use ²²⁶Ra. The newer items are more likely to contain tritium or ¹⁴⁷Pm. The applications were seemingly endless, including aisle markers, aircraft instruments, azimuth indicators, bedroom-slipper buttons, bell pushes, bubble levels, chamber pot covers, circuit breakers, clocks, combination locks, compasses, connectors, depth gauges, doll eyes, doorknobs, exit signs, fire extinguishers, fishing floats, fishing lures, house numbers, instrument dials, jewelry, keyhole locators, keys, knobs, light wands, map readers, maps, marker buttons, marking tape, peloruses, pointers, poison labels, pull chains, religious statuary, rotary telephone dials, screw heads for wall switches, sextants, speedometers, steering-wheel locks, street signs, switches, telegraph dials, telephone mouthpieces, theater seat numbers, thermometers, thermostats, timers, transits, watches, weapon sights, and one of my favorites, the Tom Mix rings_Magic-Light Tiger-Eye Ring_Magic-Light Tiger-Eye Ring. How can you tell if the item is radioactive? If the intensity of the glow remains constant over a long period (several hours) in the dark, the item probably employs a radioactive source. However, the phosphors (but not the radioactivity) degrade over time. As such, the absence of a glow does not necessarily indicate that the device is not radioactive. The use of a radiation detector, for example, a Geiger-Mueller (GM) detector, can confirm the presence of radioactivity, but the radiation emissions from some sources (for example, tritium) might be too weak to be detected. In general, war surplus/military items and old timepieces should always be suspect until they are checked, particularly if there is evidence of luminous paint having been used. Some of these military items contained several microcuries of ²²⁶Ra, making breakage or contamination a real concern. Fortunately, radium is easy to detect with a Geiger-Mueller detector. Most GITD items available today in the United States are not radioactive. Those GITD items produced since the 1970s that are radioactive, for example, certain aisle markers, compasses, exit signs, watches, and weapon sights, contain either tritium or ¹⁴⁷Pm and are often marked with a radiation symbol, the identity of the radionuclide, and sometimes the activity. The radiological risks with these items are slight but care should always be exercised to avoid breakage, contamination, or direct contact with the source material. As a generalization, only those items containing radium or strontium might present any radiological risk. If radioactive material is present or suspected, care must be exercised to avoid ingestion or spreading contamination. The simple handling of such devices would not normally be a problem. However, there have been cases where radioactive material was spread around when such items were cleaned (for example, the dials and hands of watches or clocks that contained radium). Contact your state radiation control office for advice concerning the proper method of disposal rather than discarding a radioactive item in the trash. In many instances, radioactive products can be returned to the manufacturer for disposal. William Kolb and Paul Frame, CHP, PhD A good Web site for information on radioactive watch dials is Wayne Schlitt's Elgin Watch page. For more information on radioluminescent products and activity levels, see the references identified in the answer to your follow-up question Q1583.