Answer to Question #12289 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
I am an avid watch enthusiast and often restore older wrist watches. This process usually requires completely disassembling the watch. My current project involves a watch that was manufactured in 1992 and likely used promethium-147 (147Pm) to create luminous hour indicators and hands. Will handling the dial and hands pose a health threat to me? Can I potentially contaminate my house, thereby putting my family at risk?
First, it is highly unlikely you are putting your family at risk. Although it is difficult to give you an answer that is absolutely correct without actual measurements of the amount of radioactive material that may be on the watch, it's not even certain that the watch is radioactive. The material on the watch dial and hands may not be 147Pm; rather, it may be a fluorescent or phosphorescent chemical.
But if it is 147Pm, the beta particles will not pose a hazard unless ingested in large quantities. This is a highly unlikely scenario—even if some of it rubbed onto your hands, and you touched your mouth.
Furthermore, if it is 147Pm, it has decayed away to a negligible amount. This is an old watch, and watchmakers quit using radioactive materials many years ago, replacing radioactive displays with fluorescent or phosphorescent chemicals or electronic displays. Prometheum-147 has a half-life of 2.6 years, and after 10 half-lives (26 years) the amount of radioactivity will be reduced to 1/14,000th of its original activity. That's clearly a small and even negligible amount of radioactivity.
So, in conclusion, handling the dial with your hands should not pose a health threat to you or potentially contaminate your house. Your family would not be at risk.
Orhan Suleiman, MS, PhD, FAPM, FHPS