12/31/2023 0 Comments Radium watches and clocks![]() The average annual dose from naturally occurring radiation in the United States is about 3,000 µSv y -1. The discussion in the link above shows that typical radiation doses from radium in watches could reach a few tens of microsieverts per year (µSv y -1). The alpha and beta radiation are blocked inside the watch. The gamma rays from the radon decay products lead-214 ( 214Pb) and bismuth-214 ( 214Bi) are the source of potential radiation exposure to someone wearing a radium wristwatch. The radium, after emitting an alpha particle, is transformed into radon, which further decays to form a series of additional short-lived radionuclides that emit alpha, beta, and fairly strong gamma rays. This is the basis of radium paint for illumination. (Radium also emits a very weak gamma ray.) The alpha particles from radium will interact with crystals of zinc sulfide (ZnS) to produce a greenish glow. This isotope is primarily an alpha-particle emitter with a half-life of 1,600 years. The isotope of radium used for illumination is radium-226 ( 226Ra). After the war, the radium industry expanded further for illumination of pocket watches, wristwatches, clocks, and for other uses of radium in medical applications. This eventually led to an industry for extracting radium from uranium ore and radium became widely used in World War I for illuminating instruments in military aircraft, so pilots could read their instruments at night. ![]() This was an astounding observation and showed the world that radium could be a useful source of energy. The vial glowed brightly in the dark without any outside support, such as electricity. Pierre made national news about 1903 when he invited dinner guests to the front steps of his house in Paris one night and proceeded to remove a vial of radium from the vest pocket of his jacket. The Curies observed that purified radium will glow blue. Of course it all goes back to the discovery of radium by Marie and Pierre Curie in 1898 and the isolation of a physical quantity of radium in the early 1900s. See the Oak Ridge Associated Universities website for a good discussion on such uses of radium. I would like to respond to your questions by providing some historical information on how radium came to be used for illumination. You may be interested in the response to a similar question, Question 8650. The bottom line for your concerns is that no special handling is required for radium-dial watches, except that you should not open them or attempt to remove the radium paint, which could result in radium ingestion. You have raised thoughtful questions no doubt arising from your engineering interest in how things work. Should these old watches be handled in a special way, or should one just avoid them altogether? Can watches that do not have radium luminous paint but are stored in the same location as radium-containing watches become radioactive themselves i.e., could the gamma rays ionize them? I just don't know the majority of people wouldn't give it a thought, but as an engineer I can't dismiss the possibility so easily. Since I don't see any evidence of such regulation, I might conclude that they must not be a source of gamma radiation any longer. If these watches are still active sources, that implies to me that they would be regulated by the Nuclear Regulatory Commission (NRC). My question is: What isotope of radium was typically used and what is its half-life? I see these watches in antique shops, jewelry stores, and online, and I wonder if the radium is still bombarding everything within line-of-sight with gamma radiation, or if it would have completely decayed by now, 70-plus years later. Back then, the luminous paint applied to the hands and indices on the dials contained radium, which was obviously found to be harmful to the wearer later on and in part prompted adoption of tritium compounds in luminous paint. I have a keen interest in vintage wristwatches, especially military ones from World War II.
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